Functional additives play a significant role in improving health problems caused by high-fat diet (HFD) in farmed fish species. This study aimed to evaluate the effects of trans-cinnamaldehyde (TCA) on liver and gut health of HFD-feeding zebrafish. The results showed that triglyceride (TAG), serum alanine aminotransferase (ALT) and aspartic aminotransferase (AST) concentrations were significantly reduced in the TCA50 group. Liver malondialdehyde (MDA) content was significantly reduced, whereas higher activities of glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT) and total antioxidant capacity (T-AOC) were recorded in the TCA50 group. Besides, TCA promoted the expression of proteins related to the antioxidant stk11/ampkα/nrf2 pathway. Serum lipopolysaccharides (LPS) content and expression of pro-inflammatory genes were notably reduced in the TCA groups, and the TCA50 group improved the intestinal villi and goblet cells in the midgut and hindgut. Zebrafish survival rate was increased in TCA groups after challenged with Aeromonas veronii Hm091 and Aeromonas hydrophila NJ-1. The relative abundances of Fusobacteriota and Cetobacterium were elevated in the TCA50 group. The gut microbiota altered by TCA50 group indirectly improved the antioxidant capacity of germ-free (GF) zebrafish, through the antioxidant gsk3β/nrf2 pathway, with Cetobacterium somerae potentially acting as the primary effector bacterium in enhancing the antioxidant capacity of the fish. Feeding of 50 mg/kg TCA directly to GF zebrafish activated the stk11/ampkα/nrf2 pathway and enhanced the expression of antioxidant enzymes. In conclusion, dietary supplementation with 50 mg/kg TCA alleviated HFD-induced oxidative stress in zebrafish via direct activation of stk11/ampkα/nrf2 and gut microbiota-mediated activation of gsk3β/nrf2 pathways.

The purpose of this study was to evaluate the effects of Eucommia ulmoides leaf extract (ELE) on growth performance, liver and gut health, gut microbiota profile and disease resistance of largemouth bass. The basal diet was enriched with ELE at 0 g/kg (control), 1.0 g/kg (ELE1.0), 2.0 g/kg (ELE2.0), and 3.0 g/kg (ELE3.0). Largemouth bass (initial body weight of 9.25 +/- 0.03 g) were assigned to one of the four diets and fed for five weeks. According to the result, ELE supplementation significantly increased weight gain (WG) and reduced feed conversion ratio (FCR) compared with controls (P < 0.05). In addition, ELE reduced hepatic inflammation and the mRNA level of nuclear factor kappa b p65 (nf kappa b). ELE improved intestinal structural integrity and notably upregulated the mRNA and protein expression of hypoxia-inducible factor 1-alpha (hif1 alpha), while nf-kappa b expression was significantly downregulated in the intestine of ELE2.0 and ELE3.0 groups. Moreover, the results of gut microbiota 16S rRNA sequencing analysis revealed that Bacillus showed a rising trend in the ELE2.0 group and principal coordinate analysis (PCoA) revealed a distinct shift in microbial community structure in the ELE 2.0 group. Furthermore, the ratio of (Firmicutes+ Bacteroidetes+ Fusobacteria) to Proteobacteria was significantly higher in the ELE 2.0 group compared to the control. The survival rate (SR) of largemouth bass in ELE supplementation groups were significantly improved following Aeromonas veronii NJ-1 and Aeromonas hydrophila Hm091 challenge. Taking together, dietary ELE enhanced growth, liver health, intestinal structure, bacterial disease resistance, and improved the gut microbiota structure in largemouth bass, with 2.0 g/kg identified as the optimal inclusion level.

The present study evlatuated the effects of moist fermented feed (MFF) substituted for dry pellet feed on hepatopancreas and intestine health and intestinal microbiota of Pacific white shrimp (Litopenaeus vannamei). A total of 150 shrimp (1.56 +/- 0.02 g) were fed with moist fermented feed once every two days (MFF0.5/4), once a day (MFF1/4), twice a day (MFF2/4) and four times a day (MFF4/4) or the control diet (dry pellet feed) for 8 weeks. MFF had no effect on the weight gain rate (WGR) of shrimp, but showed a notable lower survival rate (SR) and feed conversion ratio (FCR) in the MFF4/4 group (P < 0.05). The levels of TAG and R-cells in the hepatopancreas of the MFF1/4 group were markedly lower (P < 0.05). Additionally, the hepatopancreas level of T-AOC in MFF1/4 and the activity of SOD in MFF1/4 and MFF2/4 groups were significantly increased (P < 0.05). The expressions of nf-kb and penaeidin-3a and crustin genes in the hepatopancreas of shrimp fed on MFF0.5/4 and MFF1/4 were notably upregulated (P < 0.05). Relative to the control group, the expression of tgf-beta in MFF1/4, Penaiedin-3a and Peritrophic in MFF0.5/4 and MFF1/4 groups were noteworthy upregulated in the intestine (P < 0.05). Moreover, MFF0.5/4, MFF1/4 and MFF2/4 levels improved the intestinal microbiota of shrimp by decreasing the abundance of opportunistic pathogen Vibrio and Pseudomonas genus. In summary, feeding MFF once a day or once every two days improved the hepatopancreatic and intestinal health of shrimp, and feeding MFF once a day seems better for promoting the health of shrimp.

P-Hydroxycinnamic acid (PCA), a natural phenolic compound, exhibits multifaceted biological activities, including antioxidant and metabolic regulatory properties in mammals, whereas its role in fish is rarely reported. To investigate whether PCA can alleviate the negative effects caused by high-fat diets on fish liver health and disease resistance, here we used zebrafish as experimental animals. In this study, six zebrafish diets, including basal diet, high-fat diet (HFD), and HFD supplemented with PCA at 500, 1000, 1500, or 2500 mg/kg and assigned as CK, HFD, PCA0.5, PCA1, PCA1.5, and PCA2.5, respectively. Following a 6-week feeding trial on zebrafish, PCA supplementation significantly attenuated hepatic triglyceride (TAG) accumulation without compromising growth performance. With increasing the level of PCA, the expression of inflammatory factors showed an upregulating trend. Serum biomarkers of liver injury (ALT, AST) were markedly reduced in PCA-treated groups, concomitant with enhanced hepatic antioxidant capacity (CAT, GR) and upregulated the expression of anti-inflammatory cytokines (tgf-β). Notably, PCA administration improved survival rates following a dual challenge with Aeromonas veronii HM091 and Aeromonas hydrophila NJ-1. These findings demonstrate that PCA0.5 supplementation effectively mitigates HFD-induced oxidative stress and hepatic steatosis while enhancing innate immunity in zebrafish.

The increasing use of plant-based raw materials in aquatic feed has led to a growing concern about the harmful effects of mycotoxins on aquatic animals. This study aimed to evaluate the supplementation of yeast cell wall extract (YCWE) on the growth performance, liver and intestine health, and gut microbiota of largemouth bass (Micropterus salmoides) fed with aflatoxin B1 (AFB1), and deoxynivalenol (DON) contaminated feeds. AFB1, DON and YCWE were supplemented to the basic formula feed at different concentrations to develop eight dietary groups and M. salmoides were fed for 8 weeks. Results showed that the inclusion of YCWE in mycotoxins-contaminated diets had no effect on the growth performance but significantly affected the immunity and antioxidant capacity of M. salmoides (P < 0.05). The overall changes in serum biochemical indicators were not significant, except that the ALT/AST activities were significantly higher (P < 0.05) under the mycotoxin challenge, and significantly lower in 0.2 % YCWE treatment group. Furthermore, the expression of genes related to liver and intestine inflammation (pro-inflammatory factors nf-kb, tnf-a, il-1 beta, il-6, il-8, ifn-gamma and anti-inflammatory factors il-10, tgf-beta), and antioxidant regulatory factors nrf2/keap1 showed an up-regulation trend, and the content of the lipid metabolite MDA was notably higher under mycotoxin challenge and YCWE treatments (P < 0.05). Moreover, the supplementation of YCWE significantly alleviated the inflammatory responses (P < 0.05), enhanced the activities of antioxidant enzymes (SOD, CAT) (P < 0.05) and the expression of tight junction proteins genes occludin, claudin4, and zo-1, and reduced the content of MDA, suggesting that mycotoxin challenge tested herein could activate the inflammatory response and lead to oxidative stress while YCWE could improve liver and intestinal health in mycotoxin challenged fish. Additionally, metataxonomic profiling of the gut microbiota showed that YCWE supplemented fish had higher bacterial richness and diversity, suggesting its role in reducing gut microbial dysbiosis. In summary, mycotoxins had negative effects on the health of M. salmoides, while the supplementation of YCWE could alleviate such negative effects in a dose-dependent manner, demonstrating that YCWE can be a remediation strategy for mycotoxins decontamination in aquaculture.

The importance of the gastrointestinal microbiota (GM) in health and disease is widely recognized. Although less is known in fish than in mammals, advances in molecular techniques, such as 16S rRNA sequencing, have facilitated characterization of fish GM, comprising resident autochthonous and transient allochthonous bacteria. The microbial diversity and composition are strongly influenced by diet. High-protein diets, including alternative ingredients like plant and insect proteins, modify GM, impacting beneficial bacteria e.g. Cetobacterium. Lipids affect microbial metabolism and short-chain fatty acid (SCFA) production, while excessive carbohydrates can disrupt GM balance, causing enteritis. Dietary additives, including probiotics, prebiotics, and antibiotics, effectively modulate GM. Probiotics enhance immunity and growth, prebiotics support beneficial bacteria, and antibiotics, though effective against pathogens, disrupt microbial diversity and may promote antibiotic resistance. Environmental factors, such as temperature, salinity, and pollution, significantly influence GM. Elevated temperatures and salinity shifts alter microbial composition, and pollutants introduce toxins that compromise intestinal function and microbial diversity. Stress and pathogen infections further destabilize GM, often favoring pathogenic bacteria. GM communicates with the host via metabolites such as SCFAs, bile acids, and neurotransmitters, regulating appetite, energy metabolism, immunity, and neural functions. Additionally, GM influences the immune system by interacting with epithelial cells and stimulating immune responses. Despite recent advances, further research is needed to elucidate species-specific mechanisms underlying GM-host interactions, the ecological implications of GM diversity, and its applications in aquaculture to optimize fish health and performance.

Nowadays, the fermented products of probiotics have been playing a significant role in aquaculture and become an emerging research interest. This study evaluated the 0, 0.2, 0.3 and 0.4 g/kg solid state fermentation product of Bacillus velezensis T23 supplemented diets (39 % crude protein and 10 % crude fat) on the growth, lipid metabolism, liver and intestinal health, and gut microbiota of Cyprinus carpio (2.51 +/- 0.01 g) by physiobiochemical, histomorphological and gut microbiome methods. The results showed that in the 0.4 T23 group, the weight gain was significantly increased (p p < 0.05), compared to the control. . In the 0.3 and 0.4 T23 groups, the expressions of lipogenesis-related genes (fas, fas , acc, srebp and ppar gamma) were significantly down-regulated, while the expressions of lipolysis-related ( ppar alpha, lpl, , fabp1 and apo-po) ) genes were up-regulated. Furthermore, the levels of serum ALT and AST were decreased notably (p p < 0.05), whereas T-AOC and SOD activity were increased significantly in the 0.3 and 0.4 T23 groups, compared with the control. Pro-inflammatory genes ( nf-kb , tnf-alpha, and il-1 beta) ) were downregulated in 0.3 and 0.4 T23 groups (p p < 0.05). Anti-inflammatory related genes ( il-10 and tgf-beta) ) were upregulated in 0.3 T23 groups. This result had been supported by liver histomorphology that T23 diets had decreased the levels of liver health biomarkers and intestinal injury and improve the hepatic antioxidant capacity. Dietary supplementation of T23 at a level of 0.3 g/kg increased alpha-diversity- diversity and the relative abundance of Fusobacteriota (phylum) and Cetobacterium (genus). The ratio of "(Fusobacteriota+Firmicutes+Bacteroidota)/ +Firmicutes +Bacteroidota)/ Proteobacteria" in 0.3 and 0.4 T23 groups was significantly increased, compared with the control group. Hence, this study clarified that the addition of solid state fermentation product of B. velezensis T23 to the diet (0.3 and 0.4 g/kg) of common carp improves inflammatory response, liver and gut health, and modulates the intestinal microbiota of carp positively.

This review synthesizes the research progress in applying omics to aquatic animal nutrition, highlighting their advantages as well as current limitations, and outlines future directions for development. Traditional nutritional research is often hampered by environmental variability, low precision, and the complexity of nutrient interactions across different tissues. The advent of high-throughput sequencing, bioinformatics, and functional genomics has driven the rapid emergence of various omics fields, such as genomics, transcriptomics, proteomics, metabolomics, and microbiomics. These technologies overcome the limitations of traditional research methods, becoming powerful tools for investigating the regulatory mechanisms of nutrition in aquatic animals. Genomics and transcriptomics reveal genetic responses of aquatic animals to nutritional interventions, whereas proteomics and metabolomics enable large-scale analysis of proteins and metabolites, illuminating physiological changes under various nutritional conditions. Moreover, microbiomics provides crucial insights into the interactions between gut microbiota and host nutrient metabolism and immunity. Key applications such as gene editing and protein post-translational modification analysis further elucidate molecular mechanisms of nutritional regulation in fish. Despite significant advances, omics still faces persistent challenges, including technological complexity, ethical concerns, underdeveloped regulatory systems, ecological safety risks, and issues related to data storage and sharing. Addressing these through technological innovation, improved regulatory frameworks, and the expansion of application areas will be crucial for the sustainable advancement of omics in aquatic animal nutrition research.

The application of commensal probiotic bacteria is one of the preferable green feed additives for antibiotic substitution in aquaculture, while the application methods and detailed action mechanisms of commensal bacteria isolated from aquatic animals are not consistent with normal mammalian-derived probiotics. The purpose of this study was to evaluate the effects of solid-state fermentation product of autochthonous Bacillus velezensis T23 on improving hepatic steatosis, liver antioxidation capacity, gut injury and gut microbiota profile of genetically improved farmed tilapia (GIFT, Oreochromis niloticus). The T23 probiotic was added to the basal diet at a level of 0.00, 0.05, 0.1, 0.2 and 0.3 g/kg to develop five experimental diets, respectively. After 4 weeks of the feeding trial, the results showed that T23 supplementation notably reduced the hepatocytes vacuolization and the content of liver TAGs by downregulated the mRNA expression of the lipogenesis gene (fas), while upregulated the mRNA expression of lipid degradation genes (cpt1 and ppar alpha) (p < 0.05). Compared with the control, the 0.3T23 group showed significantly upregulated expression levels of anti-inflammatory cytokine genes (tgf-beta and il-10) in the liver of the fish (p < 0.05). Besides, the activities of antioxidase SOD and CAT were significantly upregulated in T23 treatment groups, compared with the control (p < 0.05). Fish groups fed with 0.2 g/kg and 0.3 g/kg T23 supplemented diet also exhibited significantly lower intestinal injury and intestinal inflammation via upregulating the expression of tight junction protein gene claudin, anti-inflammatory factor gene il-10 (p < 0.05). However, markedly downregulation of the mRNA level of pro-inflammatory cytokine il-1 beta (p < 0.05) was observed in 0.05 and 0.3T23 groups, compared with the control. 16S rRNA sequencing analysis data on gut microbiota indicated that supplementation of T23 at lower levels (0.05, 0.1 and 0.2) resulted in a remarkable elevation of the abundance of phylum Firmicutes and reduced the abundance of Proteobacteria, and the ratio of (Firmicutes +Bacteroidota +Fusobacteria) /Proteobacteria. On the contrary, feeding with 0.3T23 negatively affects the gut microbiota diversity and structure of tilapia. Therefore, a 0.2 g/kg dose is suggested to supplement the diet of Nile tilapia to improve liver health and modulate the gut microbiota profile of the fish positively. Overall, these findings provide a shred of beneficial evidence of the application of B. velezensis T23 as a green feed additive to improve the productivity and profitability of tilapia farming.

BACKGROUND:Feeding adult zebrafish a diet supplemented with quenching enzyme AiiO-AIO6 (AIO6) for 3 wk improved the growth performance and disease resistance. However, when the feeding period was extended to 8 wk, zebrafish's disease resistance to Aeromonas veronii decreased. OBJECTIVES:We investigated the mechanisms of the reduced disease resistance of zebrafish induced by feeding on an AIO6 supplemented diet for a long term (8 wk) and assessed the effectiveness of feed additives in restoring the low disease resistance. METHODS:One-month-old (adult) zebrafish were fed with a basal diet and the basal diet supplemented with AIO6 (10 U/g) for 8 wk (experiment 1). Furthermore, the zebrafish larvae model (experiment 2) was developed and used to study the mechanisms of how AIO6 affected disease resistance (experiment 3). We also investigated the effectiveness of selected prebiotic tributyrin, β-glucan or mannan in activating gut microbiota- HIF1α to restore the low disease resistance of adult zebrafish fed with AIO6 for 8 wk (experiment 4). Lastly, the effects of Bacillus subtilis in activating the gut microbiota-HIF1α and improving the low disease resistance of zebrafish larvae induced by AIO6 were examined (experiment 5). RESULTS:Feeding adult zebrafish with AIO6 for 8 wk promoted growth but disordered the gut microbiota and reduced disease resistance. The zebrafish larvae model confirmed that feeding AIO6 for 2 d increased disease resistance, whereas 7 d decreased the resistance by suppressing HIF1α. Using a germ-free zebrafish larvae model, we also demonstrated that AIO6-induced gut microbiota mediated inhibition of HIF1α. Furthermore, zebrafish fed on the AIO6-containing diet supplement with tributyrin, β-glucan, mannan, or Bacillus subtilis activated the gut microbiota-HIF1α axis to reverse the low resistance caused by AIO6. CONCLUSIONS:Activating the gut microbiota-HIF1α axis has a vital role in improving intestinal health and restores the low resistance to Aeromonas veronii caused by improper administration of dietary AIO6 in zebrafish.

BACKGROUND:Intestinal and liver damage induced by a high-fat diet (HFD) is a major problem in farmed fish. Cetobacterium somerae is a native beneficial bacterium to many fish species, including zebrafish, a model animal for nutrition studies of economically important fish species. OBJECTIVES:The aim of this study was to investigate the mechanisms how mannose and tributyrin affect the growth of C. somerae and its role in ameliorating HFD-induced liver and intestinal damage, and gut microbiota dysbiosis of zebrafish. METHODS:One-month-old zebrafish were fed for 4 wk with Control (5.77% fat), HFD (14.64% fat), or HFD supplemented with 1.0% mannose (experiment 1) and 0.1% tributyrin (experiment 2). Then, a combination treatment of mannose and tributyrin was tested with an HFD and compared their effects with the previous single additive groups (experiment 3). Finally, the effects of Cetobacterium and Plesiomonas on alleviating HFD-induced liver steatosis were investigated using germ-free (GF) zebrafish (experiment 4). RESULTS:When Cetobacterium abundance was low in the gut of HFD-fed zebrafish, the prebiotic mannose could not improve the growth of Cetobacterium to elicit any beneficial effects. Supplementation with tributyrin created an appropriate anaerobic gut environment for Cetobacterium growth by upregulating the expression of the hif1a gene by 86.4% (P < 0.05). The combination of mannose and tributyrin increased the abundance of Cetobacterium by 309.8% compared with the HFD group. In addition, the combination treatment reduced triacylglycerol, Alanine aminotransferase, and aspartic aminotransferase levels (0.61-, 0.46-, and 0.55-fold, respectively; P < 0.05) and improved HFD-induced liver damage. Furthermore, intestinal damage was improved as verified with a lower level of serum LPS (0.59-fold, P < 0.05). After transferring Cetobacterium into GF zebrafish, the liver lipid accumulation caused by HFD was reduced by 10.9% (P < 0.05). CONCLUSIONS:The combination of mannose and tributyrin enhanced the growth of Cetobacterium and its benefits in improving HFD-induced liver and intestinal damage.

Vaccines are one of the most practical means to stop the spreading of Aeromonas veronii in aquaculture. In this study, virulence factor aerolysin mutant NTaer which has lost its hemolytic activity was used as a target antigen. Pichia pastoris constitutive secretory expression NTaer (GS115-NTaer) was used as a potential safe oral vaccine to evaluate its effectiveness on zebrafish immunity. The result shows that vaccination of GS115- NTaer for four weeks did not affect the growth performance of the host, while eliciting an effective immune protective response. Compared with the control group, the GS115-NTaer could significantly up-regulate the relative expression level of the intestinal tight junction protein 1α (TJP1α) gene, and significantly increased the contents of lysozyme (LYZ), complement C3 and C4 in the gut, indicating that the innate immune response of the fish was activated. The relative gene expression levels of macrophage-expressed gene 1 (MPEG1) and T cell receptor (TCR-α) in the gut, and MPEG1, CD4, CD8, TCR-α, GATA3, and T-bet in the spleen were all increased significantly, indicating that the cellular immune response of the fish was activated. Furthermore, the contents of serum IgM and intestinal mucosa IgZ antibodies were significantly increased, which showed that humoral immunity was also activated. Moreover, inoculation with GS115-NTaer significantly changed the structure of gut microbiota. In particular, the relative ratio of (Firmicutes + Fusobacteriota + Bacteroidota)/Proteobacteria was significantly higher than that of the control and GS115 groups. Lastly, the vaccinated fish were challenged with A. veronii, and the relative percent survival of GS115 and the GS115-NTear groups was 14.28

AbstractLactobacillus rhamnosus GG (LGG), the well‐characterized human‐derived probiotic strain, possesses excellent properties in the maintenance of intestinal homeostasis, immunoregulation and defense against gastrointestinal pathogens in mammals. Here, we demonstrate that the SpaC pilin of LGG causes intestinal epithelium injury by inducing cell pyroptosis and gut microbial dysbiosis in zebrafish. Dietary SpaC activates Caspase‐3−GSDMEa pathways in the intestinal epithelium, promotes intestinal pyroptosis and increases lipopolysaccharide (LPS)‐producing gut microbes in zebrafish. The increased LPS subsequently activates Gaspy2−GSDMEb pyroptosis pathway. Further analysis reveals the Caspase‐3−GSDMEa pyroptosis is initiated by the species‐specific recognition of SpaC by TLR4ba, which accounts for the species‐specificity of the SpaC‐inducing intestinal pyroptosis in zebrafish. The observed pyroptosis‐driven gut injury and microbial dysbiosis by LGG in zebrafish suggest that host‐specific beneficial/harmful mechanisms are critical safety issues when applying probiotics derived from other host species and need more attention.

This study aimed to elucidate the effects of dietary fermented products of Bacillus velezensis T23 on the growth, immune response and gut microbiota in Pacific white shrimp (Litopenaeus vannamei). Shrimp were fed with diets containing fermentation products of B. velezensis T23 at levels of (0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 g/kg) for 4 weeks, to assess the influence on shrimp growth. The results showed that 0.3 and 0.4 g/kg T23 supplementation improved shrimp growth and feed utilization. Based on these results we selected these three diets (Control, 0.3T23 and 0.4T23) to assess the effect on immune response and gut microbiota of shrimp. Compared with the control, the 0.3T23 and 0.4T23 groups enhanced lipase and α-amylase activities in the gut significantly. Moreover, the 0.4T23 group decreased TAG and MDA levels in hepatopancreas, ALT and AST levels of serum significantly (P < 0.05). In hepatopancreas, CAT and SOD activities were improved observably and the MDA content was reduced markedly in both T23 groups. The expressions of antimicrobial related genes, Cru and peroxinectin in the 0.3T23 group, and proPO and peroxinectin in the 0.4T23 group were up-regulated remarkably (P < 0.05). Moreover, hepatopancreas of shrimp fed with a diet amended with T23 showed a significant down-regulated expression of nf-kb and tnf-α genes, while expressions of tgf-β was considerably up-regulated. Furthermore, serum LPS and LBP contents were reduced markedly in T23 groups. Intestinal SOD and CAT were noteworthy higher in T23 groups (P < 0.05). In the intestine of shrimp fed on the diet enriched with T23 the expression of nf-κb and tnf-α exhibited markedly down-regulated , whereas hif1α was up-regulated (P < 0.05). Besides, in the intestine of shrimp grouped under T23, Cru and peroxinectin genes were markedly up-regulated (P < 0.05). Dietary 0.3 g/kg T23 also upregulated the ratio of Rhodobacteraceae to Vibrionaceae in the gut of the shrimp. Taken together, the inclusion of B. velezensis T23 in the diet of shrimp enhanced the growth and feed utilization, enhanced hepatopancreas and intestine health.

This study aimed to investigate the effects of solid-state fermentation products of yeast (SFPY) on liver and intestinal health and disease resistance of common carp (Cyprinus carpio). A total of 200 common carp with an initial average weight of 2.55 ± 0.004 g were divided into 5 groups (4 replications per group and 10 fish per replication), and were fed with one of five diets, including a control diet and 4 diets supplemented with 2‰ (Y2), 3‰ (Y3), 4‰ (Y4), or 5‰ (Y5) SFPY, respectively, for 8 weeks. Results indicated that, the addition of SFPY to the diet of common carp did not affect the growth performance or survival rate of fish (P = 0.253). Interestingly, with the addition of SFPY, the triacylglycerol (TAG) content of the liver presented a linear decreasing tendency (P = 0.004), with significantly decreased in Y4 and Y5 groups (P = 0.035) compared with control. Serum lipopolysaccharide (LPS) content and diamine oxidase (DAO) activity presented a negative linear relationship with the addition of SFPY (P = 0.015, P = 0.030), while serum lipopolysaccharide binding protein (LBP) content first decreased and then increased (P < 0.001). The total antioxidant capacity (T-AOC) in the intestine of fish increased continuously with increasing SFPY supplementation (P = 0.026), reaching the highest level in Y5 group. The villus height in all experimental groups were significantly higher than that in the control group (P < 0.001). Furthermore, compared to the control, adding 3‰ SFPY to the control diet of common carp significantly increased the relative abundance of Fusobacteria (P = 0.018) and decreased that of Proteobacteria (P = 0.039) at phylum level, and increased the relative abundance of Cetobacterium (P= 0.018) and decreased that of Shewanella (P = 0.013) at genus level. Compared with the control, the relative mRNA expression level of spring viraemia of carp virus N protein (SVCV-n) in the kidney was lower than that of the control group without significance and bottomed out in Y4 group (P = 0.138). In conclusion, dietary SFPY enhanced the SVCV resistance capacity of common carp by improving liver and intestinal health and modulating the gut microbiota. Thus, SFPY is a potential feed additive to be used in aquaculture to reduce the huge economic loss of common carp due to SVCV disease. Based on liver TAG content and intestinal villus height, the optimal addition level of SFPY was 3.02‰ and 2.72‰, respectively.

Probiotics are important for the normal physiological functions of fish and are used as feed additives in many aquatic animals. The purpose of this study is to explore the effects of dietary bacterial culture of fengycinproducing Bacillus subtilis (B. subtilis) on growth performance, intestinal and hepatopancreas health, intestinal microbiota and disease resistance of common carp (Cyprinus carpio). Three diets were formulated with supplementation of bacterial culture of fengycin-producing B. subtilis at 0, 0.3 and 0.5 g/kg levels, and these diets were defined as control, BS0.3 and BS0.5, respectively. After 6-week feeding, the infiltration of inflammatory cells was improved in the BS0.3 and BS0.5 groups. And the anti-inflammatory cytokines (interleukin (IL)-10 and tumor growth factor beta (TGF-beta) were prominently increased in the hepatopancreas of fish fed with dietary B.subtilis diets (P < 0.05). The activity of lysozyme, the levels of complement component (C) 3 and C4 were remarkably increased in the hepatopancreas and intestine of fish fed with B.subtilis supplemented diets (P < 0.05). Histological (intestinal villi height was increased in BS0.3 and BS0.5 groups) (P < 0.05) and the expression of the gut physical barrier-related genes (Zona occludens-1 (ZO-1) and occludin) were increased in the B.subtilis supplemented groups (P < 0.05). The expression of pro-inflammatory cytokines (IL-1 beta, IL-6 and tumor necrosis factor alpha (TNF-alpha) and anti-inflammatory cytokines (IL-10 and TGF-beta) were remarkably up-regulated in the intestine of fish fed with BS0.3 diet (P < 0.05), while the expression of IL-6 was remarkably diminished in the intestine of fish fed with BS0.5 diet (P < 0.05). Besides, the intestinal microbiota analysis illustrated that in the intestine of the fish groups fed with BS0.3 and BS0.5 diets, the abundance of Fusobacteriota and Cetobacterium were prominently increased (P < 0.05). After challenged with Aeromonas veronii Hm091, the survival rate of fish fed with BS0.3 diet was markedly improved (P < 0.05). Based on these results, supplementation of bacterial culture of fengycinproducing B. subtilis at a level of 0.3 g/kg has beneficial effects on immunity, intestinal microbiota, and disease resistance of common carp.

Microbial oil, as an alternative to fish oil, animal and vegetable oils in aquafeeds, have a great potential to fulfil the high demand for lipid sources in the fast-growing aquaculture. However, their use as a feed ingredient in aquaculture is not common. For that, Rhodotorula toruloides (51.90 % lipid) was used to replace 0.00 % (control), 9.38 % (RT3), 18.75 % (RT6), 37.50 % (RT9), and 56.25 % (RT18) of the lard and soybean oils commonly used in aquaculture in the diet of zebrafish. After 6 weeks of feeding, compared with the control group, (1) the FBW and WGR were significantly increased (p<0.05) p <0.05) in RT9 group, (2) the content of C18:1 and C18:3 fatty acids were increased, while that of C18:0, C18:2, and C20:4 were decreased in the muscle of zebrafish, indicating that the fatty acid content of the feed affect the muscle content of fatty acids, (3) the intestinal lipase activity was markedly elevated in RT9 group (p<0.05), p <0.05), (4) in RT9 and RT18 groups the content of AST was significantly reduced (p<0.05), p <0.05), (5) the content of TAG in the liver was significantly reduced in RT6, RT9 and RT18 groups (p<0.05), p <0.05), probably due to the down-regulation of the lipid synthesis-related gene dgat2 and up-regulation of the lipolysis-related gene ucp2, , (6) the expression of il-8 in the intestine was notably downregulated in RT9 and RT18 groups (p<0.05), p <0.05), whereas the expression of inhibitory gene il-10 was significantly upregulated in RT9 group (p<0.05), p <0.05), (7) feeding with R. toruloides reduced the relative abundance of Proteobacteria and Vibrio spp, , while increasing the abundance of Firmicutes. In sum, the replacement of R. toruloides at a level of 37.50 % can improve the growth, digestive enzyme activity, liver health and gut microbiota profile of zebrafish fed with high- fat diet and can be used to replace the oil sources from other unsustainable ingredients in aquafeed.

Immunostimulants were widely used in aquafeed due to their multiple important functions, including promoting growth, enhancing non-specific defence mechanisms and resisting infectious diseases. But the efficiencies of the positive effects of immunostimulants were affected by the duration of the administration and their dose. Short-term and normal-dose of immunostimulants promoted the growth and enhance non-specific immunity of aquatic animals. However, improper use led to several immune disorders, including immune tolerance, immune exhaustion and over-immunity. The application of two immunostimulant diets in rotation technique and the intermittent use of immune stimulant diets may solve the problems associated with immune disorders, but this application method will be limited by both species and immunostimulants. The occurrence of immune disorders is accompanied by different degrees of gut microbiota dysbiosis, especially significantly up-regulated the abundance of Proteobacteria. Besides, the gut symbiotic microbiota plays a significant role in host immunity. Consequently, the regulation of gut microbiota may be an effective way to modulate immune disorders caused by improper use of polysaccharide immunostimulants. Regulating the gut microbiota not only solves the negative effects caused by improper use of immunostimulants without restrictions on both species and immunostimulants, but also has the advantage of simplicity and convenience compared to conventional approaches. In summary, this article reviews the possible negative effects caused by improper use of immunostimulants on aquatic animals and compares regular approaches with regulating gut microbiota. And gut microbiota maybe be used as a therapeutic target to improve immune disorders caused by immunostimulants in aquatic animals.

Tilapia (Oreochromis sp.) are cultured in many countries of the world. Its production is increasing from time to time to fulfill the demand for fish for the fast-growing population of the world. The significant importance of intestinal microbiota in several fish conditions including growth, digestion, energy homeostasis, immunity, and gut-brain axis were reported in a plethora of studies. Characterization of the intestinal microbiota is important to deal with the detailed function of these microbes. The majority of the bacteria species found in the intestine of fish are not culturable and to date, due to the advancement of molecular techniques including denaturing gradient gel electrophoresis (DGGE), temperature gradient gel electrophoresis (TGGE), and next-generation sequencing (NGS) has been employed to investigate and characterize intestinal microbiota. Researchers have been working to increase the production and productivity of tilapia in aquaculture by altering the different microorganisms found in the intestinal of the fish. Studies showed types of diets and their ingredient compositions have a significant role in improving and modulation of the intestinal microbiota of tilapia. Furthermore, the role of several “-biotics” including prebiotics, probiotics, paraprobiotics, and postbiotics in the improvement of the intestinal microbiota was described in many studies. The significance of dealing with intestinal microbiota is to provide a scientific basis for the establishment of useful approaches for the effective manipulation of these microorganisms to improve fish health and increase production. The intimate knowledge of the usefulness of intestinal microbiota on the overall fitness of tilapia is necessary. Therefore, the objective of this review was to entirely understand the importance and function of these microorganisms invading the intestine of tilapia on the growth, development, metabolism, immunity, and overall fitness of tilapia. Moreover, we highlight the existing information on the strategies for changing the structure of the microbiota community of tilapia via diets or/and “-biotics” and recommendations for future research with the final objective of the applications of these approaches in the tilapia aquaculture industry.