The homeostasis of the intestinal microbiota of fish is beneficial to fish health, while food can affect the intestinal microbiota. Tilapia (Oreochromis spp.) has great economic value and is a good model to use in studying the digestion and absorption of nutrients. Furthermore, at present, due to a high demand and high price of high-quality feed raw materials, the nutritional composition of aquafeeds has been changing dynamically. There has yet to be a comprehensive review of research conducted on the influences of dietary macronutrients (proteins, lipids, and carbohydrates) on the tilapia intestinal microbiota. Therefore, this review focuses on the effects of dietary macronutrients on the gut microbiota of tilapia. Interestingly, we found that the best growth performance might not represent the best composition or functions of the gut microbiota. Overall, the unscientific addition of macronutrients to feed is harmful to the intestinal microbiota. Therefore, both growth performance and gut microbiota should be considered when evaluating certain macronutrients. It is our hope that this review will aid in regulating the intestinal microbiota of fish through nutritional means, thereby promoting tilapia farming.

An 8-week feeding trial was conducted to investigate the effects of dietary Clostridium butyricum on the growth and intestinal mucosal barrier functions of juvenile channel catfish (Ictalurus punctatus). The diets included the control group feed (CD group) and the treatment group feed (containing 1 × 10⁸ CFU/g C. butyricum; CB group). The CB group showed a rising trend in the growth performance. The CB group had significantly higher digestive and antioxidant enzyme activities, and significantly lower malondialdehyde and superoxide anion contents of the intestine. In terms of intestinal mechanical barrier, the CB group showed significantly higher gene expression of intestinal tight junction proteins. With regard to intestinal immune barrier, the CB group displayed significantly lower gene expression of pro-inflammatory factors. Regarding intestinal chemical barrier, the CB group had significantly higher gene expression of mucin-4, β-galactoside-binding lectin, lysozyme-c, and NK-lysin type 1. Dietary C. butyricum significantly increased the abundance of some beneficial bacteria and increased the levels of some beneficial metabolites in the intestine. Collectively, dietary C. butyricum could increase growth, enhance intestinal digestion and antioxidant capacity, strengthen intestinal mucosal barrier, and improve the intestinal metabolism of juvenile channel catfish.

Antioxidant and microbiota in different mucosal sites of fish play important roles. However, relevant research is lacking for rice flower carp (Procypris merus). This study investigated antioxidant and microbiota characteristics across different mucosal sites (gill, skin, and intestine) of this fish. Antioxidant analysis revealed the following: catalase activity followed gill > intestine > skin (p < 0.05); total superoxide dismutase activity showed intestine > gill > skin (p < 0.05); malondialdehyde level in the gill significantly exceeded the skin and intestine (p < 0.05); and, superoxide anion level ranked gill > intestine > skin (p < 0.05). The intestinal microbiota had the significantly lowest α-diversity (p < 0.05). Across different mucosal sites, LEfSe analysis revealed differentially abundant genera, and microbial functional prediction (BugBase) showed significant differences in Forms Biofilms, Potentially Pathogenic, Stress Tolerant, and Gram-Positive (p < 0.05). Correlation analysis between differentially abundant genera and antioxidant indicators revealed multiple significant positive correlations (p < 0.05) but no significant negative correlations (p > 0.05) in the gill; only two significant negative correlations (p < 0.05) and no significant positive correlations (p > 0.05) in the skin; and no significant correlations (p > 0.05) in the intestine. Collectively, these findings might contribute to the microecological regulation of rice flower carp.

The aquafeed industry is currently facing severe challenges such as increasingly tight supply and price fluctuations of traditional high-quality protein ingredients like fish meal and soybean meal. Therefore, actively exploring and developing new, stable, efficient, and sustainable feed protein sources to replace fish meal and soybean meal has become an urgent task and an important strategic direction for ensuring the sustainable development of the aquaculture industry. Copra meal is a widely available plant protein source with lower cost compared to fish meal and soybean meal, demonstrating good application potential. However, copra meal has disadvantages including low protein content, imbalanced amino acid profile, high crude fiber content, numerous anti-nutritional factors, and low digestibility. These issues can be addressed through certain treatments (e.g., fermentation or water soaking) to enhance its nutritional value. Currently, research on copra meal in aquafeed is still relatively scarce. To enable the broader and more effective application of this promising feed ingredient in aquafeed, this review systematically summarizes the current research progress on the nutritional characteristics, appropriate inclusion levels, processing improvement technologies, and the effects of copra meal on the growth and health of aquatic animals, aiming to provide references for promoting resource diversification and sustainable development in the aquafeed industry.

This study aimed to investigate the effects of luteolin on the growth performance and intestinal health of juvenile Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus). A total of 450 juvenile GIFT tilapia (initial body weight 8.12 ± 0.04 g) were randomly assigned to five groups (90 fish per group; three replicate tanks of 30 fish each) and fed diets containing luteolin at 0, 50, 150, 300, or 600 mg/kg (CG, LG50, LG150, LG300, and LG600, respectively) for 56 days. The results showed that with increasing luteolin supplementation, the weight gain rate (WGR) and specific growth rate (SGR) first increased and then decreased; the LG300 group had the highest WGR and SGR (significantly higher than the CG and LG600 groups, p < 0.05) and the lowest feed conversion ratio. Based on broken-line and quadratic polynomial regression analyses of the WGR and SGR, the optimal dietary luteolin supplementation level was determined to be 274.14–303.39 mg/kg. For intestinal antioxidant enzyme activities and oxidative stress, total superoxide dismutase (T-SOD) activity in the LG150 and LG300 groups was significantly higher than in the CG and LG600 groups (p < 0.05), and superoxide anion (O₂⁻) content in the LG300 group was significantly lower than in the CG, LG50, and LG600 groups (p < 0.05). Histological analysis of the intestine revealed that muscular layer thickness was significantly greater in the LG300 group than in the CG group (p < 0.05). Intestinal microbiota analysis indicated that compared with the CG group, the LG300 group showed lower relative abundances of the potential pathogens Plesiomonas and Bosea, whereas it had a higher relative abundance of the potentially beneficial bacteria Bacteroidota and Romboutsia. Intestinal untargeted metabolomics revealed that, compared with the CG group, the beneficial metabolites Chrysoeriol, Laricitrin, and Docosahexaenoylethanolamine were significantly up-regulated, whereas the biotoxins Aplysiatoxin, 17-Debromo- and Pectenotoxin 3 were significantly down-regulated in the LG300 group (p-adjust < 0.05), with the up-regulated metabolites significantly enriched in the flavone and flavonol biosynthesis pathway (p-adjust < 0.05). Collectively, dietary supplementation with an appropriate level (300 mg/kg) of luteolin can effectively improve the growth performance and intestinal health of juvenile GIFT tilapia.

To investigate the effects of Bacillus coagulans on growth performance and intestinal mucosal barrier functions of juvenile channel catfish ( Ictalurus punctatus ), this study formulated two experimental diets: a control diet (CN group, without B. coagulans ) and a B. coagulans -supplemented diet (BC group, containing 1×10 ⁸ CFU/g B. coagulans ). Each diet was assigned to three replicate tanks for an 8-week feeding trial. Compared with the CN group, the BC group exhibited a significantly lower feed conversion ratio ( P < 0.05). The BC group exhibited significantly increased activities of intestinal trypsin, α-amylase, and glutathione S-transferase ( P < 0.05), alongside significantly reduced levels of malondialdehyde and superoxide anion ( P < 0.05). Moreover, the BC group showed significantly upregulated gene expression of intestinal tight junction proteins ( zonula occludens-2 , claudin-18 , claudin-g , junctional adhesion molecule-2b , and junctional adhesion molecule-3b ; P < 0.05) and the anti-inflammatory factor ( transforming growth factor-β ; P < 0.05). Conversely, the gene expression levels of pro-inflammatory factors ( interleukin-1β , tumor necrosis factor-α , interleukin-6 , and interferon-γ1 ) were significantly downregulated ( P < 0.05). Additionally, genes associated with the intestinal chemical barrier ( mucin-4 , lysozyme-c , lysozyme-g , NK-lysin type 1 , and β-defensin ) were significantly upregulated ( P < 0.05). Intestinal microbiota analysis revealed increased relative abundance of beneficial bacteria (e.g., Firmicutes, Bacilli, Erysipelotrichales, and Turicibacter ) in the BC group ( P < 0.05). Non-targeted metabolomics further indicated significantly elevated levels of beneficial metabolites, including soyasaponin I and taurine in the BC group ( P < 0.05). In summary, dietary B. coagulans improved feed utilization, enhanced intestinal digestive and antioxidant capacity, strengthened mucosal barrier functions, optimized intestinal metabolism, and promoted intestinal health.