Hydrogen-rich water (HRW) is widely recognized for its growth promoting, antioxidant, and anti-inflammatory properties. However, little is known about the role of HRW in aquaculture. This study aims to investigate how different concentrations of HRW affect the growth performance, digestive ability, antioxidant capacity, mTOR signaling pathway, and gut microbiota of juvenile largemouth bass. We randomly assigned 360 fish (13.73 ± 0.1 g) to three treatments. The control group was maintained in regular water, while the treatment groups were treated with different concentrations of H₂ dissolved in water, which were H1 (179.65 ± 31.95 ppb) and H2 (280.65 ± 64.43 ppb), respectively. Through an analysis of the three treatments, it was found that H1 significantly increased the final body weight, weight gain rate, specific growth rate, and survival rate, and reduced the feed conversion ratio (p < 0.05). In addition, the trypsin activity was significantly increased in the intestine (p < 0.05), and the expression of genes related to the glucose metabolism (pk and pepck) and mTOR (tor, akt, s6k1, 4ebp1, and ampka) signaling pathways were significantly increased in the liver in H1 (p < 0.05). The relative abundance of Blautia in the gut microbiota (p < 0.05) was significantly increased in H1. Therefore, these results indicated that H1 can significantly improve growth performance, promote intestinal digestion, activate the glucose metabolism pathway and mTOR signaling pathway, and increase the abundance of beneficial bacteria in the gut of largemouth bass. These findings provided valuable support for the application of HRW to support the healthy aquaculture of largemouth bass.

Grass carp are prone to excessive fat deposition in intensive aquaculture, which impairs their health and reduces economic returns. Here, we investigated the effects of replacing soybean meal with ultrafine pulverized mulberry leaves combined with multi-enzyme preparations on lipid metabolism in grass carp using phenotypic and multi-omics approaches. A total of 480 grass carp (8.45 ± 0.17 g) were fed a basal diet and two experimental diets (6% and 12%) containing mulberry leaf for 60 d. Replacing soybean meal with ultrafine pulverized mulberry leaf with multi-enzyme preparations reduced serum triglyceride, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and dorsal muscle ether extract levels, downregulated hepatic glycolysis (gk, pfk, pk) and lipogenesis (fas and acc) genes and increased intestinal lipase activity. Intestinal omics identified the lysine degradation pathway as a key pathway that regulates lipid metabolism. Reduced levels of multiple differential metabolites and enhanced microbial metabolic functions are closely associated with inhibition of lipid metabolism in grass carp. The reduction in fat deposition, particularly polyunsaturated fatty acids, the downregulation of antioxidant capacity, as indicated by decreased glutathione peroxidase and superoxide dismutase activities and reduced total antioxidant capacity, along with a decrease in malondialdehyde levels, suggests that the lipid-lowering effects could alleviate oxidative stress. Replacing soybean meal with ultrafine pulverized mulberry leaves combined with multi-enzyme preparations reduced lipid deposition and alleviated oxidative stress in grass carp by regulating the gut–liver axis. When replacing soybean meal, a 12% proportion of ultrafine pulverized mulberry leaves combined with multi-enzyme preparations in the diet is recommended.