Abstract
The present study was designed to assess the effects of fish oil with different oxidation degree on growth performance, serum biochemistry parameters and expressive abundance of oxidative stress and fat metabolism genes of orange spotted grouper Epinephelus coioides. The oxidized fish oil was conducted as follows: storage temperature: 4°C, ambient temperature (AT, [31.5 ± 3.5]°C); storage time: 45, 90, 135 days; antioxidant contents: 30 mg/kg (ethoxyquin [EQ]), 300 mg/kg Higher EQ (HEQ). According to the different treated conditions, 14 kinds of fish oil with different oxidation degree were obtained: TF+EQ [positive control (fresh oil + EQ)], TF (negative control [fresh oil]), T4°C+45d+EQ, T4°C+45d+HEQ, T4°C+90d+EQ, T4°C+90d+HEQ, T4°C+135d+EQ, T4°C+135d+HEQ, TAT+45d+EQ, TAT+45d+HEQ, TAT+90d+EQ, TAT+90d+HEQ, TAT+135d+EQ, TAT+135d+HEQ. Groupers were fed isonitrogenous and isolipidic diets containing 14 kinds of fish oil for 8 weeks, respectively. The results showed that survival, weight gain rate and thermal growth coefficient decreased as oxidation degree of dietary fish oil increased (p < 0.05). Higher serum total protein, triglyceride and glucose were observed with ascending oxidation degree of fish oil (p < 0.05). The genes expression levels of catalase, superoxide dismutase and glutathione peroxidase were up-regulated with dietary oxidized level increasing (p < 0.05). In addition, the similar status also appeared in expression of peroxisome proliferator-activated receptor gamma (PPARγ), hormone-sensitive lipase (HSL) and fatty acid synthase (FAS) genes. In conclusion, the fish oil would show negative influence on the fish health until peroxide value and p-anisidine value in oil exceed 12.96 meq/kg and 20.89. The best storage condition for fish oil is 4°C, 45 days and 30 mg/kg EQ which could keep fish oil available property to grouper.
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