Abstract
In this study, six diets with different concentrations of nano-iron (0, 30, 60, 120, 240, 480 mg/kg) were designed to evaluate the growth, hematological parameters, antioxidant and immune status, and hypoxia tolerance of juvenile Largemouth Bass (initial weight 6.2 ± 0.2 g) through a 10-week feeding trial. The results showed that the addition of 60 mg/kg of nano-iron significantly improved the growth performance (weight gain, WG; specific growth rate, SGR), hematological parameters (red blood cell counts, RBC; hemoglobin, Hb; haematocrit, Hct; mean corpuscular volume, MCV; mean corpuscular hemoglobin, MCH), and hypoxia tolerance of juvenile Largemouth Bass (P < 0.05). Similarly, the activities of liver antioxidant enzymes (total superoxide dismutase, T-SOD; glutathione peroxidase, GPX) (P < 0.05) and the immune enzymes (acid phosphatase, ACP; alkaline phosphatase, AKP) presented increase significantly in 60 mg/kg addition group. Also, the expression levels of antioxidant (superoxide dismutase 1, SOD1; glutathione peroxidase, GPX; catalase, CAT; nuclear factor erythroid 2-related factor 2, Nrf-2), anti-inflammatory (transforming growth factor β1, TGF-β1) and anti-apoptotic (B cell lymphoma 2, Bcl-2) genes were enhanced in the 60 mg/kg group. These results indicated that supplementation of 60 mg/kg nano-iron in the diet could improve the antioxidant and immune capacity of juvenile fish. However, we observed that the addition of 480 mg/kg of nano-iron reduced the antioxidant and immune capacity of juvenile Largemouth Bass, elevated the expression of inflammatory and apoptotic genes, and exacerbated the level of oxidative stress in the organism. In conclusion, the addition of nano-iron to the diet could improve the growth performance, hematological parameters, antioxidant and immune status, and hypoxia tolerance of juvenile Largemouth Bass at an optimal concentration of 60 mg/kg.
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