Effect of microplastics on oxytetracycline trophic transfer: Immune, gut microbiota and antibiotic resistance gene responses

Microplastics and antibiotics are prevalent and emerging pollutants in aquatic ecosystems, but their interactions in aquatic food chains remain largely unexplored. This study investigated the impact of polypropylene microplastics (PP-MPs) on oxytetracycline (OTC) trophic transfer from the shrimp (Neocaridina denticulate) to crucian carp (Carassius auratus) by metagenomic sequencing. The carrier effects of PP-MPs promoted OTC bioaccumulation and trophic transfer, which exacerbated enterocyte vacuolation and hepatocyte eosinophilic necrosis. PP-MPs enhanced the inhibitory effect of OTC on intestinal lysozyme activities and complement C3 levels in shrimp and fish, and hepatic immunoglobulin M levels in fish (p < 0.05). Co-exposure of MPs and OTC markedly increased the abundance of Actinobacteria in shrimp and Firmicutes in fish, which caused disturbances in carbohydrate, amino acid, and energy metabolism. Moreover, OTC exacerbated the enrichment of antibiotic resistance genes (ARGs) in aquatic animals, and PP-MPs significantly increased the diversity and abundance of ARGs and facilitated the trophic transfer of teta and tetm. Our findings disclosed the impacts of PP-MPs on the mechanism of antibiotic toxicity in aquatic food chains and emphasized the importance of gut microbiota for ARGs trophic transfer, which contributed to a deeper understanding of potential risks posed by complex pollutants on aquatic ecosystems.

Transcriptomic analysis of gills in nitrite-tolerant and -sensitive families of Litopenaeus vannamei

Nitrite stress is a major environmental factor that limits aquatic animal growth, reproduction and survival. Even so, some shrimps still can withstand somewhat high concentrations of nitrite environment. However, few studies have been conducted about the tolerance molecular mechanism of Litopenaeus vannamei in the high concentration nitrite. To identify the genes and pathways involved in the regulation of nitrite tolerance, we performed comparative transcriptomic analysis in the L. vannamei nitrite-tolerant (NT) and nitrite-sensitive (NS) families, and untreated shrimps were used as the control group. After 24 h of nitrite exposure (NaNO₂, 112.5 mg/L), a total of 1521 and 868 differentially expressed genes (DEGs) were obtained from NT compared with NS and control group, respectively. Functional enrichment analysis revealed that most of these DEGs were involved in immune defense, energy metabolism processes and endoplasmic reticulum (ER) stress. During nitrite stress, energy metabolism in NT was significantly enhanced by activating the related genes expression of oxidative phosphorylation (OXPHOS) pathway and tricarboxylic acid (TCA) cycle. Meanwhile, some DEGs involved in innate immunity- related genes and pathways, and ER stress responses also were highly expressed in NT. Therefore, we speculate that accelerated energy metabolism, higher expression of immunity and ER related genes might be the important adaptive strategies for NT in relative to NS under nitrite stress. These results will provide new insights on the potential tolerant molecular mechanisms and the breeding of new varieties of nitrite tolerant L. vannamei.

Natural ingredient paeoniflorin could be a lead compound against white spot syndrome virus infection in Litopenaeus vannamei

White spot syndrome virus (WSSV) is an important pathogen causing high mortality in the shrimp industry in aquaculture, yet there is no treatment available to date. In order to find a treatment against WSSV infection, this study examined the anti-WSSV activity of eight natural compounds using shrimp larvae as a model. Among the eight compounds, paeoniflorin showed the most obvious anti-WSSV effect, with a maximum protection efficiency of WSSV-infected shrimp >60% at 100 μM. Furthermore, pretreatment and post-treatment experiments revealed that paeoniflorin could prevent and treat WSSV infection in shrimp. The antiviral activity of paeoniflorin in aquaculture water decreased rapidly with time, and the results showed that the stable anti-WSSV activity of paeoniflorin could only remain in water for 1 day. Thus, the dosing pattern of continuous medication changes was evaluated. Obviously, in the model of continuous change of paeoniflorin, WSSV copy numbers in the virus-treated shrimp group still progressively increased, while the virus content in WSSV_paeoniflorin -treated group continued to decrease. Interestingly, paeoniflorin inhibited horizontal transmission of WSSV to a certain extent. Notably, paeoniflorin significantly increased the expression of antimicrobial peptides of shrimp to resist WSSV. In conclusion, paeoniflorin has the potential to protect shrimp against WSSV.

Assessment of acetylcholinesterase, catalase, and glutathione S-transferase as biomarkers for imidacloprid exposure in penaeid shrimp

Shrimp aquaculture is a valuable source of quality seafood that can be impacted by exposure to insecticides, such as imidacloprid. Here, adult black tiger shrimp (Penaeus monodon) were used to evaluate the activity of acetylcholinesterase (AChE), catalase (CAT), and glutathione S-transferase (GST) in abdominal, head, gill, and hepatopancreas tissue as biomarkers for imidacloprid exposure. Adult P. monodon were continuously exposed to imidacloprid in water (5 μgL^-1 and 30 μgL^-1) or feed (12.5 μg g^-1 and 75 μg g^-1) for either 4 or 21 days. The imidacloprid concentration in shrimp tissues was determined using liquid chromatography-mass spectrometry after QuEChER extraction, and AChE, CAT, and GST activities were estimated by spectrophotometric assay. Imidacloprid exposure in shrimp elevated the activity of biomarkers, and the enzymatic activity was positively correlated to tissue imidacloprid accumulation, although the effects varied in a tissue-, dose- and time-dependent manner. AChE activity was correlated to imidacloprid concentration in the abdominal tissue of shrimp and was likely related to neural tissue distribution, while the activity of CAT and GST confirmed a generalised anti-oxidant stress response. AChE, CAT, and GST were valuable biomarkers for assessing shrimp response to imidacloprid exposure from dietary or water sources, and the abdominal tissue was the most reliable for exposure assessment. An elevated response in each of these biomarkers during routine monitoring could provide an early warning of shrimp stress, suggesting that investigating potential contamination by neonicotinoid pesticides would be worthwhile.

Curcumin-mediated sono/photodynamic treatment preserved the quality of shrimp surimi and influenced its microbial community changes during refrigerated storage

Shrimp surimi is widely acknowledged as a value-added shrimp product due to its delicious taste, rich flavor, and nutrition. However, the refrigerated shrimp surimi is prone to deterioration due to rapid microbial growth during storage. The present study sought to assess the effects of curcumin-mediated sono/photodynamic treatment on bacterial spoilage and shrimp surimi quality stored at 4 °C. The total viable count (TVC), microbiota composition, and quality parameters, including the total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substance (TBARs), and pH were investigated. The results showed that the spoilage bacteria in shrimp surimi rapidly increased with a surge on day 2 during refrigeration storage. The Psychrobacter and Brochothrix were identified as the Specific Spoilage Organisms (SSOs), which were also positively correlated with TVB-N and TBARs. The results further elucidated that the sono/photodynamic treatment could significantly inhibit the growth of SSOs on the surface and interior of shrimp surimi and delay shrimp surimi quality deterioration. In conclusion, the sono/photodynamic treatment as a non-thermal sterilization method could be a reliable and potential method for inactivating spoilage microorganisms and preserving shrimp surimi quality.

Effects of isoquinoline alkaloids from Macleaya cordata on growth performance, survival, immune response, and resistance to Vibrio parahaemolyticus infection of Pacific white shrimp (Litopenaeus vannamei)

Isoquinoline alkaloids (IQs) from Macleaya cordata are promising natural products for enhancing the growth performance and overall health condition of farmed animals. The present study aimed to investigate the effects of two formulas of IQ extract, provided in either a powdered formula (IQ-E) or a water-soluble, granulated formula (IQ-WS) and containing the main active component sanguinarine at a concentration of 0.5% and 1%, respectively, on the growth, survival, immune response, and resistance to Vibrio parahaemolyticus infection of Pacific white shrimp (Litopenaeus vannamei). In Experiment 1, the postlarvae were divided into five groups (four replicates/group and 100 shrimp/tank) and fed four times/day for 30 days with a control feed, IQ-E at 200 or 300 mg/kg of feed, or IQ-WS at 100 or 150 mg/kg of feed. In Experiment 2, the surviving shrimp from Experiment 1 were redistributed into six groups (four treatment groups as in Experiment 1 plus the positive and negative controls with four replicates/group and 30 shrimp/tank) and challenged with V. parahaemolyticus by immersion at a concentration of 103 colony-forming units (CFU)/mL and were fed with the same diets for another 14 days. The results revealed that all IQ-fed shrimp in Experiment 1 had significantly enhanced survival rates and immune parameters (total hemocyte count and phagocytic, phenoloxidase, and superoxide dismutase activities) compared to the control group, even though the growth performances were similar across all groups. In Experiment 2, all IQ-fed groups showed better growth performance and survival rates compared to the positive control. Other than in the positive control group, no histopathological lesions in the hepatopancreas and the intestine were found. In summary, the current study demonstrated the benefits of using IQs from M. cordata as feed additives for improving the growth performance, survival rate, immune responses, and resistance to vibriosis of Pacific white shrimp.

Development of a three-compartment toxicokinetic model for T-2 toxin in shrimp by blindfold particle swarm optimization algorithm

Tricothecenes-2 toxin (T-2) is a major mycotoxin that is widely distributed in aquatic feeds and poses a huge challenge to the aquatic industry, but there is scant information on the toxicokinetics of T-2 in aquatic animals. Here, we describe the development of a three-compartment toxicokinetic model for the absorption, distribution, metabolism and elimination (ADME) of T-2 in shrimp. The three compartments were central (the hemolymph), slow metabolizing and fast metabolizing compartments to account for the varying ADME rates of T-2 in different shrimp organs. The toxicokinetic model was solved by the blindfold particle swarm optimization algorithm, and the values for the model equation parameters were obtained by applying the experimental data of T-2 concentrations in shrimp. The model had a good fit with the experimental data. It was revealed through the model that after i.m. administration, T-2 was rapidly absorbed into the hemolymph and distributed into shrimp organs. The hepatopancreas and intestine belonged to the fast and muscle to the slow metabolizing compartments, respectively, while the hemolymph had no capacity to metabolize T-2. The T-2 elimination rates in the hepatopancreas and intestine were similar and quite high while that in the muscle was very low. The methods used in developing and solving the model could be used for similar toxicokinetic and pharmacokinetic studies of other animals.

Immune toxicity of phenanthrene and its combined effects of white spot syndrome virus on the survival of kuruma shrimp (Penaeus Japonicus)

Shrimp inhabiting coasts that are frequented by humans are exposed to various pollutants. Additionally, viral infections that cause serious damage to shrimp populations have been observed in these environments. The present study sought to evaluate the immunotoxic effects of phenanthrene (Phe), a pollutant detected in coastal environments, on kuruma shrimp (Penaeus japonicus). We further examined the survival of shrimp following combined exposure to Phe (30 or 300 μg/L) and white spot syndrome virus (WSSV). Results show that exposure to Phe for seven days decreased immune system-related parameters, including total hemocyte count and phenoloxidase activity in hemolymph (p < 0.05). However, these effects were not detected after three days of exposure. Moreover, a combined exposure assay revealed that shrimp mortality increased following exposure to 300 μg/L Phe and infection with WSSV. The number of WSSV gene copies was also observed to increase in these co-exposed shrimp. Taken together, these results indicate that long-term Phe exposure impairs the immune system of P. japonicus, resulting in fatal proliferation of WSSV. Hence, considering that combined exposure to Phe and WSSV leads to increased mortality of shrimp, it is imperative that the detrimental effects elicited by multiple stresses be considered, and controlled, in areas inhabited by kuruma shrimp.

The effect of the insecticide diazinon on the osmoregulation and the avoidance response of the white leg shrimp (Penaeus vannamei) is salinity dependent

Diazinon is one of the insecticides that represent a high risk for Costa Rican estuarine environments due to its widespread use in pineapple plantations. In estuaries, organisms are frequently submitted to stress caused by natural factors (e.g., continuous changes in salinity levels) and, additionally, to stress due to contamination. Therefore, the driving question of this study was: will organisms be more susceptible to suffer the deleterious effects caused by diazinon because of the stress resulting from the salinity changes? The estuarine shrimp Penaeus vannamei was used as the model organism and two responses were measured: osmoregulation (the physiological effect after a forced and continuous 24 h-exposure) and avoidance [the behavioural effect after a short (3 h) non-forced, multi-compartmented exposure]. Juveniles were exposed to diazinon (0.1, 1, 10 and 100 μg/L) at three different salinities (10, 20 and 30). Disruption in the capacity to regulate the haemolymph osmotic pressure was observed at a salinity of 30 in individuals exposed to diazinon and methanol (used as vehicle). At that salinity, the ability of shrimps to detect and avoid the highest diazinon concentrations was impaired. P. vannamei juveniles inhabit environments with a high variation in salinity, but with an optimum osmotic point close to a salinity of 20; therefore, the higher the salinity, the greater the vulnerability of shrimps to the effects of diazinon. From an ecological point of view, this combined effect of salinity and contamination might also limit the spatial distribution of the organisms.

In vitro and in vivo immunologic potentiation of herb extracts on shrimp (Litopenaeus vannamei)

In vitro and in vivo effects of Astragalus polysaccharide (APS), chlorogenic acid (CGA) and berberine (BBR) on shrimp (Litopenaeus vannamei) were studied. In vitro test showed that the combination of APS and BBR and the combination of APS and CGA have strong immune enhancement effects and no lysosomal membrane damage on hemocyte. Then, feeding experiment was proceeded to optimize the concentrations of compound herbal extracts. Four diets containing G1-G4(0.5 g kg ^-1 APS + 0.5 g kg ^-1 BBR, 1.0 g kg ^-1 APS +1.0 g kg ^-1 BBR, 0.5 g kg ^-1 APS +0.5 g kg ^-1 CGA, 1.0 g kg ^-1 APS + 1.0 g kg ^-1 CGA) associated with the control group (common diet) were compared and determined their biomolecule damage to hepatopancreas including DNA damage, lipid peroxidation and protein carbonyl. The results indicated that G3 (0.5 g kg ^-1 APS +0.5 g kg ^-1 CGA) showed higher total hemocyte counts, phagocytic activities, antibacterial activities and bacteriolytic activities during 6 days feeding, and without biomolecule damages after 6 days post-withdrawal. Therefore, the appropriate immunostimulants formula in this study was the combination of 0.5 g kg ^-1 APS and 0.5 g kg^-1 CGA, which was used for 6 days followed by 6 days post-withdrawal. Additionally, our study provides new support for screening composite immunostimulants formula by using primary shrimp hemocyte culture.

Effects of Phyllanthus amarus extract on nonspecific immune responses, growth, and resistance to Vibrio alginolyticus in white shrimp Litopenaeus vannamei

This study investigates the effects of Phyllanthus amarus extract (PAE) on immune responses, growth, and resistance to Vibrio alginolyticus in white shrimp (Litopenaeus vannamei). In vitro PAE treatment did not alter the cell viability of haemocytes and significantly enhanced immune parameters such as phenoloxidase (PO) activity, phagocytic activity, and superoxide anion (O₂^-) production. We conducted two feeding trials to examine the effects of PAE on the growth, disease resistance, and innate immune parameters of white shrimp. In the first in vivo trial, shrimps (4.01 ± 0.03 g) were fed a diet containing 0 g (control), 10 g (PAE10), 20 g (PAE20), or 40 g (PAE40) of PAE per kilogram of feed for 56 days. After the feeding period, the PAE20 group showed a significantly higher weight gain and specific growth rate than shrimp fed the control diet. Furthermore, after challenge with V. alginolyticus, shrimp fed a diet containing PAE showed significantly higher survival than those fed the control diet. The second in vivo trial (28 days) was performed to identify the mechanisms of enhanced immunity in PAE-fed shrimp. Shrimp fed the PAE20 diet generally had the highest total haemocyte count, PO activity, phagocytic activity, and O₂^- production, followed by the PAE40 and PAE10 groups. Thus, our results suggest that administration of 20 g of PAE per kilogram of feed can enhance immunity, growth, and resistance to V. alginolyticus in white shrimp.

Physiological changes in the hemolymph of juvenile shrimp Litopenaeus vannamei to sublethal nitrite and nitrate stress in low-salinity waters

Juveniles of the shrimp Litopenaeus vannamei (3.3 ± 0.4 g) were exposed separately to nitrite (0.0, 1.1, 2.6, and 5.3 mg/L nitrogen as nitrite [NO₂^--N]) and nitrate (0, 90, 225 and 400 mg/L nitrogen as nitrate [NO₃^--N]) concentrations equivalent to 0, 10, 25, and 50% of the LC₅₀-96 h value of NO₂^--N and NO₃^--N in low salinity water (3 g/L). Shrimps responded to nitrite and nitrate according to changes in oxyhemocyanin, glucose, lactate and ion levels in the hemolymph after 6, 12, 24, and 48 h of exposure. Oxyhemocyanin levels decreased with increasing nitrite and nitrate levels and were higher at 50% exposure to the contaminants. Compared to the control, glucose and lactate increased significantly at 50% exposure to nitrite and nitrate, particularly at 12 and 24 h. Na⁺ in the hemolymph changed with nitrite and nitrate, while K⁺ only changed ˜with nitrite.

Transcriptome analysis of Penaeus vannamei hepatopancreas reveals differences in toxicity mechanisms between phoxim and prometryne

Due to overuse and terrestrial input, there are large quantities of phoxim and prometryne residues in some aquatic environments. In the present study, the effects of these compounds on Penaeus vannamei hepatopancreas were analysed at the transcriptome level to investigate toxicity in this nontarget aquaculture organism. Twelve normalised cDNA libraries were constructed using RNA from phoxim and prometryne treatment groups, and an untreated control group. A total of 667,750,902 clean reads were obtained. Analysis of differentially expressed genes (DEGs) identified 449 in control vs phoxim groups, 185 in control vs prometryne groups, and 183 in prometryne vs phoxim groups. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, arachidonic acid metabolism, pancreatic secretion, linoleic acid metabolism, and beta-alanine metabolism pathways were significantly enriched in control vs phoxim groups. In control vs prometryne groups, lysosome, pentose and glucuronate interconversion, antigen processing and presentation, and glycosaminoglycan degradation pathways were significantly enriched. In prometryne vs phoxim groups, protein digestion and absorption, extracellular matrix (ECM)-receptor interaction, PI3K-Akt signalling, cell adhesion molecule (CAM), AGE-RAGE signalling related to diabetic complications, focal adhesion, and renin secretion pathways were significantly enriched. In further detailed analysis, glutathione S-transferase (GST), glutathione peroxidase and basic phospholipase A2 were downregulated in the phoxim treatment group, indicating that phoxim damaged hepatopancreas. Upregulation of phospholipase A2 (secretory phospholipase A2-like) indicates possible inflammatory pathological injury to hepatopancreas caused by phoxim. Meanwhile, downregulation of CD63 indicates that prometryne affect the immune system.

Improvement of growth, intestinal short-chain fatty acids, non-specific immunity and ammonia resistance in Pacific white shrimp (Litopenaeus vannamei) fed dietary water-soluble chitosan and mixed probiotics

This study was to explore the impacts of water-soluble chitosan and mixed probiotics on growth performance, intestinal short-chain fatty acids (SCFAs) and immunity and ammonia resistance in Litopenaeus vannamei. Shrimp were fed one of four experimental diets including basal diet (CON), 0.10% water-soluble chitosan diet (WSC), 0.30% mixed probiotics (MP) and 0.10% water-soluble chitosan +0.30% mixed probiotics (SYN) for 8 weeks. Results showed shrimp fed with dietary MP and SYN diets could significantly improve growth performance and feed utilization in comparison with those of shrimp fed with CON diet (P < 0.05). Acetic acid content was significantly higher in shrimp fed with all supplemented diets compared to that in shrimp fed with CON diet (P < 0.05). Compared to shrimp fed with CON diet, dietary WSC and MP significantly influenced the contents and/or activities of aspartate aminotransferase (AST), total protein (TP), superoxide dismutase (SOD), lysozyme (LZM) in serum, SOD, malondialdehyde (MDA), acid phosphatase (ACP) in hepatopancreas and SOD and MDA in intestine. In addition, the gene expression levels of prophenoloxidase (proPO), penaiedin 3a (Pen-3a), crustin (Crustin), serine proteinase (SP), GPX and SOD in hepatopancreas, were significantly upregulated compared to those in CON diet at some time points (P < 0.05). Significantly higher survival rate in all supplemented diets were observed after ammonia challenge (P < 0.05). Therefore, the above results indicated dietary WSC and MP or SYN could enhance intestinal SCFAs content, stimulated antioxidant capacity and immune response, and increase the ammonia resistance of Litopenaeus vannamei. Besides, the growth performance was also improved by dietary MP and SYN.

Effect of disinfection with peracetic acid on the microbial community of a seawater aquaculture recirculation system for Pacific white shrimp (Litopenaeus vannamei)

When tropical shrimps are kept in recirculating aquaculture systems (RAS), one of the limiting factors is the maintenance of a sufficient water quality, and therefore, often disinfectants like peracetic acid (PAA) are added to the water either as prophylactic or treatment measure. In this study, PAA in concentrations of 0.1 mg/L, 1 mg/L and 10 mg/L was applied continuously for 56 days to small-scale seawater RAS stocked with Litopenaeus vannamei. Treatment with 0.1 mg/L did not result in a reduction in the total bacterial amount and therefore was not effective. A concentration of 10 mg/L led to significant changes in the chemical water parameters already after 2 days and was therefore not recommendable. A concentration of 1 mg/L led to increased levels of ammonia and nitrite within 2 days and to a significant increase in the bacterial amount in the water, most probably due to an enhanced growth of heterotrophic bacteria. The microflora showed significant fluctuations, and there were indications that the welfare of the shrimps was affected. Using 1 mg PAA/L for prophylactic use is therefore also not recommendable but might be an alternative option for short-term treatment in cases of disease outbreaks.

Injection of an extract of fresh cacao pod husks into Litopenaeus vannamei upregulates immune responses via innate immune signaling pathways

Immunostimulation is a novel method and a promising development in aquaculture. Products derived from plants exhibit various biological activities. In this study, the hot-water extract isolated from fresh cacao (Theobroma cacao) pod husks (CPHs) was administered by injection to evaluate cellular signaling pathways of innate immunity, the immunostimulating potential, disease resistance, and hypothermal tolerance of white shrimp, Litopenaeus vannamei. Results showed significant increases in the total hemocyte count, semigranular cells, granular cells, phenoloxidase activity, and respiratory bursts (RBs) of hemocytes per unit of hemolymph at 1 day, and in phagocytic activity toward and the clearance efficiency of Vibrio alginolyticus at 1-3 days after shrimp were injected with fresh CPH extract at 40 μg shrimp^-1. However, only RBs per hemocyte had significantly decreased at 1 day after the injection. All immune parameters had returned to control levels by 3 days after receiving fresh CPH extract except for RBs, phagocytic activity, and the clearance efficiency, which had returned to control values by 7 days. Furthermore, at 1 day after the injection, the peroxinectin, prophenoloxidase (proPO) II, toll-like receptors (TLR) 3, signal transducer and activator of transcription (STAT), and crustin in shrimp receiving fresh CPH extract at 20 μg shrimp^-1, and the lipopolysaccharide and β-1,3-glucan-binding protein, proPO II, TLR1, and STAT in shrimp receiving fresh CPH extract at 40 μg shrimp^-1 were significantly higher than those of shrimp receiving saline. After injecting fresh CPH extract at 10-40 μg shrimp^-1 and 40 μg shrimp^-1, the mortality of shrimp challenged with V. alginolyticus and exposed to 14 °C for 96 h significantly decreased, respectively. These results suggest that fresh CPH extract can be used as an immunostimulant and a physiological regulator for shrimp through injection administration to enhance immunological and physiological responses, which can elevate the resistance against V. alginolyticus and tolerance against hypothermal stress in L. vannamei.

Impacts of Methyl Farnesoate and 20-Hydroxyecdysone on Larval Mortality and Metamorphosis in the Kuruma Prawn Marsupenaeus japonicus

Physiological functions of juvenile hormone (JH) and molting hormone have been demonstrated in insects. JH, molting hormone and their mimics (insect growth regulators, IGRs) show endocrine-disrupting effects not only on target pest insects but also on other arthropod species such as crustaceans. However, little is known about the endocrine-disrupting effects of IGRs on benthic crustaceans. In this study, laboratory experiments were conducted to investigate effects of representative innate JH in crustaceans (methyl farnesoate, MF) and molting hormone (20-hydroxyecdysone, 20E, active form of ecdysteroid) on larval stages of the kuruma prawn Marsupenaeus japonicus, which is a decapod crustacean living in warm seawater. Larval development of kuruma prawn progresses in the order of nauplius, zoea, mysis, and then post-larvae with molting and metamorphosis, but it is unknown whether both MF and 20E have crucial roles in metamorphosis and molting of this species. Treatments of either MF or 20E on shrimp larvae were attempted at each developmental stage and those effects were validated. In terms of EC50 values between mortality and metamorphosis, there were apparent differences in the transition from nauplius to zoea (MF: 7.67 and 0.12 μM; 20E: 3.84 and 0.06 μM in survival and metamorphic rates, respectively). In contrast, EC50 values in MF and 20E treatments showed high consistency in the transitions between zoea to mysis (EC50 values for survival; MF: 1.25 and 20E: 0.22 μM), and mysis to post-larvae (EC50 values for survival; MF: 0.65 and 20E: 0.46 μM). These data suggest that nauplius has strong resistance against exposure to MF and 20E. Moreover, both chemicals induced high mortality triggered by the disruption of molting associated with metamorphosis. To our knowledge, this is the first experimental evidence that investigates in vivo physiological functions of MF and 20E in the larval stages of kuruma prawn, shedding light on not only ecotoxicological impacts of IGRs released into nature, but also endocrine mechanisms underlying larval development with metamorphosis in benthic decapod crustaceans.

Impact of imidacloprid on the nutritional quality of adult black tiger shrimp (Penaeus monodon)

Neonicotinoid insecticides, including imidacloprid, are increasingly being used to control insect pests in agricultural and urban areas, and are often detected in aquatic environments. The effects of neonicotinoids on non-target insects have been investigated with respect to behavioural, biochemical, physiological and population-level responses, but information of their effects on crustaceans is limited. This study investigated the adverse effects of both acute and chronic exposure to sublethal concentrations of imidacloprid on the nutritional quality of adult Black Tiger Shrimp (Penaeus monodon). Shrimp were continually exposed to imidacloprid in water (5 μg L^-1 and 30 μg L^-1), or through their food (12.5 μg g^-1 and 75 μg g^-1), for the entire exposure period. Imidacloprid concentrations in water and residues in tissues were quantified using liquid chromatography-mass spectrometry after solid-phase extraction and QuEChER extraction respectively. Within 4 days, shrimp accumulated imidacloprid at up to 0.350 μg imidacloprid per g body weight from water and food exposure. Chronic exposure resulted in a significant decrease in body weight and total lipid content. Fatty acid composition in exposed shrimp was modified relative to controls. Overall, these results demonstrate that neonicotinoid exposure could lead to nutritional deficiency, which has implications for the productivity and food quality of shrimp.

Sargassumhorneri extracts stimulate innate immunity, enhance growth performance, and upregulate immune genes in the white shrimp Litopenaeus vannamei

The white shrimp Litopenaeus vannamei is one of the most commercially important aquatic species. However, intensive farming to meet economic demands has been linked to animal stress and subsequent disease outbreaks. In this study, we explore the immunomodulatory effects of Sargassum horneri hot-water extract (SHE) on the immune parameters of L. vannamei. Hemocytes incubated in vitro with 10 mg/ml of SHE showed the highest response in phenoloxidase (PO) activity and reactive oxygen species production. In the in vivo trials, shrimp were fed diets containing 0 (control), 2.5 (SHE 2.5), 5.0 g (SHE 5.0), and 10 g (SHE10.0) of lyophilized SHE per kg feed for four weeks, after which immune parameters were measured. Group SHE10.0 had the highest total hemocyte count, reactive oxygen species production, and phagocytic rate during the 4-week feeding period, followed by groups SHE5.0 and SHE2.5. However, group SHE5.0 showed a better growth performance among all examined groups after four weeks of rearing. Furthermore, gene expression analysis revealed that L. vannamei fed diets containing 0.5% SHE over 28 days showed significant modulation of 11 immune-related genes, including prophenoloxidase I, prophenoloxidase II, peroxinectin, α2macroglobulin, clotting protein, lysozyme, superoxide dismutase, glutathione peroxidase, penaiedin2-4, and crustin. Combined, these results show that SHE is a functional feed additive that can be applied orally to enhance innate immunity and growth performance of white shrimps.

Effect in white shrimp Litopenaeus vannamei of Eleutherine bulbosa (Mill.) Urb. Powder on immune genes expression and resistance against Vibrio parahaemolyticus infection

This study investigated the influence of Eleutherine bulbosa (Mill.) Urb. on the immune responses, bacterial population in the intestines, and resistance of white shrimp, Litopenaeus vannamei, against infection with Vibrio parahaemolyticus. Shrimp were fed with three dosages of powder, at 6.25 g kg-1 (P6.25), 12.5 g kg-1 (P12.5), and 25 g kg-1 (P25). One dosage of the crude extract was provided, 1.25 g kg-1 (E1.25), and the controls without administration of E. bulbosa consisted of a positive control (PC) and a negative control (NC). Feed supplementation was carried out for 30 days; then shrimp from all treatments were challenged by intramuscular injection with V. parahaemolyticus (10⁶ cfu/mL), except for the NC. The results showed that supplementation with the powder and extract of E. bulbosa for 30 days resulted in significantly higher (P < 0.05) immune responses (total hemocyte count (THC), phenoloxidase activity (PO), respiratory bursts (RBs)), gene expression (prophenoloxidase (proPO), lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP)), and total bacterial count (TBC) compared to PC/NC. In post challenge testing, there were significantly higher levels for THC, PO, RBs, proPO, LGBP, and PE (peroxinetin), and the treatments were able to suppress V. parahaemolyticus in the intestines, hepatopancreas, and muscles and to reduce damage to the muscles and hepatopancreas. The survival rate with P12.5 was significantly higher compared to the other treatments. It was concluded that the shrimp receiving supplementation with the powder and extract of E. bulbosa had increased immunity and resistance against V. parahaemolyticus infection, with the best dosage being the P12.5 treatment.

Toxic effect of chronic waterborne copper exposure on growth, immunity, anti-oxidative capacity and gut microbiota of Pacific white shrimp Litopenaeus vannamei

Copper can be accumulated in water through excessive sewage discharge or residual algaecide to generate toxic effect to aquatic animals. In this study, the juvenile of Pacific white shrimp, Litopenaeus vannamei was exposed to 0 (control), 0.05, 0.1, 0.2, 0.5 or 1 mg Cu²⁺ L^-1 for 30 days. Growth, immune function, anti-oxidative status and gut microbiota were evaluated. Weight gain and specific growth rate of L. vannamei were significantly decreased with the increase of ambient Cu²⁺. Enlarged lumen and ruptured cells were found in the hepatopancreas of shrimp in the 0.5 or 1 mg Cu²⁺ L^-1 treatment. Total hemocyte counts of shrimp in 0.5 or 1 mg Cu²⁺ L^-1 were significantly lower than in the control. The hemocyanin concentration was also significantly increased in 0.2 or 0.5 mg Cu²⁺ L^-1. Lysozyme contents were reduced in shrimp when Cu²⁺ exceeded 0.2 mg L^-1. Meanwhile, activities of superoxide dismutase and glutathione peroxidase were increased in the hepatopancreas and the activity of Na⁺-K⁺ ATPase was decreased in the gills with increasing Cu²⁺. The mRNA expressions of immune deficiency, toll-like receptor and caspase-3 were all significantly higher in the hepatopancreas in 0.05 mg Cu²⁺ L^-1 than in the control. For the diversity of intestinal microbes, Bacteroidetes significantly decreased in 1 mg Cu²⁺ L^-1 at the phylum level. KEGG pathway analysis demonstrates that 1 mg L^-1 Cu²⁺ can significantly alter metabolism, cellular processes and environmental information processing. This study indicates that the concentration of 1 mg L^-1 Cu can negatively impact growth, hemolymph immunity, anti-oxidative capacity and gut microbiota composition of L. vannamei.

Growth and health status of Pacific white shrimp, Litopenaeus vannamei, exposed to chronic water born cobalt

Cobalt (Co) is an important component of vitamin B₁₂, but is toxic to aquatic animals at a high level. In this study, the Pacific white shrimp, Litopenaeus vannamei were exposed to three Co concentrations (0, 100, and 1000 μg/L) for 4 weeks. The survival and condition factor in shrimp exposed to the Co treatments were not different from the control, but the shrimp exposed to 100 μg Co/L gained more weight than in other two groups, and the shrimp exposed to 1000 μg Co/L gained less weight than in other groups. The SOD and GSH-PX activities were higher in shrimp exposed to 100 μg Co/L, but lower in the shrimp exposed to 100 μg Co/L compared with the control, respectively. The MDA contents in the hepatopancreas decreased in the 100 μg Co/L, but increased in the 1000 μg Co/L. The serum lysozyme decreased with ambient cobalt, was lower in the shrimp exposed to 1000 μg Co/L than in other two groups. The expression of C-type lectin 3 was down-regulated by Co concentrations. The Toll and immune deficiency in shrimp exposed to 100 μg Co/L was higher than in other two groups. The mucin-1 was lower in the 1000 μg Co/L group than in other two groups, but mucin-2 and mucin-5AC were higher in the 1000 μg Co/L group than in the control. With increasing Co concentration, Shannon and Simpson indexes of the intestinal microbial communities were decreased. The abundance of pathogenic bacteria (Ruegeria and Vibrio) increased in both Co groups. This study indicates that chronic exposure to waterborne cobalt could affect growth, cause oxidative stress, stimulate the immune response, damage intestinal histology, and reshape intestinal microbiota community L. vannamei.

Effects of chlorpyrifos on the crustacean Litopenaeus vannamei

Shrimps can be used as indicators of the quality of aquatic systems exposed to a variety of pollutants. Chlorpyrifos is one of the most common pesticides found in environmental samples. In order to evaluate the effects of chlorpyrifos, adult organisms of Litopenaeus vannamei were exposed to two sublethal concentrations of the pesticide (0.7 and 1.3 μg/L) for four days. The LC₅₀ (96-hours) value was determined and Lipid oxidation levels (LPO) and the activities of catalase (CAT), glutathion peroxidase (GPx), glutathion-S-transferase (GST) were assessed on the muscle, hepatopancreas and gills from the exposed organisms. In addition, inhibition of acetylcholinesterase (AChE) was determined in the brain. LC₅₀ (96-hours) was 2.10 μg/L of chlorpyrifos. Catalase activity and LPO were elevated in the three tissues, whereas a decrease of AChE activities in the brain and an increase of GST activity in the hepatopancreas were observed.

Immunological response of white shrimp (Litopenaeus vannamei) to sublethal concentrations of malathion and endosulfan, and their mixture

Cellular and humoral responses were evaluated in Litopenaeus vannamei juveniles when exposed to malathion, endosulfan, and their mixture. Each experiment was performed in the hemolymph collected at each exposure time (5 and 96 h) in duplicate; total hemocyte count, coagulation time, hemocyanin concentration, phenoloxidase (PO) and superoxide dismutase (SOD) activities were quantified. Survival was not affected by pesticides applied individually and mixed. Clotting time did not show significant differences concerning increase of concentration percentage of the pesticides tested. In organisms exposed to the pesticide mixture, hemocyanin decreased at 5 h of exposure as the concentration increased. Only in the malathion experiment did exposed shrimp to 10 and 50% of the LC₅₀-96 h show significantly (p < 0.05) higher hemocyte contents. For malathion, significantly (p < 0.05) lower PO values in shrimp exposed to higher concentrations (10 and 50% of the LC₅₀-96 h) were determined. While for the mixture treatment, high SOD value was determined at high exposure time and concentration. Malathion was the pesticide that showed an effect on some variables even at sublethal concentrations. The Continuous Concentration Criteria of the United States Environmental Protection Agency did not represent effects on the variables when they were compared with the averages of the control group.

Effects of T-2 toxin on the muscle proteins of shrimp (Litopenaeus vannamei) - a proteomics study

BACKGROUND

T-2 toxin (T-2) is a potent mycotoxin and a common contaminant of aquatic animal feed, posing a serious risk to health and aquatic animals. We investigated the effect of T-2 on shrimp muscle proteins using proteomics and conventional biochemical methods. Shrimp were fed a diet containing T-2 at 0-12.2 mg kg^-1 for 20 days, and changes to the muscle protein composition, ATPase activities, and the sulfhydryl (SH) content and hydrophobicity of actomyosin (AM) were determined. A proteomics study of the proteins was conducted with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional (2D) electrophoresis, and matrix-assisted laser desorption/ionization - time of flight mass spectrometry (MALDI-TOF/TOF MS).

RESULTS

Exposure to T-2 markedly affected the muscle protein composition of shrimp in a concentration-responsive manner that displayed a diphasic effect. At a low T-2 concentration (1.2 mg kg^-1 ), the levels of three major muscle proteins (myofibrillar, sarcoplasmic, and stroma) increased but at higher concentrations they declined progressively. T-2 exposure also led to a breakdown of muscle proteins as evidenced by increases in alkali-soluble protein and the surface hydrophobicity (SoANS) of AM. Thirty differentially expressed proteins were detected, 12 of which showed a concentration-response relationship with T-2 exposure. Among them, 11 homologous proteins were identified by mass spectrometry (MS), with several being key enzymes in energy metabolism.

CONCLUSION

This study demonstrated that T-2 exposure at medium to high concentrations could significantly affect the protein composition and quality of shrimp muscle, and potentially some of its key metabolisms. One of the arginine kinases (spot 27) was particularly responsive to T-2 and could potentially be used as a biomarker protein for T-2 intoxication by shrimp. © 2019 Society of Chemical Industry.

Effects of ammonia stress on the hemocytes of the Pacific white shrimp Litopenaeus vannamei

Ammonia is an important environmental stress factor in aquaculture. Long-term ammonia stress could affect the normal growth, and also increase the risk for the occurrence of various diseases. In order to learn the mechanism that ammonia caused the outbreak of the shrimp disease, transcriptomics and metabolomics approaches were used to analyze the differential expressions of the genes in hemocytes and different metabolites in the serum of the Pacific white shrimp Litopenaeus vannamei under ammonia exposure. Transcriptional analysis showed that 17 cell apoptosis related genes, seven phagocytosis related genes, 10 immunity related genes and seven cell cycle and lipid metabolism related genes showed differential expressions after ammonia exposure. Metabolomics analysis on the serum showed that 25 differential metabolites were identified in positive and negative ion patterns. They are involved in purine metabolism, amino acids metabolism and lipid metabolism. Injection of two up-regulated metabolites triethanolamine and oxypurinol to normal shrimp could induce apoptosis in normal shrimp. The total hemocytes counts in shrimp showed a significant decrease and the apoptotic cell ratio increased significantly under ammonia exposure. These results suggested that ammonia exposure increased the apoptosis of hemocytes, which affected the immunity of shrimp, and thus caused susceptibility to pathogenic infection. These data will help us understand the mechanism of ammonia stress leading to the immunity decline of shrimp.

Effects of dopamine on immune signaling pathway factors, phagocytosis and exocytosis in hemocytes of Litopenaeus vannamei

Dopamine (DA) is an important neuroendocrine factor, which can act as neurotransmitter and neurohormone. In this study, we explored the immune defense mechanism in Litopenaeus vannamei with injection of dopamine at 10^-7 and 10^-6 mol shrimp^-1, respectively. The genes expressions of dopamine receptor (DAR), G proteins (Gs, Gi, Gq), phagocytosis and exocytosis-related proteins, as well as intracellular signaling pathway factors, and immune defense parameters were measured. Results showed that mRNA expression levels of dopamine receptor D4 (D4), Gi, nuclear transcription factors and exocytosis-related proteins decreased significantly and reached the minimum at 3 h, while the genes expressions of Gs, Gq and phagocytosis-related proteins reached the highest and lowest levels at 3 h and 6 h, respectively. The second messenger synthetases increased significantly in treatment groups within 3 h. Simultaneously, the second messengers and protein kinases shared a similar trend, which were significantly elevated and reached the peak value at 3 h. Ultimately lead to the total hemocyte count (THC), proPO activity and phagocytic activity decreased significantly, reaching minimum values at 3 h, 3 h and 6 h, respectively. While PO activity showed obvious peak changes, which maximum value reached at 3 h. These results suggested that DA receptor could couple with G protein after DA injection and might regulate immunity through cAMP-PKA, DAG-PKC or CaM pathway.

Responses of hemocyanin and energy metabolism to acute nitrite stress in juveniles of the shrimp Litopenaeus vannamei

Nitrite is a common toxic substance in culture systems of Litopenaeus vannamei, and the stress may disturb hemocyanin synthesis and energy metabolism and result in shrimp death. In the present study, nitrite at concentrations of 0 (control), 3.3 (46.2 NO₂-N mg/L), 6.6 (92.4) and 9.9 mM (138.6) was used to evaluate the responses of hemocyanin level and energy metabolism in L. vannamei (5.80 ± 0.44 cm, 1.88 ± 0.38 g) for 96 h. The mortality rate at 96 h increased with nitrite concentration (50% at 9.9 mM, 40% at 6.6 mM, 30% at 3.3 mM, and 10% at 0 mM). In general, HIF-1α and hemocyanin mRNA expression in the nitrite stress groups was upregulated from 6 to 12 h and downregulated from 24 to 96 h. In the hemolymph, nitrite levels were significantly elevated in a dose-dependent manner, and exposure to nitrite stress significantly decreased the oxyhemocyanin content from 24 to 96 h. The glucose and lactate levels in the hemolymph in the nitrite stress groups were higher than those in the control group from 12 to 96 h. Compared with the control group, the shrimp in the nitrite stress groups exhibited decreased glycogen concentrations in the hepatopancreas. The triglyceride (TG) levels in the nitrite stress groups were all higher than those in the control group from 48 to 96 h. The hexokinase (HK) activity in the hepatopancreas and muscle increased in the nitrite stress groups from 48 to 96 h. In general, nitrite stress enhanced the activities of pyruvate kinase (PK), phosphofructokinase (PFK) and lactate dehydrogenase (LDH) in muscle from 24 to 96 h. In addition, nitrite stress decreased the activities of succinate dehydrogenase (SDH) and fatty acid synthase (FAS) from 24 to 96 h in the hepatopancreas and muscle. This study indicates that exposure to nitrite stress can enhance the accumulation of nitrite in the hemolymph and then reduce oxygenation and hemocyanin synthesis, leading to tissue hypoxia and thereby resulting in accelerated anaerobic metabolism and the inhibition of aerobic metabolism. The effects of nitrite stress on hemocyanin synthesis and energy metabolism may be one of the reasons for the mortality of L. vannamei in culture systems.

Effect of sublethal gradient concentrations of nickel on postlarvae of Penaeus monodon, Perna viridis and Terapon jarbua: Enzyme activities and histopathological changes

The present study evaluates the enzyme activities and histopathological changes in the post larvae (PL) of shrimp (Penaeus monodon), green mussel (Perna viridis) and fingerlings of crescent perch (Terapon jarbua) exposed to sublethal gradient concentrations of Nickel (Ni). The median lethal concentration (LC₅₀) values were 2.49, 66.03 and 43.92 mg Ni L^-1 derived for the PL of shrimp, green mussel and fish fingerlings respectively. No Observed Effect Concentration (NOEC), Lowest Observed Effect Concentration (LOEC) and chronic values of the PL of shrimp were 46.5, 73.0 and 58.3 μg Ni L^-1 derived for the 21-d survival endpoint. The NOEC, LOEC and chronic values for the 30-d survival endpoint of the green mussels and fish fingerlings were 4.6, 6.32, 5.4 and 1.95, 2.6, 2.25 mg Ni L^-1 respectively. The isoforms of esterase, superoxide dismutase and malate dehydrogenase activities in the whole body tissues of test organisms were studied by native polyacrylamide gel electrophoresis after exposure to Ni. Histological examination of compound eye sections of shrimp revealed deformation, compression, fusion and detachement in the corneal cells from the corneal facet of the ommatidia indicating cellular anomalies due to Ni toxicity. Gill sections of the green mussel witnessed reduced haemolymph in sinuses of gill filaments, degenerative changes in interfilamentous junction and necrosis of frontal ciliated epithelial cells with vacuoles after exposure to Ni. Nickel affects the vision of shrimp and fish fingerlings, gills and byssus of green mussels.

Exploration of the influence of surface proteins on the probiotic activity of Lactobacillus pentosus HC-2 in the Litopenaeus vannamei midgut via label-free quantitative proteomic analysis

Our previous work showed that using Lactobacillus pentosus HC-2 as a probiotic could improve the growth performance, immune response, gut bacterial diversity and disease resistance of Litopenaeus vannamei. However, the probiotic mechanism had not been fully characterized. In the present study, histology and proteomic analysis were performed to explore the influence of HC-2 surface protein on its probiotic effects on L. vannamei after feeding either the intact surface proteins, the probiotic treated with lithium chloride (LiCl) to remove noncovalently bound surface proteins or no probiotic for four weeks. Histological observation found that feeding with normal HC-2 obviously improved the intestinal histology and enhanced the protective effect against pathogen damage, but feeding with LiCl-treated HC-2 did not improve the intestinal environment. A total of over 2764 peptides and 1118 uniproteins were identified from the L. vannamei midgut; 211 proteins were significantly differentially expressed in the normal HC-2 group compared with the control group; 510 proteins were significantly differentially expressed in the LiCl-treated HC-2 group compared with the control group, and 458 proteins were significantly differentially expressed in the LiCl-treated HC-2 group compared with the normal HC-2 group. GO/KEGG enrichment analysis of the significantly different proteins demonstrated that feeding normal HC-2 mainly induced immune response, metabolic, cell adhesion and cell-cell signaling-related protein upregulation, which contributed to bacterial adhesion and colonization in the midgut to improve the shrimp immune system and growth, but these proteins were suppressed after the shrimp were fed bacteria deprived of surface proteins. Taken together, these results indicate that the surface proteins were indispensable for HC-2 to execute probiotic effects in the shrimp midgut.

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.

Effect of ammonia stress on immune variables of Pacific white shrimp Penaeus vannamei under varying levels of pH and susceptibility to white spot syndrome virus

Of late, Pacific white shrimp Penaeus vannamei culture has intensified globally and is a major contributor to the cultured shrimp produced worldwide. Intensification of its culture has led to elevated ammonia concentration during grow-out. Ammonia toxicity is a function of water pH, temperature, salinity and beyond the optimum range, creates stress to cultured aquatic species which can reduce growth, increase susceptibility to diseases and eventually mortality. The present study was aimed at quantifying the toxic effect of total ammonia nitrogen (TAN) (1, 3, 6 & 9 mg/l) and pH levels (6, 8 & 10) individually and in combination on median survival (50% lethal time) of shrimp (8 g) after exposure for 14 days followed by post-stress challenge with white spot syndrome virus (WSSV) for 9 days. Mortality risk factor and the toxicity effect on the immune variables were evaluated. Individual stressors showed a risk factor of 1-13 times, whereas combined treatments considerably increased the risk of dying compared to control. Low survival (15%) was observed in pH6TAN9 and pH10TAN3 treatments and was substantiated by prominent histological obliteration in gills of shrimp. The cumulative mortality in post-stress WSSV challenged trials was 1-5 times and 1-35 times in individual and combination treatments, respectively compared to control. The study revealed that variations in ammonia and pH beyond the optimal range significantly influence the non-specific immune mechanisms in P.vannamei and increases the susceptibility to WSSV especially in combination treatments.

Effect of phlorotannins on melanosis and quality changes of Pacific white shrimp (Litopenaeus vannamei) during iced storage

Effect of phlorotannins (PT) treatments on the ployhenoloxidase (PPO) activity and quality changes of Pacific white shrimp during a 16-day period of storage in ice were studied. Among seaweeds, Sargassum tenerimum had the highest amount of PT (10.00 mg phloroglucinol/g), PPO inhibitory activity (71.94%) and therefore selected for PT extraction. The shrimp treated with 5% PT (w/v) showed the least melanosis score, pH, TVB-N values and lipid oxidation among all treatments throughout the iced storage. Lower counts of mesophilic and psychrotrophic bacteria (1-2 log CFU/g) were obtained with 5% PT treatment compared to the control at the last day of storage (P < 0.05). Sensory evaluation proved that 5% PT treatment could cause a 4-days increase in the shelf-life of shrimp compared to the control, PT1% and PT2% treatments. Therefore, 5% phlorotannins from S. tenerimum could be used as a safe melanosis inhibitor for the treatment of shrimp.

Probiotic effects of Bacillus spp. from Pacific white shrimp (Litopenaeus vannamei) on water quality and shrimp growth, immune responses, and resistance to Vibrio parahaemolyticus (AHPND strains)

Acute hepatopancreatic necrosis disease (AHPND), a serious disease caused by some Vibrio spp., impacts the Pacific white shrimp industry worldwide, especially in Thailand. To effectively overcome this problem, efficacious probiotic candidates were isolated from shrimp farms near coastal areas. The isolated Bacillus probiotics were screened for their ability to control pathogenic Vibrio spp. and various V. parahaemolyticus AHPND (VP_AHPND) strains. Among the obtained probiotics, Bacillus subtilis AQAHBS001, which broadly inhibited various strains of VP_AHPND, was evaluated on a laboratory scale in water-soluble and feed applications of viable probiotic. The water addition of 1 × 10³-1 × 10⁵ CFU/mL of this probiotic effectively reduced total ammonia but did not improve shrimp growth and resistance to VP_AHPND. However, feed supplemented with the selected probiotic at 1 × 10⁷ and 1 × 10⁹ CFU/kg diet and provided to shrimp continuously for 5 weeks efficiently improved growth, as indicated by significant final weight gain, average daily growth, specific growth rates and feed conversion ratios. Additionally, this probiotic significantly elevated immune responses through phagocytic activity and clearance efficiency and enhanced the expression of the prophenoloxidase, lysozyme, and anti-lipopolysaccharide factor genes. Furthermore, B. subtilis AQAHBS001 obviously improved midgut characteristics by increasing microvilli and intestinal wall thickness. Finally, this probiotic evidently improved resistance to VP_AHPND.

Bioencapsulation efficacy of sulfated galactans in adult Artemia salina for enhancing immunity in shrimp Litopenaeus vannamei

Live food organisms like Artemia have been used for delivery of different substances such as nutrients, probiotics and immune-stimulants to aquatic animals. Previously, we reported that sulfated galactans (SG) from the red seaweed Gracilaria fisheri (G. fisheri) increased immune activity in shrimp. In the present study we further investigated the capacity and efficiency of bioencapsulation of SG in adult Artemia for delivery to tissues and potentially boosting the expression of immune genes in post larvae shrimp. SG were labelled with FITC (FITC-SG) for in vivo tracking in shrimp. Bioencapsulation of adult Artemia with FITC-SG (0-100 μg mL^-1) was performed and the fluorescence intensity was detected in the gut lumen after enrichment periods of 30 min, 1 h, 2 h, 6 h and 24 h. The results showed the Artemia took up SG over time in a concentration-dependent manner. Shrimp were fed with the bioencapsulated Artemia (FITC-SG, 20 μg mL^-1) and the shrimp were evaluated under a stereo-fluorescent microscope. At 24 h after administration, FITC-SG was located in gills and hepatopancreas and also bound with haemocytes. With daily SG administration, the genes IMD, IKKβ were up-regulated (after 1 day) while genes dicer and proPO-I were up-regulated later (after 7 days). Moreover, continued monitoring of shrimp fed for 3 consecutive days only with SG at the dose of 0.5 mg g^-1 BW showed increases in the expression of IMD, IKKβ genes on day 1 and which gradually declined to normal levels on day 14, while the expression of dicer and proPO-I was increased on day 3 and remained high on day 14. These results demonstrate that bioencapsulation of SG in adult Artemia successfully delivers SG to shrimp tissues, which then bind with haemocytes and subsequently activate immune genes, and potentially increase immunity in shrimp. In addition, the present study suggests that a 3-consecutive-day regimen of SG supplemented in Artemia (0.5 mg g^-1 BW) may boost and sustain the enhanced immune functions in post larvae shrimp.

Neuroendocrine and immunotoxicity of polyaromatic hydrocarbon, chrysene in crustacean post larvae

Polyaromatic hydrocarbons are a group of chemical pollutants which cause a significant threat to the living organisms in estuaries and marine ecosystems. We report the effect of chrysene, a major PAH pollutant found in Cochin Estuary along the southwest coast of India, on the neuroendocrine and immune gene expression of the post larvae (PL-25) of Penaeus monodon. The PL- 25 of P. monodon were administered with feed coated with increasing concentrations of chrysene (1, 2 and 3 µg/g) for 10 days and the gene expression was studied on 7th, 11th and 15th day. The PL exposed to chrysene showed moulting stress and changes in the levels of moult-inhibiting hormone I (MIH I) indicated by irregular moulting in the experimental tanks. At the molecular level, the higher concentration of chrysene induced two-fold upregulation of neuroendocrine (MIH I) and downregulation of immune (ProPO and crustin) gene on the 7th day of exposure. The expression of MIH I gene reduced on withdrawing the experimental feed (on 11th day), while continued downregulation of ProPO and crustin were observed on the 11th day. The results of the present study indicate that the microgram levels of PAH can impinge the neuroendocrine and immune system of the P. monodon, which may induce morbidity and mortality to the larvae in polluted coastal ecosystems. Therefore, more attention may be given to avoid PAH pollution in the estuaries to maintain a healthy ecosystem and to protect the animals from extinction.

Stress response and tolerance mechanisms of ammonia exposure based on transcriptomics and metabolomics in Litopenaeus vannamei

Ammonia, one of the major limiting environment factors in aquaculture, may pose a threat to the shrimp growth, reproduction and survival. In this study, to understand molecular differences of transcriptomic and metabolomic responses and investigate the tolerance mechanisms underlying ammonia stress in Litopenaeus vannamei, ammonia-tolerant family (LV-AT) and ammonia-sensitive family (LV-AS) of these two extreme families were exposed to high-concentration (NH₄Cl, 46 mg/L) ammonia for 24 h. The comparative transcriptome analysis between ammonia-treated and control (LV-C) groups revealed involvement of immune defense, cytoskeleton remodeling, antioxidative system and metabolic pathway in ammonia-stress response of L. vannamei. Likewise, metabolomics analysis showed that ammonia exposure could disturb amino acid metabolism, nucleotide metabolism and lipid metabolism, with metabolism related-genes changed according to RNA-seq analysis. The comparison of metabolite and transcript profiles between LV-AT and LV-AS indicated that LV-AT used the enhanced glycolysis and tricarboxylic acid (TCA) cycle strategies for energy supply and ammonia excretion to adapt high-concentration ammonia. Furthermore, some of genes involved in the detoxification and ammonia excretion were highly expressed in LV-AT. We speculate that the higher ability of ammonia excretion and detoxification and the accelerated energy metabolism for energy supplies might be the adaptive strategies for LV-AT relative to LV-AS after ammonia stress. Collectively, the combination of transcriptomics and metabolomics results will greatly contribute to incrementally understand the stress responses on ammonia exposure to L. vannamei and supply molecular level support for evaluating the environmental effects of ammonia on aquatic organisms. The results further constitute new sights on the potential molecular mechanisms of ammonia adaptive strategies in shrimps at the transcriptomics and metabolomics levels.

Individual and combined effects of ammonia-N and sulfide on the immune function and intestinal microbiota of Pacific white shrimp Litopenaeus vannamei

In this study, we explored the individual and combined effects of ammonia-N and sulfide stress (1 mg/L sulfide and 15 mg/L ammonia-N) on the oxidation resistance, immune response and intestinal health of Litopenaeus vannamei during 72 h exposure. The total antioxidant capacity (T-AOC), malonaldehyde (MDA) and nitric oxide (NO) content, superoxide dismutase (SOD) and catalase activity (CAT), the immune-relative gene (caspase-3, hsp70 and IMD) expression in hepatopancreas and intestine of L.vannamei and the intestinal microbiota were measured. The result showed that MDA and NO contents in hepatopancreas of L. vannamei in all treatment groups increased and remain were at high levels at the end of the stress exposure. The L. vannamei employ antioxidant defense system by increasing the activities of T-AOC, SOD and CAT enzymes in hepatopancereas and intestine to reduce oxidant damage. More severe damages with combined ammonia-N and sulfide stress to antioxidant systems were observed. The gene expression results also demonstrated that antioxidant capacity of L. vannamei was severely impaired and the apoptosis cell was initiated under the ammonia-N and sulfide stress. In addition, the environmental stress also reshaped the intestinal microbial community structure of L. vannamei that a number of original genera decreased, such as Cellvibrio, Vibrio and Rheinheimera; some new genera increased or appeared, such as Photobacterium in all treatment groups, Arcobacter and Fusibacter in sulfide stress group. Therefore, the health of L. vannamei was severely impacted when exposed to the stress of ammonia nitrogen and sulfide and these two factors can have weak synergic effects.

The influence of surface proteins on the probiotic effects of Lactobacillus pentosus HC-2 in the Litopenaeus vannamei hepatopancreas

Our previous work showed that Lactobacillus pentosus HC-2 has high antibacterial and adhesion activity, and as a probiotic could improve the nutrients and immunomodulatory effects in the Litopenaeus vannamei farming. In order to further investigate the influence of HC-2 surface protein on its probiotic effects, the immune and digestion related genes expression and enzymes activities, the colonization numbers of HC-2, and the histologic characteristics were analysis in shrimp hepatopancreas after feeding either the intact surface proteins, the probiotic treated with lithium chloride (LiCl) to remove noncovalently bound surface proteins or no probiotic for four weeks. The results showed that the immune genes expression of lysozyme, proPO, LGBP, Penaeidins-3α, crustin and C-type lectin, the immune enzymes activities of superoxide dismutase, catalase and Alkaline phosphatase, and the digestion enzymes of Trypsin, Lipase and α-Amylase were significantly higher in hepatopancreas of shrimp fed with intact HC-2 than that in shrimp fed with base diet or striped surface proteins HC-2 post feeding and challenge. In addition, the shrimp fed with intact HC-2 leads to the bacteria cells adhesion to hepatopancreas was significantly higher than that in shrimp fed with no surface proteins HC-2. Furthermore, the tissue damages of hepatopancreas caused by pathogenic vibrio were obviously observed in shrimp fed with base diet or no surface proteins HC-2, but no signs of damages were found in shrimp fed with intact HC-2. These results demonstrate that surface proteins are important components for HC-2 to execute probiotic effect that improve hepatopancreas immune response and nutrition digestion to protect shrimp against pathogen damage.

Dietary supplementation with polypeptides improved growth performance, antibacterial immune and intestinal microbiota structure of Litopenaeus vannamei

Antibacterial peptides (AMPs) are expected to replace some or all of the antibiotics and become a new feed additive. However, the high production cost and unclear mechanism limited the application of AMPs. In this research, the effects of a commercial polypeptide (Polypeptide S100) whose main components are AMPs on the growth, antibacterial immune and intestinal microbial of Litopenaeus vannamei were study. L. vannamei (initial weight of 0.16 ± 0.03 g) were fed for 123 days with basal diet added Polypeptide S100 at two levels each (0.5% and 1%) as experimental groups, and a basal diet as control. Dietary inclusion of Polypeptide S100 at 1% level significantly increased the weight gain (WG) and specific growth rate (SGR) of L. vannamei. The survival rates of L. vannamei in 0.5% and 1% Polypeptide S100 groups were significantly higher than the control when infected by Vibrio harveyi but not Vibrio parahaemolyticus. The activities of total superoxide dismutase (T-SOD) and lysozyme (LZM) in the two experimental groups were all significantly higher than the control. Differently, the activities of amylase (AMS) and lipase (LPS) were significantly higher in 0.5% Polypeptide S100 group but lower in 1.0% Polypeptide S100 group. Illumina MiSeq high-throughput sequencing showed that the dominant phyla in the intestine of L. vannamei were Proteobacteria, followed by Actinobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Fusobacteria and Tenericutes, and the abundance of predominant phyla Cyanobacteria were upregulated significantly in the experimental groups. At the family level, significant increase was observed in Pseudomonadaceae and Xanthomonadaceae but decrease in Vibrionaceae in the 1.0% Polypeptide S100 group. The abundance of predominant genus Photobacterium were obviously downregulated in the two experimental groups. Unlikely, the abundance of Pseudomonas and Stenotrophomonas were distinctly increased in the 1.0% Polypeptide S100 group but not significantly different from the control in 0.5% Polypeptide S100 group. All these results suggested that Polypeptide S100 could improve the growth performance, antibacterial immune and intestinal microbiota structure of L. vannamei.

Occurrence of neonicotinoids and fipronil in estuaries and their potential risks to aquatic invertebrates

This study aimed to evaluate and qualify field-based potential risks of seven neonicotinoid and phenylpyrazole (fipronil) insecticides on aquatic invertebrates, including estuary-resident marine crustaceans. One hundred and ninety-three estuarine water samples, with salinity ranging from 0.5 to 32.7, were collected from four estuarine sites in the Seto Inland Sea of Japan, in 2015-2018 and the insecticide levels were measured. Five neonicotinoid and fipronil insecticides were successfully identified, and their occurrence varied temporally. Marine crustaceans were simultaneously harvested every month from one of the estuarine water sampling sites in 2015-2017. Three predominant crustacean species, kuruma prawn (Penaeus japonicus), sand shrimp (Crangon uritai), and mysid (Neomysis awatschensis), were captured and their seasonal presence was species independent. A 96-h laboratory toxicity study with the insecticides using kuruma prawn, sand shrimp, and a surrogate mysid species (Americamysis bahia) indicated that fipronil exerted the highest toxicity to the three crustaceans. Using both toxicity data and insecticide occurrence in estuarine water (salinity ≥10, n = 169), the potential risks on the three marine crustaceans were quantified by calculating the proportion of mixture toxicity effects (P_mix). The P_mix of seven neonicotinoids on the crustaceans was less than 0.8%, which is likely to be too low to indicate adverse effects caused by the insecticides. However, short temporal detection of fipronil (exclusively in June and July) significantly affected the P_mix, which presented the maximal P_mix values of 21%, 3.4%, and 72% for kuruma prawn, sand shrimp, and mysid, respectively, indicating a significant effect on the organisms. As for estuarine water (salinity <10), some water samples contained imidacloprid and fipronil exceeding the freshwater benchmarks for aquatic invertebrates. The present study provides novel insights into the seasonally varying risks of insecticides to estuarine crustaceans and highlights the importance of considering whether ecological risk periods coincide with crustacean presence.

Buton Forest Onion Extract (<i>Eleutherine bulbosa</i> (Mill.) Potential on Growth Performance of Vannamei Shrimp (<i>Litopenaeus vannamei</i>)

BACKGROUND AND OBJECTIVE

Vannamei shrimp Litopenaeus vannamei is an economically valuable aquaculture commodity but still faces problems due to disease and growth performance. Buton forest onion extract Eleutherine bulbosa (Mill.) Urbhas been shown can protect the shrimp from disease. This study aimed to evaluate the potential of the Buton forest onion extract on the growth of vannamei shrimp in tarpaulin pond.

MATERIALS AND METHODS

The experiments were conducted for 90 days by adding Buton forest onion extract in feed at a dosage of 40 g kg-1. The Buton forest onion bulbs was extracted by maceration method using 96% ethanol. The test feed was made through the re-pelleting method. Treatment include supplementation of Buton forest onion extract diet supplemented with Buton forest onion extract diet at twice a week (treatment A) and control was without Buton forest onion extract(treatment K). Parameter measurement include final weight, average daily growth (ADG), feed conversion ratio (FCR), survival rate and water quality (temperature, salinity, turbidity and pH).

RESULTS

This study was demonstrated the addition of Buton forest onion extract on feed with a frequency twice a week in significantly improve the growth performance of vannamei shrimp by improving the final weight and average daily growth at 65 and 90 days of maintenance. Water quality during the study was still within the optimum range for L. vannamei shrimp growth.

CONCLUSION

This study showed that supplementation of Buton forest onion extract was able to improve the growth performance of shrimp in tarpaulin ponds.

Toxicity of ammonia, nitrite and nitrate to Litopenaeus vannamei juveniles in low-salinity water in single and ternary exposure experiments and their environmental implications

Information on toxicity of nitrogen compounds for Litopenaeus vannamei in coastal ecosystems and culture under low salinity is scarce. Acute toxicity trials were conducted in L. vannamei to determine the single and combined effects of ammonia, nitrite and nitrate at a salinity of 3 g/L. The 96 h-LC₅₀ was 29.0 mg/L for total ammonia nitrogen (TAN); 10.6 mg/L for nitrogen as nitrite (NO₂^--N); and 900 mg/L for nitrogen as nitrate (NO₃^--N). The joint effects of ammonia, nitrite and nitrate exposure were antagonistic at 24-72 h; and additive from 72 to 96 h. The proposed safety levels of single exposure to TAN, NO₂^--N and NO₃^--N for L. vannamei are 1.45, 0.53 and 45.0 mg/L, respectively. When in mixture, the proposed level of TAN/NO₂^--N/NO₃^--N is 0.05 TU (Toxicity Unit) corresponding to 0.48, 0.08 and 14.6 mg/L of TAN, NO₂^--N and NO₃^--N, respectively.

Anti-PirA-like toxin immunoglobulin (IgY) in feeds passively immunizes shrimp against acute hepatopancreatic necrosis disease

Acute hepatopancreatic necrosis disease (AHPND), caused by a toxin-producing Vibrio parahaemolyticus strain, has become a serious threat to shrimp aquaculture. The need to regulate antibiotic use prompted the development of alternative ways to treat infections in aquaculture including the use of chicken egg yolk immunoglobulin (IgY) for passive immunization. This study evaluated the protective effect of IgY against AHPND infection in Litopenaeus vannamei (Boone). IgY was isolated from eggs laid by hens immunized with recombinant PirA-like (rPirA) and PirB-like (rPirB) toxins. Whole-egg powders having IgY specific to rPirA (anti-PirA-IgY) and rPirB (anti-PirB-IgY) and IgY from non-immunized hen (control-IgY) were mixed with basal diets at 20% concentrations and used to prefeed shrimp 3 days before the bacterial challenge test. Survival rates of the challenged shrimp fed the anti-PirA-IgY, anti-PirB-IgY and control-IgY diets were 86%, 14% and 0%, respectively. Only the feed containing anti-PirA-IgY protected shrimp against AHPND. Increasing the concentration of rPirA antigen to immunize hens and lowering the amount of egg powder in feeds to 10% consistently showed higher survival rates in shrimp fed with anti-PirA-IgY (87%) compared with the control (12%). These results confirm that addition of anti-PirA-IgY in feeds could be an effective prophylactic method against AHPND infection in shrimp.

Effect of organophosphorus pesticides in juveniles of Litopenaeus vannamei: alteration of glycogen, triglycerides, and proteins

The presence of pesticides has recently been reported in shrimp farms adjacent to agricultural areas on the east coast of the Gulf of California. This study assessed the possible effect of organophosphorus pesticides in the coastal environment of Sinaloa, México, using the white shrimp Litopenaeus vannamei as a bioindicator since their presence, abundance or behavior indicate some process or state of the system in which they live. Sublethal bioassays were performed on shrimps in intermolt state using commercial brands of organophosphorus pesticides, chlorpyrifos (0.0015 mg l^-1), diazinon (0.0120 mg l^-1), methamidophos (1.207 mg l^-1), azinphos-methyl (0.0101 mg l^-1), and methyl parathion (0.0075 mg l^-1) were tested. Results showed reductions in glycogen, triglycerides, and total protein concentrations in shrimp muscle, except for the diazinon treatments, in which an increase in triglyceride level was detected. The observed alterations in the three cellular components were probably due to the metabolic compensation mechanism of the shrimp in reaction to the stress produced by organophosphorus pesticides, which act as endocrine disruptors. The establishment of continuous environmental monitoring programs of the coastal zone of Northwestern Mexico is strongly recommended.

Alginate from Sargassum siliquosum Simultaneously Stimulates Innate Immunity, Upregulates Immune Genes, and Enhances Resistance of Pacific White Shrimp (Litopenaeus vannamei) Against White Spot Syndrome Virus (WSSV)

Although alginate is known as an immunostimulant in shrimp, the comprehensive and simultaneous study on its activity to resolve the relationship of the hematological parameters, upregulation of immune-related gene expression, and resistance to pathogen has not been found in shrimp. We performed experiments to evaluate the effect and mechanism of alginate from S. siliquosum on Pacific white shrimp immune system. Hematological parameters were examined after oral administration of Na alginate in the shrimp. White spot syndrome virus (WSSV) was injected to the shrimp at 14 days, and its copy number was examined quantitatively (qRT-PCR). Immune-related gene expression was evaluated by qRT-PCR. Alginate increased some hematological immune parameters of shrimp. Before WSSV infection, expression levels of Toll and lectin genes were upregulated. The lectin gene were upregulated post infection, and the Toll gene in all the treatments were downregulated, except the shrimps fed with alginate at 6.0 g kg-1 at 48 h post infection (hpi). The shrimps fed with alginate at 6.0 g kg-1 were the most resistant and gave the least WSSV copy number at 48 hpi. Resistance of shrimps fed the alginate-supplemented diets against WSSV was significantly higher compared to that of the control treatment with 56% and 10% of survival rates, respectively. Oral administration of alginate did not affect the growth and total protein plasma. At 120 h post challenge, alginate treatment at 6.0 g kg-1 exhibited the highest survival rate. It is concluded that oral administration of alginate enhanced the innate immunity by upregulating immune-related gene expression. Consequently, the enhancement of the shrimp innate immunity improves the resistance against WSSV infection.

Toxicity of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in the marine decapod Litopenaeus vannamei

DCOIT (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one) is the main component of SeaNine-211, a new antifouling agent that replaces tributyltin to prevent the growth of undesirable organisms on ships. There have been some studies on the toxicity of DCOIT, but the mechanism of DCOIT's toxicity to crustaceans still requires elucidation. This study examined the chronic toxicity (4 weeks) of 0, 3, 15, and 30 μg/L DCOIT to the Pacific white shrimp (Litopenaeus vannamei) from the aspects of growth and physiological and histological changes in the hepatopancreas and gills. A transcriptomic analysis was performed on the hepatopancreas to reveal the underlying mechanism of DCOIT in shrimp. The exposure to 30 μg/L DCOIT significantly reduced the survival and weight gain of L. vannamei. High Na⁺/K⁺-ATPase activity and melanin deposition were found in the gills after 4 weeks of 15 μg/L or 30 μg/L DCOIT exposure. The highest concentration of DCOIT (30 μg/L) induced changes in hepatopancreatic morphology and metabolism, including high anaerobic respiration and the accumulation of triglycerides. Compared with the exposure to 3 μg/L DCOIT, shrimp exposed to 15 μg/L DCOIT showed more differentially expressed genes (DEGs) than those in the control, and these DEGs were involved in biological processes such as starch and sucrose metabolism and choline metabolism in cancer. The findings of this study indicate that L. vannamei is sensitive to the antifouling agent DCOIT and that DCOIT can induce altered gene expression at a concentration of 15 μg/L and can interfere with shrimp metabolism, growth and survival at 30 μg/L.

Comparative study of the key enzymes and biochemical substances involved in the energy metabolism of Pacific white shrimp, Litopenaeus vannamei, with different ammonia-N tolerances

Pacific white shrimp, Litopenaeus vannamei (9.38 ± 0.17 cm, 10.08 ± 0.35 g), with different ammonia-N tolerances were exposed to NH₃ (1.61 mg/L) for 192 h, and the levels of key enzymes and biochemical substances involved in energy metabolism were compared to assess the role of the regulation of energy metabolism on the shrimp's adaptation to ammonia-N stress. Higher ammonia-N tolerance in the shrimp (Tolerance group) was achieved through nutritional fortification, whereas shrimp that were not nutritionally fortified comprised the Control group. The mortality rates in the Control and Tolerance groups at the end of the period of ammonia-N stress exposure were 64.44% and 40.00%, respectively. Within 1 h of exposure to ammonia-N stress, the glucose concentration in both groups declined rapidly, and no significant difference was detected between the two groups. In general, the triglyceride and cholesterol concentrations in the Control group were higher than those in the Tolerance group, and accumulations and/or fluctuations in these metabolites to varying degrees were observed. The Tolerance group presented higher phosphofructokinase (PFK) and pyruvate kinase (PK) activity compared with the Control group from 1 to 48 h of exposure to ammonia-N stress, whereas the opposite result was observed from 96 to 192 h. Similarly, during exposure to ammonia-N stress, the Tolerance group showed higher and lower lactate dehydrogenase (LDH) activity than the Control group from 1 to 24 h and from 48 to 92 h, respectively. In addition, compared with the Control group, the shrimp in the Tolerance group exhibited higher succinate dehydrogenase (SDH) activity, especially from 48 to 192 h of exposure to ammonia-N stress. The results of this study suggest that anaerobic carbohydrate (in the early stage) and aerobic metabolism (in the late stage) plays an important role in the shrimp's response to ammonia-N stress. In addition, maintenance of the normal operation of lipid metabolism is equally important for improving the tolerance of L. vannamei to ammonia-N stress.

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.

Tyramine's modulation of immune resistance functions in Litopenaeus vannamei and its signal pathway

Tyramine (TA), a neuroactive chemical, plays various important physiological roles in insects by activating distinct G-protein-coupled receptors (GPCRs). In this study, we investigated the effects of by pharmacological injection of TA on immune resistance regulation and its signal pathway in white shrimp Litopenaeus vannamei. Results showed significant increases in the total haemocyte count (THC), semigranular cells (SGCs), granular cells (GCs), phenoloxidase (PO) activity per 50 μL of haemolymph and respiratory bursts (RBs) at 0.5, 1, 2 and/or 4 h; hyaline cells (HCs) at 0.5 h, as well as phagocytic activity (PA) and clearance efficiency (CE) at 2, 4 and/or 8 h, but significantly decreased PO activity per granulocyte at 0.5-2 h for shrimp injected with TA at 100 and 1000 pmol shrimp^-1. Plasma lysozyme activities of TA-injected shrimp were significantly higher than those of the saline control at 1 h. All of the immune parameters had returned to control levels by 8 h after receiving TA except the clearance efficiency, which had returned to its control value by 16 h. The TA injection also significantly decreased the mortality of shrimp challenged with Vibrio alginolyticus. Furthermore, immune parameters of shrimp that received TA at 1000 pmol shrimp^-1 for 1 h were higher than those of shrimp that received the saline. The upregulating effect of TA was blocked by co-injection with phentolamine (Phe) in terms of the THC, HC, SGCs, PO activity, PA and CE; by co-injection with prazosin (Pra) in terms of the THC, HC, SGCs, PO activity, PA and CE; by co-injection with propranolol (Prop) in terms of the PA and CE; and by co-injection with metoprolol (Meto) in terms of the THC and SGCs. The most potent effect in immunocompetence of tested antagonists was Pra, and except for circulating haemocyte, it was Phe. These results suggest that ≤1000 pmol shrimp^-1 of a TA injection mediates transient upregulation of immunity, which in turn promotes the resistance of L. vannamei to V. alginolyticus, and the active effects are mediated via octopamine/tyramine (OA/TA) receptors.