This study used largemouth bass (initial average weight: 33.33 ± 1.8 g) to explore the effects of adding different brown algae extracts to feed on the fish’s growth, immunity and intestinal health. Six groups were set up: a control (Group A), 0.1% sodium alginate (Group B), 0.1% oligotriosaccharide I (Group C), 0.1% oligotriosaccharide II (Group D), 0.2% brown algae powder (Group E) and 0.2% brown algae powder enzymatic product (Group F), with three replicates of 35 fish each, and a 56-day feeding experiment. Results: Compared to Group A, Groups C, D and F had a higher specific growth rate and lower feed coefficient (p < 0.05). Group D had enhanced serum SOD activity; Group F had increased antioxidant enzyme activity and decreased MDA content (p < 0.05). All experimental groups had higher serum LZM levels (p < 0.05), with no IgM difference (p > 0.05). In the intestine, treatment groups had higher α-amylase activity (p < 0.05) and no lipase difference (p > 0.05), and Groups C, D and F had higher trypsin activity (p < 0.05). Group F had the tallest villi, Group B had the thickest muscular layer (p < 0.05), and villus width was similar among groups (p > 0.05). The experimental groups had fewer intestinal pathogenic bacteria, and Group F had improved intestinal microorganism diversity and richness (p < 0.05). In conclusion, adding 0.1% oligotriosaccharide and 0.2% brown algae powder enzymatic product to feed can promote largemouth bass growth, antioxidant capacity and immunity. The 0.2% brown algae powder enzymatic product is better for intestinal development and flora improvement.

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.

To identify the optimal stocking rate of Micropterus salmoides culture in a land-based round pond recirculating aquaculture system, five stocking densities were tested, i.e., D1–D5 with 60, 70, 80, 90, and 100 fish/m², respectively. The water temperature of the experimental pond was 20.0–26.5°C. The effects of stocking density on culture productivity and physiological indexes of M. salmoides (initial body weight 50.83 ± 7.28 g) were examined. The D1 and D5 treatments exhibited significantly improved growth performance. The population weight gain in the D5 treatment was the highest, which increased by 63.73%, 52.82%, 60.93%, and 45.08%, compared with groups D1–D4 ( , each), and the feed conversion ratio was the lowest, which was decreased by 5.65%, 12.03%, 26.42%, and 21.48% compared with groups D1–D4. The levels of crude protein, essential amino acids, and total free amino acids in muscle tissue of group D3 were higher than those in the other groups. Stocking density did not differ significantly on muscle fatty acid composition , each). The activities of serum AKP and LZM and liver SOD, AKP, and LZM in group D5 were significantly higher than those in the other groups. Thus, 100 fish/m² was the optimal stocking density of M. salmoides at a size stage of 50.83∼130.13 g in the circulating water of land-based round ponds.

This experiment aimed to investigate the effects of alginate oligosaccharides on the growth performance, physiology and biochemistry, intestinal health, and liver function of Micropterus salmoides. A total of 420 Micropterus salmoides with an initial body weight of (14.07±0.69) g were randomly divided into four groups and fed with extruded diets supplemented with different concentrations of alginate oligosaccharides, namely the control group (Group C, 0% alginate oligosaccharides), Group AOS1 (0.02% alginate oligosaccharides), Group AOS2 (0.06% alginate oligosaccharides), and Group AOS3 (0.1% alginate oligosaccharides). The rearing trial lasted for 60 days. The results showed that compared with Group C, the final body weight, weight gain rate, and specific growth rate of Groups AOS1, AOS2, and AOS3 were significantly increased (P0.05). Compared with the control group, the catalase activity in all alginate oligosaccharide-supplemented groups was significantly elevated (P<0.05). In Group AOS3, the lysozyme content was significantly increased (P<0.05) and the Malondialdehyde content was significantly decreased (P<0.05). The reduced glutathione activity was significantly higher in Groups AOS2 and AOS3 than in the control group (P<0.05), and the trypsin activity in Group AOS2 was significantly enhanced (P<0.05). In addition, compared with Group C, the intestinal villus length and muscle layer thickness in Group AOS1 were significantly improved (P<0.05). Alginate oligosaccharides increased the relative abundance of beneficial bacteria and decreased the relative abundance of harmful bacteria in the intestine of Micropterus salmoides. Compared with the control group, the activities of hexokinase and phosphoenolpyruvate Carboxykinase in Groups AOS1 and AOS2 were significantly increased (P<0.05); the pyruvate kinase activity in Group AOS2 was significantly elevated; and the phosphofructokinase activity was significantly enhanced in all alginate oligosaccharide-treated groups (P<0.05). Moreover, the vacuole area ratio in all experimental groups was significantly lower than that in the control group (P<0.05), whereas the nuclear area ratio and the number of cell nuclei were significantly higher than those in the control group (P<0.05).In conclusion, alginate oligosaccharides can improve the growth performance and disease resistance, promote intestinal health, and enhance liver function of Micropterus salmoides. Based on comprehensive analysis, the optimal supplemental concentration of alginate oligosaccharides in the diet of Micropterus salmoides is 0.02%.