The yellow catfish (P. fulvidraco), as one of the economically-relevant freshwater fish found in China, cannot tolerate cold stress. Understanding the physiological and biochemical mechanisms under cold stress may provide insights for improving yellow catfish management in the cold. Therefore, we investigated the metabolic and intestinal microbiota changes in cold stress in response to induced cold stress. We found that cold stress in yellow catfish lead to a significant increase in the consumption of glucose and triglycerides, as well as increased use of cholesterol as an alternate energy source. Moreover, cold stress also activated several significant biological processes in the fish such as thermogenesis, oxidative phosphorylation, the spliceosome machinery, RNA transport, protein processing that occurs in the ER, and purine and pyrimidine metabolism pathways involved in energy production. On the other hand, many other mechanisms like insulin resistance, starch and sucrose metabolism, and the glyoxylate and dicarboxylate metabolic pathways that also served as energy production pathways were weakened. Furthermore, organic acids and their derivatives as well as the lipids and lipid-like molecules were mainly altered in cold stress; prenol lipids, steroids, and their derivatives were significantly upregulated, while fatty acyls and glycerophospholipids were significantly downregulated. Transcriptomic and metabolomic integrated analysis data revealed that carbohydrate metabolism, lipid metabolism, amino acid metabolism, and nucleotide metabolism were involved in cold stress resistance. In addition, the intestinal microbiota abundance was also reduce and the pathogenic bacteria of plesiomonas was rapidly appreciation, which suggesting that cold stress also impaired intestinal health. This research study could offer insights into winter management or the development of feed to promote cold resistance in yellow catfish.

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.

The study aimed to investigate the effect of hydrogen on nitrogen and phosphorus removal and microbial community composition in aquaculture water. Two groups were designed separated: Group H was charged with hydrogen and Group D was set as control. Water samples were collected at 0, 1, 2, 3, 4, 5, 6, and 7 days after hydrogen injection to detect not only the content of total nitrogen, ammonia nitrogen and phosphorus, but also microbial community composition in aquaculture water. Our findings have demonstrated that 7-days’ hydrogen treatment could effectively reduce ammonia nitrogen in aquaculture water. And in Day 7, the concentration of ammonia nitrogen in Group D was 1.66 times as that in Group H. Meanwhile, microbial structures in the water bodies of these two groups were significantly different. The abundance of bacteria such as Proteobacteria, Firmicutes, Bacteroidetes, and Desulphuria increased clearly in Group H, which means nitrification and denitrification occurred in the effect of hydrogen injection. These findings suggested that hydrogen could significantly improve aquaculture water health and reduce the production of ammonia nitrogen, which means hydrogen could be used as a functional external method to protect the aquaculture environment.

The effects of selenium supplementation in Tachysurus fulvidraco (T. fulvidraco) on low-temperature stress are not known. In this study, 280 healthy T. fulvidraco were divided into two groups, the G0 group (a control group) and the T0 group (a selenium treatment group on a 0.22 mg/kg diet), for a 6-week feeding time. Then, low-temperature stress (water temperature dropped from 26 to 13 °C, with a rate of 1 °C/h) was administered after that. The feeding results showed that selenium increased the percent weight gain (PWG), specific growth rate (SGR), and survival rate (SR) of T. fulvidraco and decreased the feed conversion rate (FCR), but these differences were not significant (p > 0.05). Under low temperatures, selenium still has no significant effects on antioxidant indexes such as glutathione peroxidase (GSH-Px) activity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content in serum (p > 0.05). However, metabolomic analysis revealed that selenium caused changes in lipids and lipid-like molles, organic acids and their derivatives, and fatty acyls. Choline, linoleic acid, and glycerophospholipid metabolism pathways; d-arginine and d-ornithine metabolism; valine, leucine, and isoleucine degradation; and biosynthesis pathways, as well as pyrimidine metabolism pathways, were activated to produce these metabolites to combat against this stress. In addition, selenium increased the diversity of intestinal microbes in T. fulvidraco and decreased the relative abundance of Plesiomonas. However, the combined analysis showed the intestinal microbe changes did not affect metabolite production. In summary, selenium activated lipid, carbohydrate, and amino acid metabolism for energy substance provision, reduced the oxidation and production of other harmful substances, and increased the intestinal microbe diversity of T. fulvidraco to improve resistance to low-temperature stress.

Intestinal health is critical for nutrient absorption and disease resistance in cultured fish. Yet, the effects of dietary Eucalyptus-derived biochar on the gut of largemouth bass (Micropterus salmoides) remain largely unexplored. This study evaluated whether supplementing diets with Eucalyptus biochar c profiles. In a 56-day feeding trial, M. salmoides were offered a standard diet containing either 0% (control) or graded levels of biochar. Juvenile fish (initial body weight 13.34 g) were randomly distributed into six groups with three replicates each (30 fish per replicate). Six extruded diets were formulated with 0, 2.5, 5.0, 10.0, 20.0, or 40.0 g kg⁻¹ of biochar, designated G0 through G5. Biochar had no significant effects on villus length, muscle layer thickness, villus width, or the activities of trypsin, amylase, and lipase, though goblet cell number was significantly higher in G5. mRNA expression of Claudin-3 and IL-10 was significantly upregulated in G1–G4, while IL-1β was significantly downregulated in G4 and G5, and TNF-α expression was reduced in G2 and G3. 16S rDNA sequencing showed increasing trends in the relative abundance of Firmicutes (43% to 49.17%) and Lactococcus (0% to 1.10%) in G3, accompanied by decreases in Proteobacteria and Klebsiella. Metabolomic analysis indicated significant upregulation of taurochenodeoxycholic acid-7-sulfate, apigenin, genistein, baicalein, taurocholic acid-3-sulfate, taurochenodeoxycholic acid-3-sulfate, and arginylmethionine in G3, whereas etoxazole and soyasaponin were significantly reduced. Dietary inclusion of 10 g kg⁻¹ Eucalyptus biochar improved intestinal health in largemouth bass by shaping the gut microbiota, promoting isoflavone biosynthesis and bile acid and amino acid metabolism, inhibiting the NF-κB pathway, and reinforcing the intestinal barrier.

Hydrogen-rich water (HRW) is known for its antioxidant, anti-inflammatory, and growth-enhancing properties. However, research on its effects on mandarin fish (Siniperca chuatsi) is limited. This study aimed to explore the effects of HRW on the growth and liver antioxidant capacity of mandarin fish. A total of 3600 fish, with an initial average weight of 30 ± 1 g, were randomly divided into four groups (three replicates each) and treated with HRW for 0 h (control), 1 h, 2 h, and 3 h over an 8-week period. In this study, we found that HRW significantly enhanced weight gain, specific growth rate, and feed intake in mandarin fish, while reducing the feed conversion ratio. It also boosted antioxidant enzyme levels (SOD and GSH-PX) in the liver and lowered MDA. Additionally, HRW increased muscle growth-related gene expression (mrf4, myos, myod, mhc) and upregulated appetite-related genes (npy and agrp) while decreasing leptin levels. This study reveals that a hydrogen concentration of 200–320 ppb, especially with a 2 h HRW treatment, produces the most significant antioxidant effects in juvenile mandarin fish, while a 3 h treatment notably enhances growth. These findings offer valuable insights and support for the advancement of the mandarin fish breeding industry.