The present study aimed to investigate the influence of guar gum supplementation in high-fat diets on the growth performance and intestinal oxidative stress, inflammation, and apoptosis of juvenile largemouth bass. Five isonitrogenous diets were prepared: a control diet (10% crude lipid, C), a high-fat diet (17% crude lipid, HF), and three high-fat diets supplemented with 0.3% guar gum (GG0.3), 1% guar gum (GG1), and 3% guar gum (GG3). Largemouth bass (3.1±0.2 g) were randomly assigned to fifteen tanks (30 fish/tank) and fed for 8 weeks. The results demonstrated that GG0.3 significantly increased specific growth rate (SGR) and increased feed conversion ratio (FCR) compared to HF (P < 0.05). For histology, high-fat diets containing guar gum significantly increased intestinal villus length, villus width, and perimeter ratio, compared with HF (P < 0.05). Compared with Control, HF significantly decreased reduced glutathione (GSH) contents and increased malondialdehyde (MDA) contents in the intestine (P < 0.05). Additionally, HF significantly increased the expression of interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), and cysteine-aspartic proteases 9 (Caspase 9) in the intestine (P < 0.05). Compared to HF, GG0.3 significantly decreased MDA contents, increased GSH contents, and downregulated the expression of IL-1β, TNF-α, and Caspase 3 than diet HF in the intestine (P < 0.05). These results suggest that guar gum can alleviate the adverse effects of high-fat diets on growth and gut health in fish.

Aquaculture intensification has resulted in serious disease outbreaks in largemouth bass production. Compounds containing copper (Cu) are widely used as therapeutic agents in aquaculture. Currently, Cu misuse has been a severe issue in largemouth bass farming. However, few investigations have been performed on Cu toxicity in largemouth bass so far. In this study, an acute and a chronic toxicity test was carried out to determine the toxicity and the recommended dose of waterborne Cu in largemouth bass. In the acute toxicity bioassay, fish (2.58 ± 0.03 g) were exposed to 0 (control), 3, 6, 9, 18, or 30 mg/L Cu, and the results showed that the 96-h LC ₅₀ of waterborne Cu was 12.78 mg/L. Then a 30-day chronic toxicity test containing six treatments (i.e., 0, 51.3, 164, 513, 1640, and 5130 μg/L Cu) was conducted to investigate the influence of Cu on intestinal and renal health in terms of oxidative stress in juvenile largemouth bass (2.69 ± 0.02 g). The results showed that Cu concentrations at and above 51.3 μg/L significantly increased the malondialdehyde contents (in the intestine) and simultaneously decreased total superoxide dismutase activity levels (in the intestine and kidney), glutathione peroxidase activity levels (in the kidney), and reduced glutathione contents (in the kidney), compared to control. In contrast to control, fish exposed to high Cu concentrations (at and above 1640 μg/L) demonstrated lower catalase activity levels in the intestine and kidney. Based on the findings in the study, waterborne Cu content for largemouth bass farming was recommended to be less than 51.3 μg/L.