Generation of superoxide anion and SOD activity in haemocytes and muscle of American white shrimp (Litopenaeus vannamei) as a response to beta-glucan and sulphated polysaccharide

Supplemental effect of dietary nucleotides on hematological profile, hepatic biomarkers, antioxidant capacity, and digestive functions in Sterlet sturgeon, Acipenser ruthenus

This study investigated the effects of dietary nucleotides (NTs) on hematological indices, hepatic biomarkers, antioxidant capacity, digestive functions, and intestinal histomorphology of Sterlet sturgeon (Acipenser ruthenus). Over 10 weeks, five diets with varying levels of NTs (0 g/kg, 1.5 g/kg, 2.5 g/kg, 3.5 g/kg, and 5.0 g/kg) were fed to triplicate groups of the fish (initial weight: 95.33 ± 1.23 g) in a flow-through system. The results indicated that final weight and relative growth rate reached the highest values in fish fed with the 5.0 g/kg NTs supplemented diet (p < 0.05). The fish fed NTs-supplemented diets also had lower feed conversion ratios than those fed the basal diet (p < 0.05). While total leukocytes were increased by increasing the dietary NTs supplementation to the highest value in the fish fed with 3.5 g/kg NTs, no significant differences were obtained in RBC, Hb, MCHC, HCT, and eosinophil values among the experimental groups (p > 0.05). The highest WBC count was seen in the fish fed with 3.5 g/kg NTs compared to the control group (p < 0.05). The serum hepatic enzyme levels generally decreased with higher NTs supplementation, although alanine transaminase significantly increased at the 5.0 g/kg level (p < 0.05). The antioxidant capacity was improved in the fish fed with NTs at 0.25 and 0.35 g/kg (p < 0.05), while the serum malondialdehyde level was decreased up to 3.5 g/kg NTs but it was increased at 5.0 g/kg (p < 0.05). The protease and amylase activities peaked in the fish receiving 3.5 g/kg NTs (p < 0.05), with the highest lipase activity obtained in 2.5 g/kg NTs (p < 0.05). The intestinal histology revealed that the fish fed with NTs at 3.5 g/kg exhibited the greatest villus height and width, along with more goblet cells (p < 0.05). Based on the second-order polynomial regression analysis, the optimum dietary levels of NTs for positive effects on physiometabolic responses and intestine functions of the Sterlet sturgeon lies in the range of 2.2-3.6 g/kg.

Nutritional Innovation Using Green Seaweed (Ulva sp.) and Garlic Powder Extracts for White-Leg Shrimp (Litopenaeus vannamei) Challenged by Vibrio harveyi

This study aimed to determine the antimicrobial effects of ethanolic extracts of Ulva sp. and garlic (Allium sativum) powder ethanolic extracts against Vibrio harveyi in vitro. The stimulatory effects of Ulva sp. extract (UE) and garlic powder extract (GPE) on the growth performance and innate immune responses of white-leg shrimp, Litopenaeus vannamei, and their challenge against V. harveyi infection were also investigated. A commercial shrimp diet (36.1% protein) was enriched with 0.5, 1.0 and 2.0 g UE/kg diet and 2, 4 and 6 g GPE/kg diet, whereas the control group was free of any supplement. Health juveniles of L. vannamei (average weight 2-3 g) were distributed in 21 fiberglass reinforced plastic (FRP) tanks (500-L capacity) at a stocking density of 300 animals/tank to represent each treatment in triplicate. The animals were fed ad libitum on the experimental diets up to satiety four times daily for 60 days. The phytochemical analysis of ethanolic extracts of Ulva sp. and garlic powder evoked their richness of several bioactive compounds showing significant antibacterial activity against V. harveyi. The GPE exhibited a higher inhibition zone than that of the UE. The supplemented diets did not significantly affect weight gain %, final weight, feed conversion ratio, specific growth rate and survival rates of white shrimp compared to those fed on the control diet. Significant increases were observed in total haemocyte count, phagocytosis and phagocytic index of all treatments compared with the control group. There were significant increases in serum total protein, acid phosphatase activity, alkaline phosphatase, lysosomal enzyme activity, phenoloxidase activity and superoxide dismutase activity with offered diets with increasing the levels of ethanolic extracts of Ulva sp. and garlic powder up to 2.0 g UE/kg diet and 6 g GPE/kg diet, respectively. The ethanolic extraction of Ulva sp. and garlic powder-supplemented diet groups, particularly at treatments of 2.0 and 6 g GPE/kg diet, respectively, significantly reduced the shrimp mortality induced by V. harveyi infection when compared with the control group. The net results evoked that ethanolic extraction of Ulva sp. (2.0 g UE/kg) and garlic powder (6 g GPE/kg diet) enhanced the immune response and disease resistance of the white-leg shrimp, L. vannamei. It is also noted that the GPE is more efficient than the UE in vitro and in vivo investigations.

Innate immune response of snakehead fish to Indian strain of snakehead rhabdovirus (SHRV-In) infection and the infectivity potential of the virus to other freshwater fishes

A new virus known as snakehead rhabdovirus (SHRV-In) was discovered in South India in striped snakehead (Channa striata) that had hemorrhagic patches and cutaneous ulcerations. The virus is the most potentially harmful pathogen of snakehead because it could cause 100% mortality within 5 days. The goal of the current investigation was to evaluate the infectivity of rhabdovirus in freshwater fishes and to analyze the immune response in snakehead fish after challenge with SHRV-In. The infectivity study of SHRV-In against three freshwater fish such as tilapia, grass carp and loach showed that the virus could not induce mortality in any of them. Snakehead fish challenged with SHRV-In showed significant (p < 0.05) changes in haematological parameters such as red blood cell (RBC), haemoglobin (HGB), haematocrit (HCT), mean corpuscular haemoglobin concentration (MCHC), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), white blood cell (WBC), total platelet (PLT) counts, mean platelet volume (MPV) and immunological markers such as respiratory burst, superoxide dismutase, catalase activity and myeloperoxidase activity at 6, 12, 24 and 48 hpi. Real time PCR was executed to examine the expression profile of innate immune genes such as IRF-7, IL-8 and IL-12 in Snakehead fish at 6, 12, 24 and 48 h post SHRV-In infection. Immune gene expression of IRF-7, IL-8 and IL-12 were up-regulated in the spleen when compared to kidney at 6 and 12 hpi. However, the expression level of all the genes was down-regulated at 24 and 48 hpi. The down regulation of innate immune genes after 24 hpi in these tissues may be the result of increased multiplication of SHRV-In by interfering with the immune signaling pathway.

Influence of stocking density on the growth, immune and physiological responses, and cultivation environment of white-leg shrimp (Litopenaeus vannamei) in biofloc systems

Biofloc (BF) stands out as a promising system for sustainable shrimp farming. Optimizing various culture conditions, such as stocking density, carbohydrate source, and feeding management, is crucial for the widespread adoption of the BF system. This study compares the growth performance of white-leg shrimp (Litopenaeus vannamei) in culture ponds at low density (LD) with 50 organisms/m2 and high density (HD) with 200 organisms/m2. Post-larvae of white-leg shrimp were stocked for 16 weeks in both LD and HD groups. The LD group exhibited a superior survival rate, growth rate, and feed consumption compared to the HD group. The BF from the LD system recorded a significantly higher protein content (16.63 ± 0.21%) than the HD group (15.21 ± 0.34%). Heterotrophic bacterial counts in water did not significantly differ with stocking density. However, Vibrio count in water samples was higher in the HD group (3.59 ± 0.35 log CFU/mL) compared to the LD group (2.45 ± 0.43 log CFU/mL). The whole shrimp body analysis revealed significantly higher protein and lipid content in the LD group. In contrast, the total aerobic bacterial count in shrimp from the HD group was high, with the identification of Salmonella enterica ssp. arizonae. Additionally, Vibrio counts in shrimp samples were significantly higher in the HD group (4.63 ± 0.32 log CFU/g) compared to the LD group (3.57 ± 0.22 log CFU/g). The expression levels of immune-associated genes, including prophenoloxidase, transglutaminase, penaiedin 3, superoxide dismutase, lysozyme, serine proteinase, and the growth-related gene ras-related protein (rap-2a), were significantly enhanced in the LD group. Conversely, stress-related gene expression increased significantly in the HD group. Hepatopancreases amylase, lipase, and protease were higher in the LD group, while trypsin activity did not differ significantly. Antioxidant enzyme activity (catalase, glutathione, glutathione peroxidase, and superoxide dismutase) significantly increased in the LD group. The histological structure of hepatopancreas, musculature, and female gonads remained similar in both densities. However, negative effects were observed in the gills' histology of the HD group. These results suggest that increasing stocking density is associated with significantly negative biological, microbial, and physiological effects on white-leg shrimp under the BF system.

Effects of geniposide on innate immunity and antiviral activity of Scyllaparamamosain

In this study, we examined the impact of geniposide on the innate immunity of the mud crab Scylla paramamosain, specifically in relation to WSSV infection. Through the use of in vitro cell culture experiments, we assessed the effects of geniposide on various parameters of hemocyte activity in S. paramamosain. Our findings revealed that high doses of geniposide inhibited hemocyte growth, with an optimal dose of 100 mg/kg determined. Additionally, we observed that geniposide increased the total hemocyte counts in S. paramamosain following WSSV infection. Geniposide also enhanced the enzymatic activities in hemolymph following treatment. The enzymes affected by geniposide encompassed ACP (acid phosphatase), POD (phenol oxidase catalase), PO (phenoloxidase), SOD (superoxide dismutase), CAT (catalase), and LZM (lysozyme). Furthermore, the activities of ACP, POD, PO, and LZM were also observed to increase subsequent to infection with WSSV. Notably, geniposide was found to enhance the phagocytosis of V. alginolyticus within the hemocytes. Geniposide can reduce hemocyte apoptosis rates after treatment, as well as hemocytes infected with WSSV. Furthermore, geniposide treatment significantly up-regulated the expression level of Myosin, but expression levels of Astakine, C-type lectin (CTL), STAT, JAK, proPO, minichromosome maintenance protein (MCM7), caspase-3 and crustin were down-regulated in the hemocytes. Additionally, geniposide treatment inhibited WSSV replication in hemocytes of S. paramamosain, and enhanced the survival rates of mud crabs following WSSV infection. These experimental results provide evidence that geniposide can improve the immune response by regulating humoral immunity and cellular immunity, and enhance pathogen resistance in S. paramamosain.

Dietary administration of yeast (Saccharomyces cerevisiae) hydrolysate from sugar byproducts promotes the growth, survival, immunity, microbial community and disease resistance to VP (AHPND) in Pacific white shrimp (Litopenaeus vannamei)

This study investigated the effects of yeast hydrolysate (YH) from sugar byproducts on various parameters in Pacific white shrimp (Litopenaeus vannamei). The study found no significant differences in water quality parameters across all treatment tanks, ensuring that the observed effects were not due to environmental variations. There were no significant differences in growth parameters between the control group and groups receiving YH at different dosages. However, the group given YH at 10.0 g/kg feed exhibited a notably higher survival rate and higher expression of growth-related genes (IGF-2 and RAP-2A) in various shrimp tissues. YH was associated with enhanced immune responses, including lysozyme activity, NBT dye reduction, bactericidal activity, and phagocytic activity. Notably, the 10.0 g/kg feed group displayed the highest phagocytic index, indicating a dose-dependent immune response. Expression of immune-related genes (ALF, LYZ, ProPO, and SOD) was upregulated in various shrimp tissues. This upregulation was particularly significant in the gills, hepatopancreas, intestine, and hemocytes. While total Vibrio counts remained consistent, a reduction in green Vibrio colonies was observed in the intestine of shrimp treated with YH. YH, especially at 5.0 and 10.0 g/kg feed dosages, significantly increased survival rates and RPS values in response to AHPND infection. The findings of this study suggest that incorporating additives derived from yeast byproducts with possible prebiotic properties obtained from sugar byproducts can lead to positive results in terms of enhancing growth performance, immunity, histological improvements, and resistance to V. parahaemolyticus, the causative agent of acute hepatopancreatic necrosis disease (AHPND).

Effects of environmental pollutant benzop[α]yrene on the innate immunity of Scylla paramamosain and its mechanism

Benzo[α]pyrene (BaP), a polycyclic aromatic hydrocarbon, is present in the aquatic environment and may be harmful to aquatic animals. We exposed the mud crab Scylla paramamosain to BaP for 7 days, the of superoxide dismutase (SOD), catalase (CAT), phenoloxidase (PO), lysozyme (LZM), glutathione (GSH), glutathione-S-transferase (GST), and acid phosphatase (ACP) activities in the hemolymph of mud crab were reduced. Additionally, the reactive oxygen species content was increased in mud crabs after exposed to BaP. When BaP concentration was increased, the total hemocyte count (THC), the survival rate of hemocytes and their proliferation were decreased. Histopathology analysis revealed damaged hepatopancreas cells, which indicating that BaP exposure is cytotoxic to crab hemocytes. However, the degree of DNA damage did not worsen with increasing BaP concentration. The expression levels of p53, MCM7, Caspase-3, and Myosin were changed with increasing concentration of BaP, which indicated that BaP exposure may affect apoptosis and phagocytosis in mud crabs. As BaP concentration was increased, the apoptosis rate of hemocytes was increased and the phagocytosis was decreased. These results confirmed that BaP exposure inhibited the innate immune response of mud crabs. A possible explanation for this effect is that BaP reduces the antioxidant enzyme activity and increases the reactive oxygen species content in mud crabs, thereby oxidizing and damaging hemocytes, which stimulates phagocytosis and apoptosis and negatively affects the innate immunity of S. paramamosain.

The immunomodulatory and antioxidant effects of β-glucans in invertebrates

β-glucans (βGs) are carbohydrate polymers linked by β-1,3, 1,4 or 1,6 bonds, they have been used to protect against potential pathogens and prevent lethal diseases. The immune system possesses several receptors that identify a wide range of structures and trigger cellular and humoral mechanisms. However, the mechanisms by which βGs activate the immune system of invertebrate organisms have not been fully clarified. This review is focused on evaluating the effect of βGs on innate immune system in invertebrates. βGs stimulate different cellular and humoral mechanisms, such as phagocytosis, oxygen species production, extracellular trap formation, proPO system, and antimicrobial peptide synthesis, moreover, βGs increase survival rate and decrease pathogen load in several species.

Evaluation of Yeast Hydrolysate in a Low-Fishmeal Diet for Whiteleg Shrimp (Litopenaeus vannamei)

An eight-week feeding trial was performed to evaluate the effects of yeast hydrolysate (YH) supplementation in a low-fishmeal diet on the growth, immune responses, intestinal histology and disease resistance of whiteleg shrimp (Litopenaeus vannamei). Five experimental diets were produced by supplementing YH at 0 (CON), 0.5 (YH0.5), 1 (YH1), 2 (YH2) and 4 (YH4) % to a basal diet containing 10% fishmeal and compared with a positive control with 25% fishmeal (FM25). Shrimp with an initial average weight of 0.43 ± 0.005 g (mean ± SD) were stocked in 18 tanks and fed the experimental diets (38% protein and 8% lipid) four times a day. Results showed that shrimp fed the FM25 diet exhibited significantly higher final body weight, weight gain, specific growth rate and protein efficiency ratio than those fed CON, YH0.5, YH1 and YH2 diets (p < 0.05). However, there were no significant differences between shrimp fed the YH4 and FM25 diets (p > 0.05). In addition, there were no significant differences in whole-body proximate composition, hemolymph biochemical parameters and non-specific immune responses among treatments. Intestinal villi length and muscular layer thickness of shrimp fed the YH4 and FM25 diets were significantly higher than the other groups. At the end of the bacterial (Vibrio parahaemolyticus) challenge test, shrimp fed YH4 and FM25 diets showed a significantly higher survival rate than those of shrimp fed CON, YH0.5 and YH1 (p < 0.05). These results suggest that supplementing 4% YH in diet containing 10% fishmeal could beneficially influence growth, intestinal morphology and disease resistance of whiteleg shrimp.

Effects of dietary soluble β-1,3-glucan on the growth performance, antioxidant status, and immune response of the river prawn (Macrobrachium nipponense)

The effects of dietary β-1,3-glucan on the growth performance, body composition, hepatopancreas tissue structure, antioxidant activities, and immune response of the river prawn (Macrobrachium nipponense) were investigated. In total, 900 juvenile prawns were fed one of five diets with different contents of β-1,3-glucan (0%, 0.1%, 0.2%, and 1.0%) or 0.2% curdlan for 6 weeks. The growth rate, weight gain rate, specific growth rate, specific weight gain rate, condition factor, and hepatosomatic index of juvenile prawns fed 0.2% β-1,3-glucan were significantly higher than those fed 0% β-1,3-glucan and 0.2% curdlan (p < 0.05). The whole-body crude lipid content of prawns supplemented with curdlan and β-1,3-glucan was significantly higher than that of the control group (p < 0.05). The antioxidant and immune enzyme activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), catalase (CAT), lysozyme (LZM), phenoloxidase (PO), acid phosphatase (ACP), and alkaline phosphatase (AKP) in the hepatopancreas of juvenile prawns fed 0.2% β-1,3-glucan were significantly higher than those of the control and 0.2% curdlan groups (p < 0.05), and tended to increase and then decrease with increasing dietary β-1,3-glucan. The highest malondialdehyde (MDA) content was observed in juvenile prawns without β-1,3-glucan supplementation. The results of real-time quantitative PCR indicated that dietary β-1,3-glucan promoted expression of antioxidant and immune-related genes. Binomial fit analysis of weight gain rate and specific weight gain rate showed that the optimum β-1,3-glucan requirement of juvenile prawns was 0.550%-0.553%. We found that suitable dietary β-1,3-glucan improved juvenile prawns growth performance, antioxidant capacity, and non-specific immunity, which provide reference for shrimp healthy culture.

The enhancement effect of low-dose dietary lipopolysaccharide on the growth and immunity of Litopenaeus vannamei, and transcriptome analysis

In this study, the effects of dietary lipopolysaccharide (LPS) on Litopenaeus vannamei were investigated to determine whether LPS could play a role as a potential immunostimulant in shrimp. L. vannamei with an initial body weight of 0.30 ± 0.02 g were fed a diet containing LPS at doses of 0, 0.2, 1, 5, 25 or 125 mg kg^-1 for eight weeks (groups LPS0, LPS0.2, LPS1, LPS5, LPS25 and LPS125, respectively). After eight weeks of feeding, the growth performance, immunity and transcriptome response of L. vannamei were analysed. Only dietary LPS at 0.2 and 1 mg kg^-1 resulted in a significant increase in the growth of L. vannamei (P < 0.05). According to the weight gain rate (WGR) and specific growth rate (SGR), the optimum dietary LPS level was 2.462 and 2.455 mg kg^-1, respectively. When compared with the control group, the survival rate (SR) of L. vannamei in the LPS0.2 group was significantly increased after white spot syndrome virus (WSSV) infection and the SR of L. vannamei in the LPS1 group was significantly increased after Vibrio parahaemolyticus infection (both P < 0.05). Compared with the LPS0 group, immune enzyme activity in the serum of L. vannamei could be significantly increased and the content of maleic dialdehyde (MDA) significantly decreased by dietary LPS. Transcriptome analysis of the haemocytes of L. vannamei identified 399 up-regulated differentially expressed genes (DEGs) and 5000 down-regulated DEGs in the LPS0.2 compared to the control group. Most of the DEGs were significantly enriched in the following pathways: phosphatidylinositol signalling, Wnt signalling, Jak-STAT signalling and inositol phosphate metabolism. In conclusion, this study revealed that diets supplemented with low-dose LPS had positive effects on the growth and immunity of L. vannamei.

Impact of Dietary Administration of Seaweed Polysaccharide on Growth, Microbial Abundance, and Growth and Immune-Related Genes Expression of The Pacific Whiteleg Shrimp (Litopenaeus vannamei)

This work aims to determine the impact of dietary supplementation of polysaccharide, extracted from brown seaweeds Sargassum dentifolium on growth indices, feed utilization, biochemical compositions, microbial abundance, expressions of growth and immunity-related genes, and stress genes of the Pacific Whiteleg shrimp Litopenaeus vannamei. A total of 360 post-larvae of L. vannamei were randomly distributed into a 12-glass aquarium (40 L of each) at a stocking density of 30 shrimp with an initial weight of (0.0017 ± 0.001 g). During the 90-day experiment trial, all shrimp larvae were fed their respective diets at 10% of total body weight, three times a day. Three experimental diets were prepared with different seaweed polysaccharide (SWP) levels. The basal control diet had no polysaccharide level (SWP₀), while SWP₁, SWP₂, and SWP₃ contained polysaccharides at concentrations of 1, 2, and 3 g kg^-1 diet, respectively. Diets supplemented with polysaccharide levels showed significant improvements in weight gain and survival rate, compared to the control diet. Whole-body biochemical composition and the microbial abundance (the total count of heterotrophic bacteria and Vibrio spp.) of L. vannamei showed significant differences among polysaccharide-treated diets compared to the control. At the end of the feeding experiment, the dietary supplementation of polysaccharide levels enhanced the expression of growth-related genes (Insulin-like growth factors (IGF-I, IGF-II), immune-related genes (β -Glucan-binding protein (β-Bgp), Prophenoloxidase (ProPO), Lysozyme (Lys), and Crustin), and stress genes (Superoxide dismutase (SOD) and Glutathione peroxidase (GPx) in the muscle tissue of L. vannamei. However, the current study concluded that the inclusion rate of 2 g kg^-1 of polysaccharide as a dietary additive administration enhanced both weight gain and survival rate of L. vannamei, while the incorporation level of 3 g kg^-1 reduces the abundance of pathogenic microbes and enhances the growth-, immunity- and stress-related gene expressions of L. vannamei.

Effect of dietary supplementation with Moringa oleifera leaf extract and Lactobacillus acidophilus on growth performance, intestinal microbiota, immune response, and disease resistance in whiteleg shrimp (Penaeus vannamei)

This study investigated the effect of the moringa (Moringa oleifera) leaf extract and Lactobacillus acidophilus individually or combined on growth performance, enzyme activity, intestinal and hepatopancreatic histology, intestinal microbiota, immune response, and resistance against Vibrio alginolyticus and Vibrio parahaemolyticus in whiteleg shrimp (Penaeus vannamei). Six diets were formulated: three diets without L. acidophilus containining 0 (control, ME0), 2.5 (ME2.5), and 5.0 g/kg of moringa (ME5.0) and the same three diets containing L. acidophilus at 1 × 10⁷ CFU/g of diet (ME0+P, ME2.5 + P, and ME5.0 + P, respectively). Growth performance was measured after 60 days of the rearing period. On the final day, the shrimp were sampled to assess enzyme activity, intestinal and hepatopancreatic histology, and gut microbiota. Shrimp hemocytes were examined on Days 0, 1, 2, 4, 7, 14, 21, and 28 to measure the immune response in terms of the total hemocyte count, phenoloxidase activity, phagocytosis, and superoxide anion production. Furthermore, the shrimp were challenged with V. alginolyticus and V. parahaemolyticus. The results revealed that ME2.5 + P significantly increased (P < 0.05) final weight, weight gain, specific growth rate, enzyme activities, and villi height compared with ME2.5 and control. Wall thickness was increased in the shrimp fed diet supplemented with moringa and L. acidophilus compared with the control shrimp. Hepatopancreatic histology revealed that R cells were more abundant in the shrimp fed diet containing moringa and L. acidophilus compared with those fed diet containing moringa alone (P < 0.05) at the same concentration. High-throughput sequencing analysis indicated that the dietary supplementation with moringa and L. acidophilus affected the gut microbiota composition. All gene functions, members of KEGG level 2, related to metabolism were increased in diet supplemented with moringa with or without L. acidophilus compared with the control group. The immune assay revealed that the total hemocyte count, phenoloxidase activity, phagocytic rate, superoxide anion production, and immune-related gene expression (including those of prophenoloxidase II, alpha-2-macroglobulin, penaeidin2, antilipopolysaccharide factor, crustin, lysozyme, glutathione peroxidase, and superoxide dismutase) were higher in the experimental groups than in the control group on several observed days; however, the increases were observed more often in the ME2.5 + P group than in the other treatment groups. Furthermore, the ME2.5 + P group exhibited a significantly higher survival rate (P < 0.05) in the challenge test against V. alginolyticus and V. parahaemolyticus. In conclusion, supplementation with dietary moringa and L. acidophilus at ME2.5 + P improved growth performance, immune system, and resistance against Vibrio in the shrimp.

Microalgae-Based Biorefineries: Challenges and Future Trends to Produce Carbohydrate Enriched Biomass, High-Added Value Products and Bioactive Compounds

Simple Summary

Microalgae-based biorefineries allow the simultaneous production of microalgae biomass enriched in a particular macromolecule and high-added and low-value products if a proper selection of the microalgae species and the cultivation conditions are adequate for the purpose. This review discusses the challenges and future trends related to microalgae-based biorefineries stressing the multi-product approach and the use of raw wastewater or pretreated wastewater to improve the cost-benefit ratio of biomass and products. Emphasis is given to the production of biomass enriched in carbohydrates. Microalgae-bioactive compounds as potential therapeutical and health promoters are also discussed. Future and novel trends following the circular economy strategy are also discussed.

Abstract

Microalgae have demonstrated a large potential in biotechnology as a source of various macromolecules (proteins, carbohydrates, and lipids) and high-added value products (pigments, poly-unsaturated fatty acids, peptides, exo-polysaccharides, etc.). The production of biomass at a large scale becomes more economically feasible when it is part of a biorefinery designed within the circular economy concept. Thus, the aim of this critical review is to highlight and discuss challenges and future trends related to the multi-product microalgae-based biorefineries, including both phototrophic and mixotrophic cultures treating wastewater and the recovery of biomass as a source of valuable macromolecules and high-added and low-value products (biofertilizers and biostimulants). The therapeutic properties of some microalgae-bioactive compounds are also discussed. Novel trends such as the screening of species for antimicrobial compounds, the production of bioplastics using wastewater, the circular economy strategy, and the need for more Life Cycle Assessment studies (LCA) are suggested as some of the future research lines.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

Combined administration routes of marine yeasts enhanced immune-related genes and protection of white shrimp (Penaeus vannamei) against Vibrio parahaemolyticus

Antibiotic usage to control infectious diseases in shrimp aquaculture has led to serious problems on antimicrobial resistance. An alternative to mitigate this issue is the use of probiotics, which can be easily administered by feed and water. This study examines immunomodulatory and protective effects of the marine yeasts Debaryomyces hansenii CBS8339 (Dh) and Yarrowia lipolytica Yl-N6 (Yl) -alone and mixed-in white shrimp Penaeus vannamei post-larvae. Administration routes (fed and water alone or in combination), supplementation frequency and time elapsed after the last dietary supplement were tested on growth and gene expression of penaeidin, lectin, lysozyme, superoxide dismutase, catalase, and peroxidase, as well as survival upon Vibrio parahaemolyticus IPNGS16 challenge. Penaeidin and lectin genes were upregulated in post-larvae fed orally with Yl or combined Dh + Yl. Higher growth and survival for yeast supplementation treatments were observed compared to the control group, mainly when yeasts (Dh + Yl) and administration routes (feed and water) were combined. In conclusion, mixed yeast and combined administration routes improved growth and immunity against V. parahaemolyticus.

Effects of dietary black soldier fly (Hermetia illucens Linnaeus) on the disease resistance of juvenile grouper (Epinephelus coioides)

An experiment was performed to study the effects of dietary levels of black soldier fly larva meal (BSFLM) on the growth performance, immunity and disease resistance of juvenile grouper (Epinephelus coioides). Four isoproteic and isoenergetic diets were formulated with dietary BSFLM levels of 0 g/kg (T0), 25 g/kg (T2.5), 50 g/kg (T5) and 100 g/kg (T10). Each diet was randomly fed to triplicate groups, each containing 40 fish. The results of the 30-day study indicated that fish growth performance was not affected in the T2.5 and T5 groups compared with the T0 group. In the group with a dietary BSFLM level of 100 g/kg, the feed coefficient was significantly higher than that in the other three groups. The superoxide dismutase, catalase, glutathione peroxidase, lysozyme activity, and malondialdehyde content in the liver, and the interleukin-1 beta (IL-1β), gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α) and heat shock protein 70 (HSP70) expression in the gills, head kidney, liver and spleen remained consistent in all groups. In addition, no significant differences in the cumulative mortality or parasite abundance in groupers after Vibrio harveyi and Cryptocaryon irritans infection were observed. These results suggested that BSFLM supplemented diets did not inhibit disease resistance in groupers.

In vivo study of a novel protein kinase C that mediates immunocompetence and catecholamine biosynthesis in hemocytes of Litopenaeus vannamei by using its potential competitive inhibitor, bisindolylmaleimide I

This study applied bisindolylmaleimide I (BSM), a pharmacological competitive inhibitor of protein kinase C (PKC) enzymatic activity, at 1.25 pmol shrimp^-1 for 60 min to investigate the potential involvement of PKC in signal transduction pathways in the hemocytes of Litopenaeus vannamei. A novel PKC in L. vannamei (LvnPKC) was identified and characterized and was determined to be involved in mediating the neuroendocrine-immune regulatory network. The hemocytes of L. vannamei that receive BSM exhibit significantly decreased PKC activity and LvnPKC gene and protein expression levels. Furthermore, the total hemocyte count, hyaline cells, and semigranular cells increased significantly along with significant decreases in granular cells, and meanwhile, the significantly increased phenoloxidase activity, respiratory bursts, superoxide dismutase (SOD) activity, phagocytic activity, and neutrophil extracellular trap were observed; however, phagocytic activity decreased significantly. In a molecular model, the gene expressions of lipopolysaccharide- and β-1,3-glucan-binding protein, peroxinectin, cytosolic manganese SOD, mitochondrial manganese SOD, and copper/zinc SOD in the hemocytes of L. vannamei that had received BSM decreased significantly, but prophenoloxidase I increased significantly. In catecholamine biosynthesis, tyrosine, dopamine, and norepinephrine decreased significantly in the hemocytes of L. vannamei that had received BSM, and l-dihydroxyphenylalanine increased. Moreover, tyrosine hydroxylase (TH) activity increased significantly, whereas TH and dihydroxyphenylalanine decarboxylase gene expression decreased significantly. These findings suggest that BSM inhibits PKC activity in hemocytes in which LvnPKC gene and protein expression are also inhibited. Additionally, the hemocytes' immunocompetence, including their prophenoloxidase and antioxidant systems, phagocytic activity, and catecholamine biosynthesis, was disrupted, confirming the roles of LvnPKC in mediating the neuroendocrine-immune regulatory network in hemocytes.

Effect of dietary protein levels on the growth, enzyme activity, and immunological status of Culter mongolicus fingerlings

A 65-day growth trial was conducted to investigate the dietary protein requirements for Culter mongolicus fingerlings. Isolipidic and isoenergetic diets were formulated with five dietary protein levels (32%, 37%, 42%, 47%, and 52%). Each diet was assigned to triplicate groups of 70 C. mongolicus fingerlings (0.99±0.08 g). The results indicated that weight gain and specific growth rate (SGR) increased with increasing dietary protein levels up to 47%. The activities of intestinal trypsin and lipase were the lowest in the 32% protein and 52% protein groups, while amylase activity reduced markedly in the 47% protein group. These results suggest that different dietary protein levels may cause different transformations of nutrients. The activities of superoxide dismutase (SOD) and lysozyme were not affected by varying dietary protein levels, except for those in the 32% protein group. In contrast, the content of malondialdehyde (MDA) increased with increasing dietary protein levels and reaching a maximum in the 52% protein group, suggesting that MDA accumulation depends on the protein concentration and the potential oxidative stress. Taken together, based on the broken-line analysis of SGR, we recommended the optimum dietary protein for C. mongolicus fingerlings to be 48.97%~49.31%.

Moringa oleifera Leaves' Extract Enhances Nonspecific Immune Responses, Resistance against Vibrio alginolyticus, and Growth in Whiteleg Shrimp (Penaeus vannamei)

Simple Summary

This study found that moringa (Moringa oleifera) leaves’ water extract triggered phenoloxidase activity, phagocytic rate, and superoxide anion production in whiteleg shrimp (Penaeus vannamei) hemocytes by an in vitro assay. By an in vivo assay, a dietary moringa extract enhanced the total hemocyte count, phenoloxidase activity, phagocytic rate, immune-related gene expressions, and growth performance of the whiteleg shrimp. The administration of dietary moringa extract increased the survival rate after challenging the whiteleg shrimp with Vibrio alginolyticus.

Abstract

Moringa is widely known as a plant with high medicinal properties. Therefore, moringa has a high potential for use as an immunostimulant in shrimp. This study investigated the effect of a moringa water extract on the immune response, resistance against V. alginolyticus, and growth performance of whiteleg shrimp. To perform the in vitro assay, hemocytes were incubated with different concentrations of the moringa extract. Furthermore, the moringa extract was incorporated at 0 (control), 1.25 g (ME1.25), 2.5 g (ME2.5), and 5.0 g (ME5.0) per kg of diet for the in vivo assay. During the rearing period, immune responses, namely the total hemocyte count (THC), phenoloxidase (PO) activity, phagocytosis activity, superoxide anion production, and immune-related gene expression were examined on days 0, 1, 2, 4, 7, 14, 21, and 28. Growth performance was measured 60 days after the feeding period. Furthermore, the shrimp were challenged with V. alginolyticus after being fed for different feeding durations. The results of the in vitro assay revealed that 100–250 ppm of the moringa extract enhanced the PO activity, phagocytic rate (PR), and superoxide anion production. The findings of the in vivo assay demonstrated that the THC, PO activity, PR, and immune-related gene expression, including alpha-2-macroglobulin, prophenoloxidase II, penaeidin2, penaeidin3, anti-lipopolysaccharide factor, crustin, lysozyme, superoxide dismutase, and clotting protein, were higher in the group of ME.25 and ME5.0 than in the control and ME1.25 at several time points. Growth performance was significantly increased (p < 0.05) in the ME2.5 group compared to the control group. Furthermore, the dietary ME2.5 resulted in a higher survival rate compared to that of the control group after challenging with V. alginolyticus, especially at ME2.5 administered for 4 and 7 days. This study indicated that the incorporation of the moringa extract at 2.5 g per kg of diet enhanced the immune response, the growth performance of the whiteleg shrimp, and the resistance against V. alginolyticus infection.

Immunotoxicity of polychlorinated biphenyls (PCBs) to the marine crustacean species, Scylla paramamosain

Polychlorinated biphenyls (PCBs) are persistent organic pollutants in environments, and they can negatively affect aquatic animal health. After 7 days of PCBs exposure, the activities of catalase, phenoloxidase, and superoxide dismutase and the total hemocyte count in the haemolymph were significantly decreased and the reactive oxygen species (ROS) content and phagocytic rate of hemocytes were significantly increased in mud crab Scylla paramamosain. Additionally, serum lysozyme, glutathione, glutathione-S-transferase, and glutathione peroxidase activities were significantly down-regulated in mud crab after PCBs exposure. The survival rate of crab hemocytes significantly declined as the PCBs concentration increased, indicating that PCBs had a cytotoxic effect on hemocytes. Exposure to increasing concentrations of PCBs also increased the degree of DNA damage in crab hemocytes. After PCBs exposure, the expression levels of P53 and caspase-3 in hemocytes were significantly up-regulated, which suggests that apoptosis was occurring. The apoptosis rate of hemocytes was up-regulated as the PCBs concentration increased, indicating that apoptosis was induced by the PCBs-activated caspase-3 pathway. These data suggest that exposure to PCBs hampered the immune response of mud crabs, most likely by (1) inducing ROS, causing DNA damage, and reducing the viability of hemocytes, (2) reducing the activities of antioxidant enzymes, and (3) inducing phagocytosis and apoptosis of hemocytes. And the final result of PCBs-induced immunotoxicity to mud crabs is the reduced bacterial disease resistance and survival rate of crabs under Vibrio alginolyticus challenge.

β-1,3-Glucan from Euglena gracilis as an immunostimulant mediates the antiparasitic effect against Mesanophrys sp. on hemocytes in marine swimming crab (Portunus trituberculatus)

β-1,3-glucans, natural polysaccharide groups, exert immunomodulatory effects to improve the innate response and disease resistance in aquatic species and mammals. However, this β-glucan stimulant is yet to be assayed in swimming crab (Portunus trituberculatus) hemocytes. In this study, we explored the immunomodulatory effect of β-1,3-glucans (derived from Euglena gracilis) via in vitro 24 h stimulation assays in swimming crab hemocytes. We found that this algal β-1,3-glucans in crab hemocytes significantly elevated cellular enzymes related parameters, including phenoloxidase (PO), lysozyme, acid phosphatase (ACP) activities, and superoxide anion generation (O₂^-) rate both at intracellular (P < 0.05) and extracellular (P < 0.05) levels. Besides, alkaline phosphatase (AKP) in hemocytes exhibited no significant differences across the groups (P > 0.05). β-glucan significantly influenced (P < 0.05) the activities of the antioxidant enzyme, superoxide dismutase (SOD) in hemocytes. Moreover, the relative mRNA expression of numerous immune-related genes, including proPO, TLR-2, Alf-1, NOX, Lysozyme, Crustin-1, and Cuznsod, was significantly higher stimulated hemocytes than in control (P < 0.05). We also reported the dose-dependent antiparasitic activity against Mesanophyrs sp., in stimulated hemocytes than in the control (P < 0.05). The present study collectively demonstrated that β-glucan potentially stimulates innate immunity by elevating cellular enzyme responses and up-regulating the mRNA expression of genes associated with crab innate immunity. Thus, β-glucan is a promising immunostimulant for swimming crab farming in crustaceans aquaculture.

Nannochloropsis spp. as Feed Additive for the Pacific White Shrimp: Effect on Midgut Microbiology, Thermal Shock Resistance and Immunology

This work aimed to evaluate Nannochloropsis spp. as feed additive in the diet of Pacific white shrimp for their effect on midgut microbiology, thermal shock resistance and immunological parameters. Initially, the digestibility of the microalgae meal was assessed, and the apparent digestibility coefficient (ADC) was determined. The ADC was, in general, high in lipids (78.88%) and eicosapentaenoic fatty acid (73.86%). Then, Nannochloropsis spp. were included in diets at four levels (0, 0.5, 1 and 2% inclusion). The shrimp were reared in 500 L clear water tanks containing 20 shrimp per tank with an initial weight of 6.05 ± 0.06 g and fed four times a day. Shrimp fed with supplemented diets containing Nannochloropsis spp. (0.5 and 2%) presented higher resistance to thermal shock when compared to the non-supplemented group (control). Shrimp fed with 1 and 2% of algae inclusion had a higher production of reactive oxygen species (ROS) when compared to other treatments. No statistical difference was observed in the immunological parameters and microbiology of the intestinal tract. Thus, the inclusion of Nannochloropsis spp. in shrimp diets at 0.5 and 2% levels increases resistance to thermal shock and ROS production in shrimp.

Immune response and oxidative stress of shrimp Litopenaeus vannamei at different moon phases

Moon phases influence the molting process of shrimp, which affect other physiological processes as immune response. This study analyzed some parameters of immune response: total hemocytes counts (THC), hemolymph clotting time and superoxide anion (O₂^-) production, total protein concentration, superoxide dismutase activity, and the presence of Vibrio spp. in Litopenaeus vannamei at different moon phases. The highest percentage of organisms in intermolt stage was observed in the first quarter moon phase (95%). The highest THC was observed at new moon phase, which was significantly different (p < 0.05) than that observed at the third quarter phase. Hemolymph clotting time and CFU values of Vibrio spp. showed no significant difference (p > 0.05) between different moon phases. The higher (p < 0.05) mean O₂^- production value (0.400 ± 0.168 nmol min^-1 mL^-1) was determined in hepatopancreas at new moon phase. No relationship was observed between O₂^- and SOD activity, indicating that this antioxidant response was enough to counteract the influence of oxidative stress in L. vannamei at different moon phases.

Dietary supplementation of marine yeast Yarrowia lipolytica modulates immune response in Litopenaeus vannamei

The immunostimulatory potential of the marine yeast Yarrowia lipolytica (D1 and N6 strains) administered orally was evaluated in the white shrimp Litopenaeus vannamei. Yeasts and commercial glucans were mixed with a commercial feed to formulate diets with a 1.1% concentration of immunostimulants. The shrimp were fed daily for a period of 21 days. Weekly determinations were performed for immunological parameters in hemolymph, such as total hemocyte count (THC), lysozyme activity (LYZ), prophenoloxidase activity, antioxidant enzymatic activities (superoxide dismutase [SOD], catalase [CAT], and peroxidases), and bactericidal activity against Vibrio parahaemolyticus. Expression profiles of penaeidin (PEN), lysozyme (LYZ), and prophenoloxidase (proPO) immune genes were evaluated in hemocytes. In general, an increase in the immune parameters was observed in shrimp fed yeast diet compared to glucan and the control diets. Yarrowia lipolytica, especially strain N6, provided maximum immunostimulatory effects evidenced by the increase of immune parameters (THC, LYZ, SOD, CAT) and gene expression profile. In conclusion, this study demonstrated that Y. lipolytica had immunostimulatory effects and increased bactericidal activity in L. vannamei hemocytes against V. parahaemolyticus. These findings open the path for the potential application of Y. lipolytica-based immunostimulant for shrimp aquaculture.

Role of novel protein kinase C in neuroendocrine-immune regulatory network in haemocytes of Litopenaeus vannamei: An in vitro approach

Shrimp lack adaptive immune systems and mainly rely on the cellular and humoral defences, involving the haemocytes (functionally analogous to vertebrate leukocytes) in non-self matter recognition, elimination, and in downstream coagulation. Furthermore, the linkage between stress-induced catecholamine (CA), a class of biogenic amines (BAs), releasing and immunological responses has been detected in shrimp. Varied isotypes of protein kinase C (PKC) regulate multiple cellular processes following their specific location and distribution within the cells, and a novel PKC identified in Litopenaeus vannamei (termed as LvnPKC) is proposed to mediate signaling transduction of immunocompetence and BA biosynthesis. In the present study, we analyzed the effects of the LvnPKC-silenced haemocytes by co-incubating with its dsRNA on the immune responses specific to prophenoloxidase (proPO) and antioxidant systems as well as phagocytic activity. In addition, the capability of haemocytes to produce BAs was assessed. The results revealed that LvnPKC-silenced haemocytes can induce interference in phenoloxidase and superoxide dismutase activities, respiratory bursts, and phagocytic activity; meanwhile, the disturbed gene expressions of proPO activating enzyme, proPOII, lipopolysaccharide- and β-1,3-glucan-binding protein, and cytosolic manganese superoxide dismutase were detected. The same deviated pattern was observed in tyrosine, dopamine, and norepinephrine levels, and in dopamine β-hydroxylase (DBH) activity and gene expressions of tyrosine hydroxylase, DOPA decarboxylase, and DBH involving in BA biosynthesis. Taken together, these results suggest that the immunocompetence and BA biosynthesis of haemocytes can be mediated via LvPKC signaling transduction, which proved the presence of a neuroendocrine-immune regulatory network in haemocytes.

Differentially proteomic analysis of the hemocytes against Aeromonas hydrophila infection in oriental river prawn Macrobrachium nipponense by iTRAQ approach

As the direct executors of biological function, the expression level of proteins in host will reveal the molecular mechanisms regulating bacteria infection more directly. In the present study, the differential proteomes of Macrobrachium nipponense hemocytes response to Aeromonas hydrophila infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography electrospray ionization tandem mass spectrometry. The hemocyte proteins from the unchallenged and A. hydrophila challenged prawn, M. nipponense, at 12, 24 and 36 h post infection were compared. From this, a total of 3372 proteins were identified and 1014 proteins were considered differentially expressed, of which 117 common differentially expressed proteins were indicated between the time points. Hierarchical clustering, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes enrichment and protein-protein interaction network analyses were performed for the general characterization of overall enriched proteins. Cytoskeletal proteins including myosin heavy chain, myosin regulatory light chain, actin, tubulin alpha/beta chain, troponin I and troponin T as well as antioxidant enzymes such as catalase and cytosolic MnSOD were found significantly up-regulated in hemocytes, indicating that the phagocytosis process and ROS system were induced after challenge with A. hydrophila. And other proteins such as integrin β, innexin inx2-like and heat shock protein 60 also participate in prawn immune response against bacteria. Parallel reaction monitoring analyses were carried out for validation of the expression levels of differentially expressed proteins, which indicated high reliability of the proteomic results. This is the first report on proteome of M. nipponense hemocytes against A. hydrophila infection, which contributes to better understanding on the molecular mechanisms of prawns.

Dietary Hizikia fusiforme enhance survival of white spot syndrome virus infected crayfish Procambarus clarkii

The sea vegetable Hizikia fusiforme is not only a good source of dietary fiber but also enhances immunity. In this study, we investigated the effects of H. fusiforme on innate immunity in invertebrates, using white spot syndrome virus (WSSV) challenge in the crayfish, Procambarus clarkii. Supplementation with H. fusiforme significantly reduced mortality caused by WSSV infection and also reduced copy numbers of the WSSV protein VP28. Quantitative reverse transcription-polymerase chain reaction showed that supplementation of feed with H. fusiforme increased the expression of immune-related genes, including NF-κB and crustin 1. Further analysis showed that supplementation with H. fusiforme also affected three immune parameters, total hemocyte count, and phenoloxidase and superoxide dismutase activity. H. fusiforme treatment significantly increased hemocyte apoptosis rates in both WSSV-infected and uninfected crayfish. H. fusiforme thus regulates the innate immunity of crayfish, and both delays and reduces mortality after WSSV challenge. Our study demonstrates the potential for the commercial use of H. fusiforme, either therapeutically or prophylactically, to regulate the innate immunity and protect crayfish against WSSV infection.

Dietary Bacillus amyloliquefaciens enhance survival of white spot syndrome virus infected crayfish

Bacillus amyloliquefaciens, which is closely related to Bacillus subtilis, produces a series of metabolites that can inhibit the growth of fungi and bacteria. Here, we investigated the effect of B. amyloliquefaciens used as a probiotic on the innate immunity of the crayfish Procambarus clarkii when challenged with white spot syndrome virus (WSSV). Dietary B. amyloliquefaciens supplement significantly reduced the mortality of WSSV-challenged crayfish and reduced copy numbers of WSSV. The quantitative reverse transcription-polymerase chain reaction results showed that B. amyloliquefaciens supplement increased the expression of several immune-related genes, including Toll-like receptor, NF-κB and C-type-lectin. Further analysis showed that B. amyloliquefaciens supplement also had an effect on three immune parameters, including total hemocyte count, phenoloxidase activity and superoxide dismutase activity. In both infected and uninfected crayfish, B. amyloliquefaciens supplement significantly decreased hemocyte apoptosis. Our results showed that B. amyloliquefaciens can regulate innate immunity of crayfish and reduce the mortality following WSSV challenge. This study provides a novel insight into the potential for therapeutic or prophylactic intervention with B. amyloliquefaciens to regulate crayfish immunity and protect against WSSV infection, and also provides a theoretical basis for the use of probiotics as aquatic feed additives.

Effects of hesperidin on the growth performance, antioxidant capacity, immune responses and disease resistance of red swamp crayfish (Procambarus clarkii)

We evaluated the effects of hesperidin on the nonspecific immunity, antioxidant capacity and growth performance of red swamp crayfish (Procambarus clarkii). A total of 900 healthy crayfish were randomly divided into six groups: the control group (fed the basal diet) and the HES25, HES50, HES75, HES100 and HES150 groups, which were fed the basal diet supplemented with 25, 50, 75, 100 and 150 mg kg^-1 hesperidin, respectively. The feeding experiment lasted 8 weeks. The results indicated that compared with the control group, the crayfish groups supplemented with 50-150 mg kg^-1 hesperidin had a decreased feed conversion ratio (FCR) and increased final body weight (FBW), specific growth rate (SGR) and weight gain (WG) (P < 0.05). The protein carbonyl content (PCC), reactive oxygen species (ROS) level and malondialdehyde (MDA) level in the hepatopancreas and hemocytes were significantly lower, while the total antioxidant capacity (T-AOC), glutathione peroxidase (GPx) activity, and superoxide dismutase (SOD) activity were significantly higher in the crayfish groups supplemented with 50-150 mg kg^-1 hesperidin than in the control group. Supplementation with 50-150 mg kg^-1 hesperidin significantly increased the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), lysozyme (LZM), and phenoloxidase (PO) compared with the control group (P < 0.05); upregulated the mRNA expression of cyclophilin A (CypA), extracellular copper-zinc superoxide dismutase (ecCuZnSOD), GPxs, crustin, astacidin, Toll3 and heat shock protein 70 (HSP70) (P < 0.05); and decreased crayfish mortality following white spot syndrome virus (WSSV) infection. These findings indicate that dietary hesperidin supplementation at an optimum dose of 50-150 mg kg^-1 may effectively improve nonspecific immunity, antioxidant capacity and growth performance in crayfish.

MMP-14 regulates innate immune responses to Eriocheir sinensis via tissue degradation

Matrix metalloproteinases (MMPs) are a cluster of enzymes that degrade the extracellular matrix (ECM) and some intracellular proteins; as such, they play an important role in tissue regeneration, infant growth, animal reproduction, and immunity. Most research into MMPs focuses mainly on their effects on the mammalian immune system. However, it is not clear how MMPs affect immune processes in crustaceans. Here, we cloned the open reading frame (ORF) of Eriocheir sinensis (Chinese mitten crab) MMP-14 (EsMMP-14) to explore the role of MMPs in crustacean innate immune responses. RT-PCR results showed that stimulation of crab with LPS and poly I:C upregulated expression of EsMMP-14 markedly. Besides, following the stimulation of 20-Hydroxyecdysone, the expression level of EsMMP-14 increased robustly, suggesting that EsMMP-14 involved in the molt process of E. sinensis. Hematoxylin and eosin staining of hepatopancreas and intestine revealed that knocking down EsMMP-14 maintained morphology following infection by Bacillus thuringiensis. Moreover, downregulated expression of EsMMP-14 increased the survival rate of infected E. sinensis. These results show that EsMMP-14 plays a role in innate immune responses of E. sinensis and fills a gap in our knowledge about the function of MMPs in crustaceans.

The role of Astakine in Scylla paramamosain against Vibrio alginolyticus and white spot syndrome virus infection

Astakine is a crucial factor in the proliferation and differentiation of hematopoietic stem cells and is directly involved in hematopoiesis in crustaceans. To assess the role of Astakine in the innate immune system of Scylla paramamosain, the immune responses in healthy and Astakine-inhibited S. paramamosain were investigated in the present study. The RNA transcripts of Astakine were widely distributed in all examined tissues, with significantly higher levels of expression in hemocytes of both healthy and challenged S. paramamosain with Vibrio alginolyticus and WSSV. When Astakine was knocked down by RNA interference technology, immune-related genes, including Janus kinase, prophenoloxidase, hemocyanin, β-actin, myosin II essential light chain-like protein, signal transducer and activator of transcription, Relish, and C-type-lectin, were significantly down-regulated in hemocytes. The levels of phenoloxidaseactivity (PO), total hemocyte counts (THC) and hemocyte proliferation decreased significantly in hemocytes of Astakine-dsRNA treated S. paramamosain. After being challenged with V. alginolyticus and WSSV, the THC decreased significantly and the levels of hemocyte apoptosis increased significantly in Astakine-dsRNA treated S. paramamosain in comparison with those in infected groups without Astakine-dsRNA treatment. After being challenged with WSSV, the WSSV copies were significantly lower in Astakine-dsRNA treated groups than those in the WSSV infection group, which suggested that knockdown of Astakine was not conductive to WSSV replication and this might be associated with the decreasing THC. The results of survival analysis showed that the survival rate of V. alginolyticus or WSSV infected S. paramamosain decreased significantly following Astakine knockdown. These results suggested that RNA interference of Astakine might weaken the resistance of S. paramamosain to V. alginolyticus or WSSV infection. The weaken resistivity after knockdown Astakine might be related to the changes of important immune-related gene expression, THC, PO activity, proliferation and apoptosis of hemocytes.

Immunization of a novel bivalent outer membrane protein simultaneously resisting Aeromonas hydrophila, Edwardsiella anguillarum and Vibrio vulnificus infection in European eels (Angullia angullia)

In cultivated European eels, Aeromonas hydrophila, Edwardsiella anguillarum and Vibrio vulnificus are three important bacterial pathogens. In this study, European eels (Anguilla anguilla) were immunized by the bivalent expression products of the outer membrane protein (Omp) gene from A. hydrophila (OmpⅡ) and E. anguillarum (OmpA), and the effects of the bivalent protein (rOmpⅡ-A) on the immune function of the European eel were detected. Three hundred eels were divided average into three groups of PBS, adjuvant and rOmp. Eels of three goups were injected intraperitoneal with 0.2 mL of PBS (0.01 mol/L, pH7.4), PBS + F (PBS mixed equal volume of freund's uncomplete adjuvant) or rOmpⅡ-A (1 mg mL^-1 rOmpⅡ-A mixed equal volume of freund's uncomplete adjuvant). Four immune-related genes expression, proliferation of whole blood cells, serum and skin mucus antibody titer, superoxide dismutase (SOD) activity and the relative percent of survival (RPS) were studied at different days (or hours) post the immunization. The results showed that the igm, lysC, mhc2 and sod gene in the liver, spleen, kidney and intestine tract were significant increased in the Omp group; On the 28 day post the immunization (dpi), blood cell proliferation was increased in the Omp group, and on the 14, 21, 28 and 42 dpi, antibody titers in serum and mucus of the Omp group were significantly higher than that of the PBS and adjuvant group, regardless of coating with bacteria or Omp antigen. The SOD activity of Omp group increased significantly in liver, kidney, skin mucus and serum from 14 to 42 dpi, especially in serum. Eels chanllenged by A. hydrophila, E. anguillarum and V. vulnificus in the bivalent Omp group showed the RPS were 83.33%, 55.56% and 44.44%, respectively. The results of this study showed that immunization of the bivalent Omp could effectively improve the immune function of European eels, and produced effectively protection to A. hydrophila and E. anguillarum infection. Simultaneously, the bivalent Omp also produced distinct cross-protection to the eels challenged by V. vulnificus.

Novel protein kinase C participates catecholamine biosynthesis and immunocompetence modulation in haemocytes of Litopenaeus vannamei

The catecholamine biosynthesis is required for physiological and immunological responses against stress, and the neuroendocrine-immune regulatory network plays a crucial role in immunocompetence of shrimp. A novel protein kinase C of Litopenaeus vannamei (LvnPKC) is involved in immune defense and signaling transduction in haemocytes, and in the present study, the gene silence technique is conducted to identify the role of LvnPKC on catecholamine biosynthesis and immunocompetence modulation in haemocytes of L. vannamei. The results show that tyrosine significantly increases in haemocytes of LvnPKC-silenced shrimp, and in the meantime, the obvious decrease of L-3, 4-dihydroxyphenylalanine and increase of dopamine as well as the consistent norepinephrine levels are detected. Tyrosine hydroxylase and dopamine β-hydroxylase activities are significantly reduced in haemocytes of LvnPKC-silenced shrimp. Total haemocyte count, hyaline cells and granulocytes insignificantly differ among treatments, and the obvious increase of phenoloxidase activity, respiratory bursts, superoxide dismutase and glutathione peroxidase activities are observed in haemocytes of LvnPKC-silenced shrimp, and furthermore, the downregulated phagocytic activity was observed. It is therefore concluded that the LvnPKC mediates catecholamine biosynthesis and immunocompetence in haemocytes, and plays a crucial role in the neuroendocrine-immune regulatory network.

Immunization of a novel outer membrane protein from Aeromonas hydrophila simultaneously resisting A. hydrophila and Edwardsiella anguillarum infection in European eels (Angullia angullia)

In cultivated European eels, Aeromonas hydrophila, Edwardsiella anguillarum and Vibrio vulnificus are three important bacterial pathogens. In this study, an expressed recombinant Outer membrane proteinⅡ (rOmpⅡ) from A. hydrophila was intraperitoneally injected into European eels (Angullia angullia). All examined eels were equally divided into three groups. One group was injected with PBS only (PBS group), one group was injected with 1:1 mixture of PBS and Freund's incomplete adjuvant (PBS + F, adjuvant group), and the third group was injected with 1:1 mixture of 1 mg mL^-1 rOmpⅡ and Freund's incomplete adjuvant (rOmpⅡ+F, OmpⅡ group). The immunogenicity of OmpⅡ was studied by detecting the expression of 4 immune-related genes, stimulation index (SI) of the whole blood cell, serum antibody titer, lysozyme and Superoxide Dismutase (SOD) activity, and relative percent of survival (RPS) rate. The results showed that gene expression of MHC-Ⅱ, LysC, SOD and IgM in the OmpⅡ group significantly increased in liver, spleen, kidney and intestine. At 28 days post the immunization (dpi), the SI of whole blood cells in the OmpⅡ group increased significantly; at 14, 21, 28 and 42 dpi, the serum antibody titers against A. hydrophila and E. anguillarum in the OmpⅡ group were significantly higher than that of the PBS and the adjuvant group; the SOD in the OmpⅡ group was found increased significantly in liver, kidney, mucus and serum. On the 28 dpi, eels were challenged by A. hydrophila, E. anguillarum and V. vulnificus for cross protection study. The results showed that the RPS of the OmpⅡ group were 83.33%, 55.56% and 33.33% respectively. These results showed that the expressed OmpⅡ from A. hydrophila significantly improve the immune function of Europena eels and their resistance to the infection of A. hydrophila and E. anguillarum simultaneously.

Effects of palytoxins extracted from Ostreopsis ovata on the oxidative stress and immune responses in Pacific white shrimp Litopenaeus vannamei

Palytoxins (PLTXs) are a group of complex and poisonous marine natural products that are toxic to marine life and even human beings. In the present study, the oxidative stress and immune response in the hepatopancreas and gills of Litopenaeus vannamei were assessed for 72 h after injection with PLTX extracts. Chemical and physiological parameters, e.g., the respiratory burst (O₂^-), activities of antioxidant enzymes, oxidative damage to lipids, carbonylation of proteins, and immune gene mRNA expression levels, were analysed. The results showed that the PLTX extract was not fatal to the shrimp but could reduce their mobility. The O₂^- levels in the gills gradually increased after exposure to PLTX extracts and were significantly higher than those in the control from 6 to 72 h. The malondialdehyde content, lipid peroxidation, protein carbonyl levels, and total antioxidant capacity in the gills all peaked at 12 h. At the same time, the gills were loosely connected, there was a clear disintegration of the epithelial tissue, and the stratum corneum disappeared after 12 h. In addition, compared to those in the control group, the PLTX extract treatment increased the O₂^- content, malondialdehyde content, lipid peroxidation, and protein carbonyl levels from 12 to 72 h, 24-48 h, 12-24 h, and 12-72 h after injection in the hepatopancreas of the shrimp, respectively. Both the Crustin and Toll gene expression levels significantly increased in the hepatopancreas compared to those in the control 6-72 h after injection of the toxin. In parallel, the expression levels of the manganese superoxide dismutase gene gradually decreased from 6 to 48 h and returned to normal levels after 72 h. Interestingly, the total antioxidant capacity also significantly increased compared to that in the control from 6 to 72 h. Our results indicate that although PLTX extracts cause lipid peroxidation and carbonylation of proteins in hepatopancreatic cells, leading to their damage, they did not cause a decrease in the total antioxidant capacity of the hepatopancreas.

Molecular characterization of carboxypeptidase B-like (CPB) in Scylla paramamosain and its role in white spot syndrome virus and Vibrio alginolyticus infection

Carboxypeptidase plays an important physiological role in the tissues and organs of animals. In this study, we cloned an entire 2316 bp carboxypeptidase B-like (CPB) sequence with a 1302 bp open reading frame encoding a 434 amino acid peptide from Scylla paramamosain. The CPB gene was expressed highly in hepatopancreas and decreased in crab hemocytes after challenges with white spot syndrome virus (WSSV) or Vibrio alginolyticus. After CPB gene knockdown using double-stranded RNA (CPB-dsRNA), the expression of JAK, STAT, C-type lectin, crustin antimicrobial peptide, Toll-like receptors, prophenoloxidase, and myosin II essential light chain-like protein were down-regulated in hemocytes at 24 h post dsRNA treatment. CPB knockdown decreases total hemocyte count in crabs indicated that CPB may negatively regulate crab hemocyte proliferation in crabs. CPB showed an inhibitory effect on hemocyte apoptosis in crabs infected with WSSV or V. alginolyticus. The phagocytosis rate of WSSV by hemocytes was increased after CPB-dsRNA treatment. After WSSV challenge, the mortality and WSSV copy number were both decreased but the rate of hemocyte apoptosis was increased in CPB-dsRNA-treated crabs. The results indicate that the antiviral activity of the crabs was enhanced when CPB was knocked down, indicating WSSV may take advantage of CPB to benefit its replication. In contrast, the absence of CPB in crabs increased mortality following the V. alginolyticus challenge. The phagocytosis rate of V. alginolyticus by hemocytes was increased after CPB-dsRNA treatment. It was revealed that CPB may play a positive role in the immune response to V. alginolyticus through increasing the phagocytosis rate of V. alginolyticus. This research further adds to our understanding of the CPB and identifies its potential role in the innate immunity of crabs.

Effects of short-term fasting on the resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus agalactiae infection

Short-term feed deprivation or fasting is commonly experienced by aquaculture fish species and may be caused by seasonal variations, production strategies, or diseases. To assess the effects of fasting on the resistance of Nile tilapia to Streptococcus agalactiae infection, vaccinated and unvaccinated fish were fasted for zero, one, three, and seven days prior to infection. The cortisol levels of both vaccinated and unvaccinated fish first decreased and then increased significantly as fasting time increased. Liver glycogen, triglycerides, and total cholesterol decreased significantly after seven days of fasting, but glucose content did not vary significantly between fish fasted for three and seven days. Hexokinase (HK) and pyruvate kinase (PK) activity levels were lowest after seven days of fasting, while phosphoenolpyruvate carboxykinase (PEPCK) activity levels varied in opposition to those of HK and PK. Serum superoxide dismutase (SOD) and catalase (CAT) activity levels first increased and then decreased as fasting time increased; SOD activity was highest after three days of fasting. Interleukin-1beta (IL-1β) and IL-6 mRNA expression levels first increased and then decreased significantly, peaking after three days of fasting. However, suppressor of cytokine signaling-1 (SOCS-1) mRNA expression levels were in opposition to those of IL-1β and IL-6. Specific antibody levels did not vary significantly among unvaccinated fish fasted for different periods. Although specific antibody level first increased and then decreased in the vaccinated fish as fasting duration increased, there were no significant differences in the survival rates of fasted vaccinated fish after challenge with S. agalactiae. The final survival rates of vaccinated fish fasted for zero, one, three, and seven days were 86.67 ± 5.44%, 80.00 ± 3.14%, 88.89 ± 6.28%, and 84.44 ± 8.32%, respectively. Among the unvaccinated fish, the survival rate was highest (35.56 ± 3.14%) in the fish fasted for three days and lowest (6.67 ± 3.14%) in the fish fasted for seven days. Therefore, our results indicated that short-term fasting (three days) prior to an infection might increase the resistance of unvaccinated Nile tilapia to S. agalactiae.

Effects of dietary yeast hydrolysate on the growth, antioxidant response, immune response and disease resistance of largemouth bass (Micropterus salmoides)

A 56-day growth trial was conducted to investigate the effects of dietary yeast hydrolysate on the growth performance, antioxidation, immune response and resistance against Aeromonas hydrophila in largemouth bass. Four experimental diets were prepared with yeast hydrolysate levels of 0% (Y0), 1.5% (Y1.5), 3.0% (Y3.0) and 4.5% (Y4.5). Each diet was randomly assigned to triplicate 150-L tanks and each tank was stocked with 30 largemouth bass (initial body weight, IBW = 7.71 ± 0.02 g). A challenge test was carried out after the feeding trial by injecting A. hydrophila intraperitoneally for 4-day observation. The results showed that the FBW and WGR in Y1.5 group were significantly higher than those in Y0 group (P < 0.05) and the feed conversion ratio (FCR) got the lowest value in Y1.5 group. And the hydrolysate supplement significantly increased the 4-day cumulative survival rate after the bacterial challenge (P < 0.05). The plasma malondialdehyde was lower in the yeast hydrolysate supplement groups in both pre- and post-challenge test (P < 0.05), while the plasma C3 increased (P < 0.05). In post-challenge test, the plasma superoxide dismutase (SOD) and catalase (CAT) activities increased in the Y1.5 and Y3.0 groups respectively (P < 0.05), and plasma lysozyme in Y1.5 group and the plasma IgM in Y3.0 group were higher than those in others respectively (P < 0.05). For the q-PCR results, in post-challenge test, the hepatic hep2 expression level in Y1.5 and Y4.5 groups were both significantly higher than those in others (P < 0.05), as well as il-8 in Y3.0 group. The spleen hif-1alpha and tgf-beta1 expression levels in Y4.5 group were all significantly lower than those in others (P < 0.05), while the gilt was significantly higher (P < 0.05) in the post-challenge test. And the expression levels of spleen tnf-alpah1 in Y1.5 and Y3.0 groups and il-8 in Y3.0 group were all significantly higher than those in other groups (P < 0.05) in the post-challenge test. The head kidney gilt expression level was significantly higher in the yeast hydrolysate supplement groups compared with the Y0 group (P < 0.05), and the head kidney il-8 expression level in Y1.5 group was significant higher than those in other groups in post-challenge test (P < 0.05). The present results indicated dietary yeast hydrolysate improved the antioxidant ability and enhanced the immune response of largemouth bass without negative effect on growth. And 1.5% or 3.0% of dietary yeast hydrolysate was recommended for largemouth bass based on the present results.

Hesperetin protects crayfish Procambarus clarkii against white spot syndrome virus infection

Hesperetin is a natural flavanone compound, which mainly exists in lemons and oranges, and has potential antiviral and anticancer activities. In this study, hesperetin was used in a crayfish pathogen challenge to discover its effects on the innate immune system of invertebrates. The crayfish Procambarus clarkii was used as an experimental model and challenged with white spot syndrome virus (WSSV). Pathogen challenge experiments showed that hesperetin treatment significantly reduced the mortality caused by WSSV infection, while the VP28 copies of WSSV were also reduced. Quantitative reverse transcriptase polymerase chain reaction revealed that hesperetin increased the expression of several innate immune-related genes, including NF-kappaB and C-type lectin. Further analysis showed that hesperetin treatment plays a positive effects on three immune parameters like total hemocyte count, phenoloxidase and superoxide dismutase activity. Nevertheless, whether or not infected with WSSV, hesperetin treatment would significantly increase the hemocyte apoptosis rates in crayfish. These results indicated that hesperetin could regulate the innate immunity of crayfish, and delaying and reducing the mortality after WSSV challenge. Therefore, the present study provided novel insights into the potential therapeutic or preventive functions associated with hesperetin to regulate crayfish immunity and protect crayfish against WSSV infection, provide certain theoretical basis for production practice.

Sea Surface Temperature Modulates Physiological and Immunological Condition of Octopus maya

Octopus maya is a valuable endemic species of the Yucatán Peninsula (YP). This area can be divided into distinct regions depending on the presence of cold waters associated to upwelling events during spring and summer. This study was designed to determine if the physiological and immunological condition of O. maya show a relationship with variation of the sea surface temperature associated with the seasonal upwelling. A total of 117 organisms were collected from February to July in three fishing zones: Ría Lagartos located in the upwelling zone; Seybaplaya corresponding to the non-upwelling zone, and Sisal, the transitional zone. The organisms were examined in terms of physiological (total weight, the weight of the gonad and digestive gland, osmotic pressure, hemocyanin, protein, glucose, and cholesterol concentrations in plasma), and immunological variables (total hemocyte count, hemagglutination, phenoloxidase system activity, total phenoloxidase plasma activity, and lysozyme activity). Multivariate one-way ANOVA showed overall significant differences between groups of octopus by month/zone of capture, indicating that the physiological-immunological condition of O. maya is related to a temperature gradient. Wild octopuses captured at the upwelling zone and the transitional zone (Ría Lagartos and Sisal) in February, March, and April -with temperatures lower than 27°C- were in better conditions: larger size, high concentrations of hemocyanin, and low activity of the phenoloxidase system. Octopuses captured in the warmer waters (28–30°C) of the non-upwelling and transitional zones (Seybaplaya and Sisal) during June and July, could be reflecting the metabolic stress through immunological compensation mechanisms with higher activity of the phenoloxidase system, despite having a lower concentration of hemocytes, hemocyanin, and proteins. Although the movement of individual O. maya along the YP throughout their life cycle has not yet been determined, direct development and benthic behavior could limit the mobility of the organisms in such a way that their physiological and immunological condition might reflect adaptation to the regional environment. This information could help understand the performance of octopuses in their distribution area, which sustains an important fishery.

Macrobrachium rosenbergii Cu/Zn superoxide dismutase (Cu/Zn SOD) expressed in Saccharomyces cerevisiae and evaluation of the immune function to Vibrio parahaemolyticus

Superoxide dismutases (SODs) are important antioxidant enzymes that occur in virtually all oxygen-respiring organisms, and copper/zinc SOD (Cu/ZnSOD) is one of the most important SODs. In the present study, Macrobrachium rosenbergii Cu/Zn-SOD was expressed in a yeast eukaryotic system. The open reading frame (ORF) of MrCu/ZnSOD was cloned into the plasmid vector pHAC181, and the recombinant plasmid was integrated into the downstream region of the GAL1 promoter in Saccharomyces cerevisiae strain GAL1-ScRCH1 via homologous recombination. The resulting recombinant MrCu/ZnSOD consisted of a 3 × HA-tag at its C-terminal. Via western blot, the molecular weight of the recombinant MrCu/ZnSOD was estimated at about 30 kDa. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of this recombinant MrCu/ZnSOD ranged from 0.556 to 0.840 μM, and from 0.967 to 2.015 μM, respectively. The recombinant MrCu/ZnSOD protein was able to agglutinate four Gram-negative bacterial strains, as well as two of three Gram-positive strains (except Staphylococcus aureus). This demonstrated that the recombinant protein possessed some antimicrobial activity against certain Gram-positive and Gram-negative bacteria. M. rosenbergii were fed with the recombinant yeast strain MrCu/ZnSOD for 4 weeks and then challenged with the most common crustacean pathogen, Vibrio parahaemolyticus. This group of prawns presented lower mortality, higher enzymatic activity, and higher expression of the mRNA of immune-related genes than that in the control groups. Taken together, these results suggest that MrCu/ZnSOD is an antioxidant enzyme and antimicrobial peptide involved in the crustacean innate immune system and offers protection to the host against pathogenic bacteria.

Exposure to acute ammonia stress influences survival, immune response and antioxidant status of pacific white shrimp (Litopenaeus vannamei) pretreated with diverse levels of inositol

The effect of acute ammonia challenge on survival, immune response and antioxidant status of Litopenaeus vannamei pretreated with diets containing different inositol levels was investigated. Shrimp (initial mean weight 0.40 ± 0.00 g) were randomly allocated in 18 tanks (30 shrimp per tank) and triplicate tanks were fed with a control diet without myo-inositol (MI) supplementation (242.6 mg inositol kg^-1 diet) or diets containing diverse levels of inositol (368.8, 459.7, 673.1, 993.8 and 1674.4  mg kg^-1 diet) as treatment groups for 8-week. Randomly selected 10 shrimp per tank (final mean weight approximately 11.1-13.8g) were exposed to ammonia stress (total ammonia-nitrogen, 60.21  mg L^-1) for 24 h after feeding trial. The results showed that after exposed to ammonia stress, survival rates of MI-supplemented groups were enhanced by 31-77% when compared with the control group. MI supplementation increased activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in plasma, and reduced its activities in hepatopancreas. It also enhanced activities of total antioxidant capacity (T-AOC), glutathione S-transferase (GST) and glutathione peroxidase (GPX) and content of reduced glutathione (GSH), and lowered malondialdehyde (MDA) and protein carbonyl (PC) content in plasma or hepatopancreas. In addition, mRNA expression levels of ferritin (FT), arginine kinase (AK), thioredoxin (Trx), heat shock protein 70 (Hsp70), catalase (CAT) and peroxiredoxin (Prx) were significantly differentially regulated in hepatopancreas owing to MI supplementation. Therefore, it suggested that L. vannamei pretreated with higher dietary inositol content may have better ammonia stress tolerance and antioxidant status after ammonia stress, and the optimum levels ranged from 459.7 to 993.8 mg inositol kg^-1 when total ammonia-nitrogen concentration was 60.21  mg L^-1.

Feeding-regimen of β-glucan to enhance innate immunity and disease resistance of Nile tilapia, Oreochromis niloticus Linn., against Aeromonas hydrophila and Flavobacterium columnare

β-glucan is one of the most potent immunostimulants enhancing innate immune activity, disease resistance and growth performance of many aquatic organisms. Nevertheless, there are few studies on feeding regimens of β-glucan that correlate to immune response and disease resistance and are important considerations for practical β-glucan utilization. Thus, the effect of β-glucan and feeding duration on innate immunity and disease resistance was investigated to establish an optimal feeding regimen of β-glucan for Nile tilapia (Oreochromis niloticus Linn.). A variety of β-glucan feeding regimens were evaluated, including: i) feeding for 2 weeks, ii) feeding for 4 weeks, and iii) feeding every-other-week, with the objective of establishing the optimal feeding regimen that enhanced innate immunity and disease resistance. Innate immunity parameters were determined every week for eight weeks. Alternative complement activity of all β-glucan groups was significantly (P < 0.05) increased at the end of the first week, and then fluctuated but was not significantly (P > 0.05) different to the control until the end of the trial. Increased lysozyme activity was only detected at the end of the second week in all β-glucan-treated groups, and then decreased to the control level during most of the sampling periods. Phagocytosis percentage was increased and prolonged by β-glucan feeding, while the phagocytic index was not. Apart from innate immunity, β-glucan-fed fish demonstrated enhanced disease resistance against Aeromonas hydrophila and Flavobacterium columnare challenge at only the end of the fourth week of the trial. The growth performance of β-glucan-fed fish was not significantly (P > 0.05) different among the experimental groups and control. Taken together, the result indicated that all β-glucan-feeding regimens resulted in quite similar outcomes with respect to innate immunity stimulation, disease resistance and growth performance. This novel result suggests that an every-other-week regimen is the optimal choice for Nile tilapia cultivation as an economic cost saving benefit. This is the first study to determine the optimal feeding-regimen of β-glucan to enhance innate immunity and increase resistance to infection by pathogenic bacteria in Nile tilapia.

Gold nanoparticles (AuNP) exert immunostimulatory and protective effects in shrimp (Litopenaeus vannamei) against Vibrio parahaemolyticus

Gold nanoparticles (AuNP) stimulate immune responses in mammals but they have not been tested in species of relevance in aquaculture. In this study the immunostimulant and protective potential of orally administered AuNP against V. parahaemolyticus, the causative agent of Acute Hepatopancreatic Necrosis Disease, was determined in shrimp. Synthetized AuNP (18.57 ± 4.37 nm) were moderately dispersed with a negative ζ potential of -10.3 ± 0.208 mV (pH = 7). AuNP were administered (single dose) at 0.2, 2, and 20 μg/g feed in shrimp. Hemolymph samples were withdrawn daily for 6 days. Hemolymph or hemocytes were used to determine total hemocyte counts, immune-related enzymatic activities, and expression of immune-relevant genes. Hepatopancreas was sampled for the analysis of AuNP biodistribution and histological examination. Survival was recorded daily. No mortality or toxicity signs in hepatopancreas were found. AuNP were detected in hepatopancreas. Early (24-48 h) immunostimulation was mainly related to immune gene up-regulation. Upon a challenge with V. parahaemolyticus, survival was higher (80%) and histopathological damages were lower in shrimp treated with the 2 μg/g dose when compared to the control. Therefore orally administered AuNP are proposed as immunostimulants that protect shrimp against V. parahaemolyticus infection.

Expression of Macrobrachium rosenbergii lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) in Saccharomyces cerevisiae and evaluation of its immune function

Pattern recognition proteins (PRPs) activate the innate immune system in invertebrates, and lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) is an important PRP with various biological functions. Here, the open reading frame (ORF) of Macrobrachium rosenbergii LGBP (MrLGBP) was cloned into plasmid vector pHAC181, then integrated into downstream of the GAL1 promoter of Saccharomyces cerevisiae strain GAL1-ScRCH1 via homologous recombination, followed by its expression in the yeast eukaryotic system. The resulting recombinant LGBP contained a 3 × HA-tag at its C terminus and had a molecular weight of about 45 kDa, as evaluated by western blot analysis. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were ranged from 0.340 to 0.802 and 1.189-1.810 μM, respectively. The recombinant MrLGBP protein agglutinated almost all tested bacteria except Bacillus thuringiensis and Staphylococcus aureus. These results revealed that this recombinant protein exhibited antimicrobial activity against some Gram-positive and Gram-negative bacteria. M. rosenbergii prawns were fed with the recombinant yeast strain MrLGBP for 1 month and challenged with the most common crustacean pathogen, Vibrio parahaemolyticus. These prawns showed lower mortality and higher enzymatic activity and expression levels of immunity genes than did the control groups. All these results suggest that MrLGBP may play important roles in the innate immunity of crustaceans, and recombinant strain S. cerevisiae MrLGBP may be useful for the development of an effective immune feed additive in the future.

Replacement of fishmeal by spirulina Arthrospira platensis affects growth, immune related-gene expression in gibel carp (Carassius auratus gibelio var. CAS III), and its challenge against Aeromonas hydrophila infection

The present study examined the effect of dietary spirulina, Arthrospira platensis on growth performance, blood physiological indices, immune-related gene expressions and resistance of juvenile gibel carp against Aeromonas hydrophila infection. Four isonitrogenous (360 g kg^-1) and isolipidic (90 g kg^-1) diets were formulated with containing different levels of spirulina powder of 0 g (SP0, the control diet), 3.38 g (SP3.38), 6.76 g (SP6.76) and 13.52 g (SP13.52) per 100 g diet to replace 0%, 25%, 50% and 100% of fishmeal protein, respectively. And each diet was randomly assigned to triplicate tanks (150-L capacity per each) and each tank was stocked with 22 fish (15.37 ± 0.06 g). Fish were fed one of the tested diets up to satiation twice a day for 46 days. A challenge test was carried out after the feeding trial by injecting Aeromonas hydrophila intraperitoneally for 7 days. The results showed that fish growth, feeding rate in groups SP3.38 and SP6.76 were significantly higher than those of groups SP0 and SP13.52 (P < 0.05). Feed efficiency and protein retention rate had no significant difference among all tested groups. Plasma superoxide dismutase and phagocyte activity of blood leukocytes significantly increased in the spirulina-fed fish groups at 12-h post the bacterial challenge (P < 0.05). Both pre and post challenge test, plasma lysozyme activities in spirulina-fed groups were significantly higher than that in the control group (P < 0.05). Plasma malondialdehyde got the lowest value in the SP13.52 group before and after the challenge test. The transcriptional levels of TLR2 (Toll like receptor 2), myeloid differentiation factor 88 (MyD88), Toll/IL-1 receptor domain-containing adaptor protein (TIRAP), interleukin-1β (IL-1β) and tumor necrosis factor-α1 (TNF-α1) in spleen and kidney significantly increased post the bacterial challenge compared to the pre challenge. And the relative expressions of the immune-related genes of spirulina-fed fish groups were higher than those of the control group before and after the challenge test. The 7-day cumulative survival rate after the bacterial challenge was highest in the SP3.38 group (P < 0.05). The present results indicated that low dietary inclusion of spirulina significantly enhanced the immune response of gibel carp partly through TLR2 pathway and 3.38% of dietary spirulina was recommended for the juveniles based on the growth and immune response.

The effect of intermittent hypoxia under different temperature on the immunomodulation in Streptococcus agalactiae vaccinated Nile tilapia (Oreochromis niloticus)

Dissolved oxygen (DO) and temperature are the potential immunomodulators in fish and play the important roles in regulating immunity. We studied the effect of intermittent hypoxia under different temperature on the immunomodulation in vaccinated Nile tilapia (Oreochromis niloticus). The expression of immune-related genes, enzymatic activities, histology, cumulative mortality, and S. agalactiae clearance were assessed. Study conditions were intermittently hypoxic (4.0 ± 1.0 mg/L DO) at 30 ± 0.5 °C or 35 ± 0.5 °C. Interleukin-1beta (IL-1β), tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ) mRNA expression in spleen and head kidney were significantly lower in vaccinated hypoxic fish compared to the vaccinated normoxic fish. Levels of heat shock protein 70 (HSP70) in tissues showed an opposite tendency. Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities were significantly lower in vaccinated hypoxic fish. Malondialdehyde levels were significantly greater under hypoxic conditions. In vitro studies evaluated the effects of intermittent hypoxia at different temperatures on cells of vaccinated O. niloticus. Phagocytic activity of peripheral blood leucocytes (PBLs) and intracellular reactive oxygen species (ROS) production in head kidney cells were significantly decreased by intermittent hypoxia at either 30 °C or 35 °C, while nitric oxide levels in tissues cells increased significantly under hypoxic conditions. These changes were well reflected by the further suppression modulation on S. agalactiae clearance in vaccinated O. niloticus and higher cumulative mortality by intermittent hypoxia. Taken together, intermittent hypoxia at either 30 °C or 35 °C could suppress immunomodulation in vaccinated Nile tilapia.