Effects of dietary raw or Enterococcus faecium fermented soybean meal on growth, antioxidant status, intestinal microbiota, morphology, and inflammatory responses in turbot (Scophthalmus maximus L.)

Monascus purpureus M-32 fermented soybean meal improves the growth, immunity parameters, intestinal morphology, disease resistance, intestinal microbiota and metabolome in Pacific white shrimp (Litopenaeus vannamei)

This study was conducted to evaluate the effects of Monascus purpureus M-32 fermented soybean meal (MFSM) on growth, immunity, intestinal morphology, intestinal microbiota, and intestinal metabolome of Pacific white shrimp (Litopenaeus vannamei). Four groups of diets were formulated, including control group (30% fish meal and 30% soybean meal [SBM] included in the basal diet) and three experimental groups which MFSM replaced 20% (MFSM20), 40% (MFSM40), and 60% (MFSM60) of SBM in control group, respectively. Results showed that the soluble proteins larger than 49 kDa in MFSM were almost completely degraded. Meanwhile, the crude protein, acid-soluble protein, and amino acid in MFSM were increased. The results of shrimp culture experiment showed that the replacement of SBM with MFSM decreased FCR (P < 0.001) and content of malondialdehyde (P = 0.007) in the experimental groups, and increased weight gain rate (P = 0.006), specific growth rate (P = 0.002), survival rate (P = 0.005), intestinal villus height (P < 0.001), myenteric thickness (P = 0.002), the activities of superoxide dismutase (P = 0.002), and lysozyme (P = 0.006) in experimental groups, as well as increased content of calcium (Ca2+) and phosphorus (PO 4 3 - ) in blood and muscle, and enhanced resistance to Vibrio parahaemolyticus infection. The gut microbiota of MFSM groups was significantly different from that of the control group, and the abundance of Actinobacteria and Verrucomicrobia increased significantly in the MFSM60 group, whereas Proteobacteria and Firmicutes decreased. Compared with the control group, there were significant changes in the levels of several intestinal metabolites in the MFSM60 group, including leukotriene C5, prostaglandin A1, taurochenodeoxycholic acid, carnosine, and itaconic acid. The fermentation of SBM by the strain M. purpureus M-32 has the potential to enhance the nutritional quality of SBM, promote the growth of L. vannamei, boost immune response, improve intestinal morphology and microbiota composition, as well as influence intestinal metabolites.

Fermentation of Plant-Based Feeds with Lactobacillus acidophilus Improves the Survival and Intestinal Health of Juvenile Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System

This study evaluated the effect of fermentation with Lactobacillus acidophilus on the biochemical and nutritional compositions of a plant-based diet and its effects on the productive performance and intestinal health of juvenile Nile tilapia (Oreochromis niloticus) reared in a biofloc technology (BFT) system. The in vitro kinetics of feed fermentation were studied to determine the L. acidophilus growth and acidification curve through counting the colony-forming units (CFUs) mL-1 and measuring the pH. Physicochemical and bromatological analyses of the feed were also performed. Based on the microbial growth kinetics results, vegetable-based Nile tilapia feeds fermented for 6 (FPB6) and 18 (FPB18) h were evaluated for 60 days. Fermented diets were compared with a positive control diet containing fishmeal (CFM) and a negative control diet without animal protein (CPB). Fermentation with L. acidophilus increased lactic acid bacteria (LAB) count and the soluble protein concentration of the plant-based feed, as well as decreasing the pH (p < 0.05). FPB treatments improved fish survival compared with CPB (p < 0.05). Fermentation increased feed intake but worsened feed efficiency (p < 0.05). The use of fermented feeds increased the LAB count and reduced pathogenic bacteria both in the BFT system's water and in the animals' intestines (p < 0.05). Fermented plant-based feeds showed greater villi (FPB6; FPB18) and higher goblet cell (FPB6) counts relative to the non-fermented plant-based feed, which may indicate improved intestinal health. The results obtained in this study are promising and show the sustainable potential of using fermented plant-based feeds in fish feeding rather than animal protein and, in particular, fishmeal.

Microbiome and metabolome in home-made fermented soybean foods of India revealed by metagenome-assembled genomes and metabolomics

Grep-chhurpi, peha, peron namsing and peruñyaan are lesser-known home-made fermented soybean foods prepared by the native people of Arunachal Pradesh in India. Present work aims to study the microbiome, their functional annotations, metabolites and recovery of metagenome-assembled genomes (MAGs) in these four fermented soybean foods. Metagenomes revealed the dominance of bacteria (97.80 %) with minor traces of viruses, eukaryotes and archaea. Bacillota is the most abundant phylum with Bacillus subtilis as the abundant species. Metagenome also revealed the abundance of lactic acid bacteria such as Enterococcus casseliflavus, Enterococcus faecium, Mammaliicoccus sciuri and Staphylococcus saprophyticus in all samples. B. subtilis was the major species found in all products. Predictive metabolic pathways showed the abundance of genes associated with metabolisms. Metabolomics analysis revealed both targeted and untargeted metabolites, which suggested their role in flavour development and therapeutic properties. High-quality MAGs, identified as B. subtilis, Enterococcus faecalis, Pediococcus acidilactici and B. velezensis, showed the presence of several biomarkers corresponding to various bio-functional properties. Gene clusters of secondary metabolites (antimicrobial peptides) and CRISPR-Cas systems were detected in all MAGs. This present work also provides key elements related to the cultivability of identified species of MAGs for future use as starter cultures in fermented soybean food product development. Additionally, comparison of microbiome and metabolites of grep-chhurpi, peron namsing and peruñyaan with that of other fermented soybean foods of Asia revealed a distinct difference.

Synbiotic Agents and Their Active Components for Sustainable Aquaculture: Concepts, Action Mechanisms, and Applications

Aquaculture is a fast-emerging food-producing sector in which fishery production plays an imperative socio-economic role, providing ample resources and tremendous potential worldwide. However, aquatic animals are exposed to the deterioration of the ecological environment and infection outbreaks, which represent significant issues nowadays. One of the reasons for these threats is the excessive use of antibiotics and synthetic drugs that have harmful impacts on the aquatic atmosphere. It is not surprising that functional and nature-based feed ingredients such as probiotics, prebiotics, postbiotics, and synbiotics have been developed as natural alternatives to sustain a healthy microbial environment in aquaculture. These functional feed additives possess several beneficial characteristics, including gut microbiota modulation, immune response reinforcement, resistance to pathogenic organisms, improved growth performance, and enhanced feed utilization in aquatic animals. Nevertheless, their mechanisms in modulating the immune system and gut microbiota in aquatic animals are largely unclear. This review discusses basic and current research advancements to fill research gaps and promote effective and healthy aquaculture production.

The effects of sodium butyrate (NaB) combination with soy saponin dietary supplementation on the growth parameters, intestinal performance and immune-related genes expression of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂)

Soy saponins are generally known to have negative effects on growth and the intestines of aquatic animals, and appropriate levels of sodium butyrate (NaB) may provide some mitigating effects. We investigated the effects of low and high levels of soy saponin and the protective effects of NaB (based on high level of soy saponin) on growth, serum cytokines, distal intestinal histopathology, and inflammation in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). The experiment included four groups: fishmeal group (FM, 0.00% saponin and 0.00% NaB), low saponin group (SL, 0.30% saponin and 0.00% NaB), high saponin group (SH, 1.50% saponin and 0.00% NaB) and high saponin with NaB group (SH-NaB, 1.50% saponin and 0.13% NaB). The results showed compared to FM, the final body weight (FBW) and weight gain (WG) were significantly higher and lower in SL and SH, respectively (P < 0.05). Compared to SH, the FBW and WG were significant higher in SH-NaB (P < 0.05). In the serum, compared to FM, the interferon γ (IFN-γ) and interleukin-1β (IL-1β) levels in SH were significantly increased (P < 0.05). Compared to SH, the IFN-γ level was significantly decreased in SH-NaB (P < 0.05). In the distal intestine, based on Alcian Blue-Periodic Acid-Schiff (AB-PAS) observation, the goblet cell/μm was significantly increased and decreased in the SL and SH, respectively, compared to FM. The intestinal diameter/plica height ratio in the SH was significantly higher than those in the FM, SL and SH-NaB (P < 0.05). The NO and ONOO- levels in the SH were significantly higher than that in FM and SL (P < 0.05). At the transcriptional level in the distal intestine, compared to FM, the mRNA levels of tumor necrosis factor (tnfα), il1β, interleukin-8 (il8) and ifnγ were significantly up-regulated in the SH (P < 0.05). Compared to the SH, tnfα, il8 and ifnγ were significantly down-regulated in the SH-NaB (P < 0.05). Compared to the FM, the mRNA levels of claudin3, claudin15, zo2 and zo3 were significantly up-regulated in the SL (P < 0.05). The mRNA levels of occludin, claudin3, claudin12, claudin15, zo1, zo2 and zo3 were significantly down-regulated in the SH compared to the FM (P < 0.05). Additionally, compared to the SH, the mRNA levels of occludin, claudin3, claudin12, claudin15, zo1, zo2 and zo3 were significantly up-regulated in the SH-NaB (P < 0.05). After the 7-day Vibrio parahaemolyticus challenge test, the survival was significantly higher and lower in the SL and SH, respectively, compared to FM (P < 0.05). Overall, low and high levels of soy saponins had positive and negative effects on growth, disease resistance, serum cytokines, and distal intestinal development and anti-inflammation, respectively, in hybrid grouper. NaB effectively increased disease resistance and improved distal intestinal inflammation in hybrid grouper, but the effects of NaB were mainly observed in improving distal intestinal tight junctions.

Comprehensive study on the effect of dietary leucine supplementation on intestinal physiology, TOR signaling and microbiota in juvenile turbot (Scophthalmus maximus L.)

Intestinal damage and inflammation are major health and welfare issues in aquaculture. Considerable efforts have been devoted to enhancing intestinal health, with a specific emphasis on dietary additives. Branch chain amino acids, particularly leucine, have been reported to enhance growth performance in various studies. However, few studies have focused on the effect of leucine on the intestinal function and its underlying molecular mechanism is far from fully illuminated. In the present study, we comprehensively evaluated the effect of dietary leucine supplementation on intestinal physiology, signaling transduction and microbiota in fish. Juvenile turbot (Scophthalmus maximus L.) (10.13 ± 0.01g) were fed with control diet (Con diet) and leucine supplementation diet (Leu diet) for 10 weeks. The findings revealed significant improvements in intestinal morphology and function in the turbot fed with Leu diet. Leucine supplementation also resulted in a significant increase in mRNA expression levels of mucosal barrier genes, indicating enhanced intestinal integrity. The transcriptional levels of pro-inflammatory factors il-1β, tnf-α and irf-1 was decreased in response to leucine supplementation. Conversely, the level of anti-inflammatory factors tgf-β, il-10 and nf-κb were up-regulated by leucine supplementation. Dietary leucine supplementation led to an increase in intestinal complement (C3 and C4) and immunoglobulin M (IgM) levels, along with elevated antioxidant activity. Moreover, dietary leucine supplementation significantly enhanced the postprandial phosphorylation level of the target of rapamycin (TOR) signaling pathway in the intestine. Finally, intestinal bacterial richness and diversity were modified and intestinal bacterial composition was re-shaped by leucine supplementation. Overall, these results provide new insights into the beneficial role of leucine supplementation in promoting intestinal health in turbot, offering potential implications for the use of leucine as a nutritional supplement in aquaculture practices.

Effects of plant-derived protein and rapeseed oil on growth performance and gut microbiomes in rainbow trout

BACKGROUND

Rainbow trout (Oncorhynchus mykiss) is becoming popular with the increased demand for fish protein. However, the limited resources and expense of fish meal and oil have become restrictive factors for the development of the rainbow trout related industry. To solve this problem, plant-derived proteins and vegetable oils have been developed as alternative resources. The present study focuses on evaluating the effects of two experimental diets, FMR (fish meal replaced with plant-derived protein) and FOR (fish oil replaced with rapeseed oil), through the alteration of the gut microbiota in triploid rainbow trout. The commercial diet was used in the control group (FOM).

RESULTS

Amplicon sequencing of the 16S and 18S rRNA genes was used to assess the changes in gut bacteria and fungi. Our analysis suggested that the α-diversity of both bacteria and fungi decreased significantly in the FMR and FOR groups, and β-diversity was distinct between FOM/FMR and FOM/FOR based on principal coordinate analysis (PCoA). The abundance of the Planctomycetota phylum increased significantly in the FMR group, while that of Firmicutes and Bacteroidetes decreased. We also found that the fungal phylum Ascomycota was significantly increased in the FMR and FOR groups. At the genus level, we found that the abundance of Citrobacter was the lowest and that of pathogenic Schlesneria, Brevundimonas, and Mycoplasma was highest in the FMR and FOR groups. Meanwhile, the pathogenic fungal genera Verticillium and Aspergillus were highest in the FMR and FOR groups. Furthermore, canonical correspondence analysis (CCA) and network analysis suggested that the relatively low-abundance genera, including the beneficial bacteria Methylobacterium, Enterococcus, Clostridium, Exiguobacterium, Sphingomonas and Bacteroides and the fungi Papiliotrema, Preussia, and Stachybotrys, were positively correlated with plant protein or rapeseed oil. There were more modules that had the above beneficial genera as the hub nodes in the FMR and FOR groups.

CONCLUSIONS

Our study suggested that the FMR and FOR diets could affect the gut microbiome in rainbow trout, which might offset the effects of the dominant and pathogenic microbial genera. This could be the underlying mechanism of explaining why no significant difference was observed in body weight between the different groups.

Aquafeed fermentation improves dietary nutritional quality and benefits feeding behavior, meat flavor, and intestinal microbiota of Chinese mitten crab (Eriocheir sinensis)

Normally, proper fermentation can be an efficient and widely used method to improve feed quality in animal rearing; however, the studies on crustaceans, especially Eriocheir sinensis, remain limited. This study aimed to investigate whether feed fermentation could meliorate dietary nutritional value and benefit E. sinensis rearing. First, non-fermented feed (NFD) and fermented feed (FD) were produced and assessed, respectively. Then, the "Y" maze feed choice behavior test (180 times; 30 times, 6 rounds) was conducted to assess the attractiveness of these 2 feeds for crabs. Finally, a total of 80 crabs (44.10 ± 0.80 g) were randomly assigned into 2 groups with 4 replicates, and fed the experimental diets for 8 weeks to evaluate the effects of each feed on growth, antioxidant capacity, meat flavor, and intestinal microbiota. In this study, FD showed higher levels of crude protein (P < 0.01), soluble protein (P < 0.01), amino acids (P < 0.05), lactic acid (P < 0.001), and lower levels of crude fiber (P < 0.05) and antinutritional factors (agglutinin, trypsin inhibitor, glycinin, and β-conglycinin) (P < 0.001) than NFD. Additionally, FD was more attractive to crabs than NFD (P < 0.01) and it stimulated the appetite of crabs more than NFD (P < 0.05). The growth performance, feed efficiency, and digestive enzyme activity of FD-fed crabs were significantly higher than those of NFD-fed crabs (P < 0.05). The electronic sensory measurements and free amino acid profiles revealed that the FD diet had positive impacts on the meat flavor of crabs, particularly in "sweet" and "umami" tastes. Moreover, the antioxidant capacity of FD-fed crabs was significantly higher than that of NFD-fed crabs (P < 0.05). Fermented feed also affected the diversity and composition of intestinal microflora. The functional prediction of microbial communities showed that crabs fed FD had a better microecological environment in the intestine. In conclusion, the fermentation of aquafeed could be an effective approach to enhance feed quality and therefore benefit E. sinensis rearing.

Enhancement of Soybean Meal Alters Gut Microbiome and Influences Behavior of Farmed Atlantic Salmon (Salmo salar)

Atlantic salmon (Salmo salar) is one of the worlds most domesticated fish. As production volumes increase, access to high quality and sustainable protein sources for formulated feeds of this carnivorous fish is required. Soybean meal (SBM) and soy-derived proteins are the dominant protein sources in commercial aquafeeds due to their low-cost, availability and favorable amino acid profile. However, for Atlantic salmon, the inclusion of soybean meal (SBM), and soy protein concentrate (SPC) in certain combinations can impact gut health, which has consequences for immunity and welfare, limiting the use of soy products in salmonid feeds. This study sought to address this challenge by evaluating two gut health-targeted enhancements of SBM for inclusion in freshwater phase salmon diets: enzyme pre-treatment (ETS), and addition of fructose oligosaccharide (USP). These were compared with untreated soybean meal (US) and fish meal (FM). This study took a multi-disciplinary approach, investigating the effect on growth performance, gut microbiome, and behaviors relevant to welfare in aquaculture. This study suggests that both enhancements of SBM provide benefits for growth performance compared with conventional SBM. Both SBM treatments altered fish gut microbiomes and in the case of ETS, increased the presence of the lactic acid bacteria Enterococcus. For the first time, the effects of marine protein sources and plant protein sources on the coping style of salmon were demonstrated. Fish fed SBM showed a tendency for more reactive behavior compared with those fed the FM-based control. All fish had a similar low response to elicited stress, although ETS-fed fish responded more actively than US-fed fish for a single swimming measure. Furthermore, SBM-fed fish displayed lower repeatability of behavior, which may indicate diminished welfare for intensively farmed fish. The implications of these findings for commercial salmonid aquaculture are discussed.

Evaluation of Fermented Soybean Meal to Replace a Portion Fish Meal on Growth Performance, Antioxidant Capacity, Immunity, and mTOR Signaling Pathway of Coho Salmon (Oncorhynchus kisutch)

In this study, we evaluated the effects of fermented soybean meal (FSBM) or/and unfermented SBM replacing a portion of fish meal (FM) on the growth performance, antioxidant capacity, immunity, and mechanistic target of rapamycin (mTOR) signaling pathway of juvenile coho salmon (Oncorhynchus kisutch). Four groups of juvenile coho salmon (initial weight 152.23 ± 3.21 g) in triplicate were fed for 12 weeks on four different iso-nitrogen and iso-lipid experimental diets: G0 diet (28% FM protein, control group), G1 diet (18% FM protein and 10% SBM protein), G2 diet (18% FM protein, 5% SBM protein, and 5% FSBM protein), and G3 diet (18% FM protein and 10% FSBM protein). The main results were compared with the G0 diet; the weight gain rate, specific growth rate, and condition factor of juveniles in G3 were increased significantly (p < 0.05). The content of muscle crude protein, the total protein, glucose, albumin, total cholesterol in serum, and the total antioxidant capacity in the liver of juveniles in G3 was increased significantly (p < 0.05). The activities of pepsin, trypsin, α-amylase, and lipase in the intestine, the superoxide dismutase, catalase, and alkaline phosphatase in the liver of juveniles in G3 were increased significantly (p < 0.05). The expression levels of phosphatidylinositide 3-kinases, serine/threonine kinase, mTOR, and ribosomal protein S6 kinase 1 genes in the liver of juveniles in G3 were upregulated significantly (p < 0.05). The feed coefficient ratio, viscerosomatic index, the contents of muscle moisture, and malondialdehyde in the liver of juveniles in G3 were decreased significantly (p < 0.05). The expression levels of tumor necrosis factor α, interleukin 1β, and interleukin 6 genes in the liver of juveniles in G3 were downregulated significantly (p < 0.05). However, there was no significant effect (p > 0.05) on the survival rate, food intake, and muscle crude lipid and ash of juveniles among the experimental groups. In conclusion, FSBM to replace a portion FM had a positive effect on the growth performance, protein deposition, antioxidant enzyme activity, digestive enzyme activity, protein synthesis, and immune-related genes of juvenile coho salmon.

A comparative study on effects of dietary three strains of lactic acid bacteria on the growth performance, immune responses, disease resistance and intestinal microbiota of Pacific white shrimp, Penaeus vannamei

The present study evaluated the growth performance, immune responses, disease resistance and intestinal microbiota in Penaeus vannamei fed diets supplemented with three strains of lactic acid bacteria (LAB). The basal diet (control, CO) supplemented with Lactobacillus plantarum W2 (LA), Pediococcus acidilactici Nj (PE), Enterococcus faecium LYB (EN) and florfenicol (FL), respectively, formed three LAB diets (1 × 10¹⁰ cfu kg^-1) and a florfenicol diet (15 mg kg^-1, positive control), were fed to shrimp for 42 days. Results indicated that specific growth rate, feed efficiency rate, and disease resistance of shrimp against Vibrio parahaemolyticus in the treatment groups were significantly improved versus the control (P < 0.05). Compared with the control, acid phosphatase, alkaline phosphatase, phenonoloxidase, total nitric oxide synthase, peroxidase, superoxide dismutase activities, total antioxidant capacity, and lysozyme content in the serum and the relative expression levels of SOD, LZM, proPO, LGBP, HSP70, Imd, Toll, Relish, TOR, 4E-BP, eIF4E1α and eIF4E2 genes in the hepatopancreas of LAB groups were enhanced to various extents. Intestinal microbiota analysis showed that the LA and EN groups significantly improved microbial diversity and richness, and LAB groups significantly altered intestinal microbial structure of shrimp. At the phylum level, the Verrucomicrobiota in the LA and PE groups, the Firmicutes in the EN group, and the Actinobacteriota in the PE and EN groups were enriched. Moreover, the CO group increased the proportion of potential pathogens (Vibrionaceae and Flavobacteriaceae). The potential pathogen (Vibrio) was reduced, and potential beneficial bacteria (Tenacibaculum, Ruegeria and Bdellovibrio) were enriched in response to dietary three strains of LAB. When the intestinal microbiota homeostasis of shrimp is considered, L. plantarum and E. faecium showed better effects than P. acidilactici. However, due to the concerns on the possible potential risks of E. faecium strains to human health, L. plantarum W2 is more suitable for application in aquaculture than E. faecium LYB. Considering collectively the above, Lactobacillus plantarum W2 could be applied as better probiotic to improve the growth performance, non-specific immunity, disease resistance and promote intestinal health of P. vannamei.

Effects of a Phytogenic Supplement Containing Olive By-Product and Green Tea Extracts on Growth Performance, Lipid Metabolism, and Hepatic Antioxidant Capacity in Largemouth Bass (Micropterus salmoides) Fed a High Soybean Meal Diet

A 10-week growth trial was conducted to investigate the effects of a phytogenic feed additive (PFA) containing olive by-products and green tea extracts supplemented to a reduced fishmeal/high soybean meal diet on the growth performance, hepatic antioxidant capacity, lipid metabolism, and liver health of largemouth bass (Micropterus salmoides). Three experimental diets were tested: (1) a control high fishmeal (40%) and low soybean meal (15.57%) diet (named HFM), (2) a reduced fishmeal (30%) and high soybean meal (30.97%) diet (named HSB), and (3) a HSB diet supplemented with the PFA at 500 mg/kg (named HSB+P). Each diet was assigned to four replicate tanks, each containing 30 largemouth bass (initial body weight, IBW = 48.33 ± 0.01 g). The results showed that increasing the soybean meal content in the diet did not negatively affect growth performance, whereas supplementation with PFA significantly increased weight gain and specific growth rate of largemouth bass compared to both HFM and HSB groups. Reducing fishmeal and increasing soybean meal in the diet caused oxidative stress with a higher content of ROS in the liver. However, the hepatic antioxidant capacity was enhanced, with reduced ROS and increased GSH-Px levels in the HSB+P group. Moreover, the decrease of plasma TG, LDL-C, and LDL-C/TC, and downregulation of lipogenesis and cholesterol synthesis gene expression in liver, indicated that supplementation with the PFA improved fish lipid metabolism. Protein retention efficiency was also significantly increased in largemouth bass fed the diet with PFA supplementation, which regulated (enhanced) AKT-mTOR phosphorylation. These results clearly indicated that a PFA containing olive by-product and green tea extracts can positively improve growth performance, protein retention efficiency, antioxidant capacity, and lipid metabolism of largemouth bass fed a reduced fishmeal/high soybean meal diet.

Fermented Soybean Meal (FSBM) in African Catfish (Clarias gariepinus) Diets: Effects on Growth Performance, Fish Gut Microbiota Analysis, Blood Haematology, and Liver Morphology

The study revealed the potential of fermented soybean meal (FSBM) as a fish meal (FM) replacement in African catfish (Clarias gariepinus) feed formulation. Five isonitrogenous diets (32% crude protein) were prepared with five different levels of FSBM as FM replacement, namely 0% FSBM (T1), 40% FSBM (T2), 50% FSBM (T3), 60% FSBM (T4), and 70% (T5). The experimental fish was given the formulated diet for eight consecutive weeks. At the end of the feeding trial, the fish were subjected to growth performance, blood parameters, blood chemical, liver histology, and gut microbiota assessment. The study findings demonstrated that the experimental fish that received the T2 diet exhibited significantly higher (p < 0.05) growth performance. Experimental fish that received diet T2 had significantly higher (p < 0.05) white blood cell (WBC) and significantly lower (p < 0.05) in terms of cholesterol (CHOL), albumin (ALB), globulin (GLOB), and total protein (TP). The replacement of FSBM to FM significantly affected liver morphology on the sinusoid, vacuole, nucleus, and erythrocytes. Gut microbiota composition analysis showed a significantly high abundance (p < 0.05) of Akkermansia muciniphila in the experimental fish that received the T2 diet. The gut microbiota indicates that the experimental fish is in a healthy condition. In conclusion, replacing 40% FSBM with FM in aquafeed could enhance C. gariepinus growth performance and health conditions.

Food Protein-Derived Antioxidant Peptides: Molecular Mechanism, Stability and Bioavailability

The antioxidant activity of protein-derived peptides was one of the first to be revealed among the more than 50 known peptide bioactivities to date. The exploitation value associated with food-derived antioxidant peptides is mainly attributed to their natural properties and effectiveness as food preservatives and in disease prevention, management, and treatment. An increasing number of antioxidant active peptides have been identified from a variety of renewable sources, including terrestrial and aquatic organisms and their processing by-products. This has important implications for alleviating population pressure, avoiding environmental problems, and promoting a sustainable shift in consumption. To identify such opportunities, we conducted a systematic literature review of recent research advances in food-derived antioxidant peptides, with particular reference to their biological effects, mechanisms, digestive stability, and bioaccessibility. In this review, 515 potentially relevant papers were identified from a preliminary search of the academic databases PubMed, Google Scholar, and Scopus. After removing non-thematic articles, articles without full text, and other quality-related factors, 52 review articles and 122 full research papers remained for analysis and reference. The findings highlighted chemical and biological evidence for a wide range of edible species as a source of precursor proteins for antioxidant-active peptides. Food-derived antioxidant peptides reduce the production of reactive oxygen species, besides activating endogenous antioxidant defense systems in cellular and animal models. The intestinal absorption and metabolism of such peptides were elucidated by using cellular models. Protein hydrolysates (peptides) are promising ingredients with enhanced nutritional, functional, and organoleptic properties of foods, not only as a natural alternative to synthetic antioxidants.

Dietary Lactoferrin Supplementation Improves Growth Performance and Intestinal Health of Juvenile Orange-Spotted Groupers (Epinephelus coioides)

A 56-day feeding trial was conducted to investigate the effects of dietary lactoferrin (LF) supplementation on the growth performance and intestinal health of juvenile orange-spotted groupers fed high-soybean-meal (SBM) diets. The control diet (FM) and high-soybean-meal diet (SBM60) were prepared to contain 480 g/kg protein and 110 g/kg fat. Three inclusion levels of 2, 6, and 10 g/kg LF were added into the SBM60 to prepare three diets (recorded as LF2, LF6, and LF10, respectively). The results showed that the supplementation of LF in SBM60 increased the growth rate in a dose-dependent manner. However, the feed utilization, hepatosomatic index, whole-body proximate composition, and the abundance and diversity of intestinal microbiota did not vary across the dietary treatments (p > 0.05). After the dietary intervention with LF, the contents of the intestinal malondialdehyde, endotoxin, and d-lactic acid, as well as the plasma low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and total cholesterol were lower, and the intestinal activities of the glutathione peroxidase, lipase, trypsin, and protease were higher in the LF2-LF10 groups than that in the SBM60 group (p < 0.05). The supplementation of LF in SBM60 increased the muscle layer thickness of the middle and distal intestine and the mucosal fold length of the middle intestine vs. the SBM60 diet (p < 0.05). Furthermore, the supplementation of LF in SBM60 resulted in an up-regulation of the mRNA levels for the IL-10 and TGF-β1 genes and a down-regulation of the mRNA levels of the IL-1β, IL-12, IL-8, and TNF-α genes vs. the SBM60 diet (p < 0.05). The above results showed that a dietary LF intervention improves the growth and alleviates soybean meal-induced enteritis in juvenile orange-spotted groupers. The dietary appropriate level of LF was at 5.8 g/kg, through the regression analysis of the percent weight gain against the dietary LF inclusion levels.

Lactiplantibacillus plantarum 0111 Protects Against Influenza Virus by Modulating Intestinal Microbial-Mediated Immune Responses

There are some limitations of traditional influenza vaccines concerning novel mutant strains. Therefore, it is particularly important to develop preventive means for antigen-unrelated types of influenza viruses. Recent studies have shown that probiotics can modulate the immune system and reduce the severity of viral infections. In this study, we investigated the potential of Lactiplantibacillus plantarum 0111 against influenza virus H9N2. Challenge experiments showed that L. plantarum 0111 pretreatments could effectively improve mice’s survival rate and weight loss and reduce the inflammatory cytokines IL-6 and TNF-α in the lungs and bronchoalveolar lavage fluid (BALF) along with the degree of lung and intestinal injury. FMT experiment demonstrates that the protective effect produced by L. plantarum 0111 is associated with gut microorganisms. In addition, 16S high-throughput sequencing of the mouse intestinal microbiota showed that L. plantarum 0111 remodeled the intestinal microbiota after H9N2 infection and maintained the gut microbiota balance. In a mouse model, the oral administration of L. plantarum 0111 increased IFN-β expression in the serum and BALF. At the same time, the transcript levels of IFN-β and related ISGs in the intestine and lungs of mice were also increased. In addition, the activation and polarization of T cells in mesenteric lymph nodes (MLNs) and the spleen were detected by flow cytometry, and the results showed that L. plantarum 0111 modulated cytokines in T cells and increased IgA expression in B cells in the MLNs and spleen. Thus, L. plantarum 0111 may improve gut microbiota-mediated immune responses and thus, resist infection by the influenza virus, and it could be used as an effective preventive measure against the influenza virus.

Dietary Inclusion of Seabuckthorn (Hippophae rhamnoides) Mitigates Foodborne Enteritis in Zebrafish Through the Gut-Liver Immune Axis

To help prevent foodborne enteritis in aquaculture, several feed additives, such as herbal medicine, have been added to fish diets. Predictions of effective herb medicines for treating fish foodborne enteritis from key regulated DEGs (differentially expressed genes) in transcriptomic data can aid in the development of feed additives using the Traditional Chinese Medicine Integrated Database. Seabuckthorn has been assessed as a promising candidate for treating grass carp soybean-induced enteritis (SBMIE). In the present study, the SBMIE zebrafish model was used to assess seabuckthorn’s therapeutic or preventative effects. The results showed that intestinal and hepatic inflammation was reduced when seabuckthorn was added, either pathologically (improved intestinal villi morphology, less oil-drops) or growth-related (body fat deposition). Moreover, seabuckthorn may block the intestinal p53 signaling pathway, while activating the PPAR signaling pathway and fatty acid metabolism in the liver. 16S rRNA gene sequencing results also indicated a significant increase in OTU numbers and skewed overlapping with the fish meal group following the addition of seabuckthorn. Additionally, there were signs of altered gut microbiota taxa composition, particularly for reduced TM7, Sphingomonas, and Shigella, following the addition of seabuckthorn. Hindgut imaging of fluorescent immune cells in SBMIE larvae revealed the immune regulatory mechanisms at the cellular level. Seabuckthorn may significantly inhibit the inflammatory gathering of neutrophils, macrophages, and mature T cells, as well as cellular protrusions’ formation. On the other hand, in larvae, seabuckthorn inhibited the inflammatory aggregation of lck⁺ T cells but not immature lymphocytes, indicating that it affected intestinal adaptive immunity. Although seabuckthorn did not affect the distribution of intestinal CD4⁺ cells, the number of hepatic CD4⁺ cells were reduced in fish from the seabuckthorn supplementation group. Thus, the current data indicate that seabuckthorn may alleviate foodborne gut-liver symptoms by enhancing intestinal mucosal immunity and microbiota while simultaneously inhibiting hepatic adipose disposition, making it a potential additive for preventing fish foodborne gut-liver symptoms.

Fermentation of Soybean Meal with Lactobacillus acidophilus Allows Greater Inclusion of Vegetable Protein in the Diet and Can Reduce Vibrionacea in the Intestine of the South American Catfish (Rhamdia quelen)

Simple Summary

There is a demand to replace fishmeal with protein sources of plant origin in fish feeds. Biotechnology strategies, such as fermentation, can improve the bioavailability of plant proteins and decrease the presence of antinutrients, optimizing the results obtained. Fermented soybean meal has already been evaluated for different fish species as a replacement for fishmeal, and there is evidence that it can improve the intestinal health of animals. Lactobacillus acidophilus is a strain used as a probiotic in fish feeding but it remains to be evaluated as a potential fermentation bacterium for feed ingredients. This study aimed to evaluate the effect of diets containing different inclusion levels (0%, 7%, 14%, 21% and 28%) of soybean meal fermented by L. acidophilus (SMFL) on the zootechnical performance and intestinal health of South American catfish juveniles (Rhamdia quelen). The inclusion of SMFL up to 21% in replacement of fish meal did not affect the zootechnical performance of fish and also decreased the concentration of Vibrionaceae bacteria present in the intestine compared to the control group. The results demonstrate that fermentation with L. acidophilus enables greater inclusion of soybean protein in South American catfish diets and promotes the control of intestinal pathogenic bacteria.

Abstract

The objective of this study was to evaluate the effect of diets containing different inclusion levels (0%, 7%, 14%, 21% and 28%) of soybean meal fermented by Lactobacillus acidophilus (SMFL) on the zootechnical performance and intestinal health of South American catfish juveniles (Rhamdia quelen). The experimental design was completely randomized with five treatments and four replications and lasted 56 days. Five isoproteic (39% crude protein) and isoenergetic (4300 kcal of gross energy kg⁻¹) diets were formulated where SMFL was included in replacement of fish meal. Two hundred forty South American catfish juveniles (3.0 ± 0.5 g) were distributed in 20 tanks (70 L) connected in a recirculation aquaculture system. At the end of the experiment, the inclusion of SMFL up to 21% in replacement of fish meal did not affect the zootechnical performance and also decreased the concentration of Vibrionaceae bacteria present in the intestine compared to the control group. The amount of total lactic and heterotrophic bacteria, the enzymatic activity and the intestinal morphometry did not differ between dietary treatments. The results demonstrate that fermentation with Lactobacillus acidophilus enables greater inclusion of soybean protein in South American catfish diets and promotes the control of intestinal pathogenic bacteria.

Effects of Replacing Dietary Fish Meal by Soybean Meal Co-Fermented Using Bacillus subtilis and Enterococcus faecium on Serum Antioxidant Indices and Gut Microbiota of Crucian Carp Carassius auratus

Fermented soybean meal (FSM) is an important feed material that can replace fish meal to solve the shortage of animal protein. To improve the utilization of FSM, we optimized the co-fermentation conditions of soybean meal using Bacillus subtilis and Enterococcus faecium and studied the effects of replacing fish meal with different proportions of FSM on serum antioxidant indices and gut microbiota (GM) composition of crucian carp (Carassius auratus). Our results showed that the co-fermentation of soybean meal was the most effective when the ratio of B. subtilis X-2 and E. faecium X-4 was 2:3, glucose addition was 4.5%, KH2PO4 addition was 0.15%, MgSO4·7H2O addition was 0.1%, anhydrous sodium acetate addition was 0.4%, fermentation time was 120 h, and the solid–water ratio was 1:1. Replacing 40% fish meal with FSM in the feed significantly improved the serum T-AOC, POD, and IgM levels in C. auratus. Although there were significant differences in the midgut and hindgut microbiota structures of C. auratus, the addition of FSM to the feed did not cause significant differences in the GM structure, whether in the midgut or hindgut. Therefore, 40% FSM is the most suitable substitute for fish meal in the feed of C. auratus.

Microplastics in fish meals: An exposure route for aquaculture animals

Microplastics (MPs) are widely detected in many marine fishes. Fish meal contaminated by MP may constitute a potential threat to aquaculture animals. This study analyzed the characteristics of MP in fish meals from ten major fish meal-producing countries around the world. Microplastics were isolated from fish meal, examined under a microscope and identified using Fourier transform infrared microspectroscopy (μ-FT-IR). The results showed that MP pollution was widely detected in fish meal samples from ten countries. The average MP abundance of fish meals was 5.5 ± 1.6 items/g, with higher levels in China, Peru and Myanmar, which might be related to the high pollution level in fish and their habitats. In isolated MPs, fibers were the main shape type, and the most common size was 500-1000 μm. A total of 6 polymers were identified, with cellophane (CP), polypropylene (PP) and polyethylene teraphalate (PET) being the most common types. The total amount of MP ingestion from fish meals by different cultured animals was also estimated, with Atlantic salmon Salmon salar ingesting the largest number of MPs (9361 items), and red swamp crayfish Procambarus clarkii ingesting the smallest number of MPs (19 items). Thus, fish meal constitutes an important exposure route of MPs for aquaculture animals. The results of this study will provide a basis to assess the potential health risks of MPs in fish meals around the world.

Dietary gamma-aminobutyric acid ameliorates growth impairment and intestinal dysfunction in turbot (Scophthalmus maximus L.) fed a high soybean meal diet

Over-substitution of fishmeal with soybean meal (SBM) commonly induces inferior growth and intestinal dysfunction in fish. This study aims to evaluate whether dietary gamma-aminobutyric acid (GABA) could ameliorate the adverse effects in turbot fed a high-SBM diet (HSD). Two hundred and seventy turbots were randomly divided into three treatment groups including turbots fed on a control diet (CNT, containing 60% fishmeal), an HSD (with 45% fishmeal protein replaced by SBM), and an HSD supplemented with GABA (160 mg kg-1) for 53 days. The growth and feed utilization parameters were calculated and the intestinal antioxidant status, inflammation, apoptosis, and microbiota were evaluated using assay kits, histological analysis, qRT-PCR, high throughput sequencing, and bioinformatics analysis. The results showed that GABA ameliorated HSD-induced growth impairment and enhanced feed intake of turbot. GABA ameliorated HSD-induced intestinal oxidative stress and apoptosis by restoring the MDA content, CAT and T-AOC activities, and apoptosis-related gene (Bcl-2, Bax, Bid, and Caspase-3) expressions to similar levels to those in the CNT group. GABA also alleviated HSD-induced intestinal inflammation through down-regulating the expressions of TNF-α, IL-1β, and NF-κB p65 and up-regulating the expression of TGF-β1. Furthermore, GABA reversed HSD-induced microbiota dysbiosis through regulating the overall bacterial richness and dominative bacterial population. Spearman's correlation analysis indicated that the altered microbiota was closely associated with growth and intestinal function. Collectively, GABA could ameliorate HSD-induced intestinal dysfunction via relieving oxidative stress, inflammation, apoptosis and microbiota dysbiosis, and these findings would contribute to a better understanding of the function of GABA in the fish intestine.

Medical Image Recognition Technology in the Effect of Substituting Soybean Meal for Fish Meal on the Diversity of Intestinal Microflora in Channa argus

Purpose

To study the application of medical image recognition technology based on backpropagation neural network (BPNN) in the effect of soybean meal replacing fish meal on intestinal microbial diversity of Channa argus and to evaluate the application value of this intelligent algorithm, Channa argus was fed with different contents of soybean meal instead of fish meal.

Methods

After intestinal samples were collected and bacteria were isolated, microscopic imaging was performed, and the images were classified and identified. BPNN was constructed to perform denoising, smoothing, and segmentation.

Results

After BPNN processing, the bacteria were completely separated from the original image background, and the bacteria was in the closed state, which was beneficial to feature extraction and species recognition. If there were 2 hidden layer nodes, the segmentation accuracy of bacterial microscopic images was the highest, up to 97.3%. With the replacement ratio of fish meal increased, the species of intestinal microbiome gradually enriched, and the relative abundance of intestinal microbiome was higher after fish meal was completely replaced by soybean meal (replacement). The intestinal microbial enzyme activities were affected by different fish meal and soybean meal contents in the diet. The glutamate transaminase and adenosine deaminase activities were increased after the replacement and were higher than those before the replacement, with statistically significant differences (P < 0.05).

Conclusion

Replacement of fish meal with soybean meal has a significant effect on the intestinal flora diversity of Channa argus, and there is a close relationship between them. The image recognition technology based on BPNN has high recognition rate and segmentation accuracy for microbiological microscopic images.

Recent progress in the understanding of the gut microbiota of marine fishes

As the significance of the gut microbiota has become increasingly realized, a large number of related studies have emerged. With respect to the gut microbial composition of fish, the predominant gut microbes and core gut microbiota have been reported by many researchers. Our understanding of fish gut microbiota, especially its functional roles, has fallen far behind that of terrestrial vertebrates, although previous studies using gnotobiotic zebrafish models have revealed that the gut microbiota performs a significant role in gut development, nutrient metabolism and immune responses. Given that environmental factors of marine habitats are very different from those of freshwater habitats, a distinct difference may exist in the gut microbiota between freshwater and marine fish. Therefore, this review aims to address the advances in marine fish gut microbiota in terms of methodologies, the gut microbial composition, and gnotobiotic models of marine fish, the important factors (host genotype and three environmental factors: temperature, salinity and diet) that drive marine fish gut microbiota, and significant roles of the gut microbiota in marine fish.

Effects of Potential Probiotic Enterococcus casseliflavus (EC-001) on Growth Performance, Immunity, and Resistance to Aeromonas hydrophila Infection in Common Carp (Cyprinus carpio)

The effects of different levels of dietary Enterococcus casseliflavus (EC-001), as a potential probiotic, were investigated on the growth performance, hemato-biochemical parameters, immune responses, and resistance to Aeromonas hydrophila infection in common carp (Cyprinus carpio) fingerlings. Accordingly, fish (N = 720; 12.0 ± 0.5 g) were distributed into four treatments receiving different dietary levels of E. casseliflavus, EC-001 (0 [control], 1 × 10⁷, 10⁸, and 10⁹ CFU g^-1 feed), for 8 weeks. The fish fed with a diet containing 10⁹ CFU g^-1 showed the highest weight gain and specific growth rate, along with the lowest feed conversion ratio, compared with the control group (P < 0.05). Red and white blood cells, hemoglobin, hematocrit, neutrophils, and monocytes significantly increased in the fish fed with 1 × 10⁸ and 10⁹ CFU g^-1 (P < 0.05). Dietary inclusion of 1 × 10⁸ and 10⁹ CFU g^-1 significantly increased serum total protein, albumin, and immunoglobulin content (P < 0.05). Feeding the fish with 1 × 10⁹ CFU g^-1 resulted in a significant increase in serum and skin mucus lysozyme activity compared with the other groups (P < 0.05). Complement component 3 and skin mucus protease activity were also significantly higher in all the fish treated with dietary E. casseliflavus (EC-001) compared with the control group (P < 0.05). The cumulative mortality in the treated fish was lower (ranging from 10 to 22%) than the control group (31%) after challenging the fish with A. hydrophila infection, while the fish fed with E. casseliflavus (EC-001) at 1 × 10⁹ CFU g^-1 exhibited the lowest mortality rate (P < 0.05). In conclusion, our results revealed the potential probiotic effects of E. casseliflavus (EC-001) for enhancing growth performance, immunity, and disease resistance of common carp.