Effects of dietary vitamin E levels on growth, antioxidant capacity and immune response of spotted seabass (Lateolabrax maculatus) reared at different water temperatures

An 8-week growth experiment was performed to evaluate effects of dietary vitamin E (VE) levels on growth, antioxidant capacity, and immune response of spotted seabass (Lateolabrax maculatus) reared at moderate (27 °C) and high (33 °C) temperatures. Six experimental diets were formulated to contain 11.4, 32.6, 53.2, 71.4, 154.9, and 316.9 mg/kg VE, respectively. Seabass reared at 27 °C showed no significant difference in growth compared with that of seabass reared at 33 °C. However, weight gain (WG) was significantly increased as VE levels increased from 11.4 to 53.2 mg/kg and then showed no significant difference with the further increase of VE levels irrespective of water temperature. As for antioxidant capacity and immune response, irrespective of VE levels, the activity of superoxide dismutase (SOD) in the liver and gills, total antioxidant capacity (T-AOC) in the gills, and contents of complements 3 (C3) and 4 (C4) in the serum were significantly increased, while transcription of genes related to TLR-NF-κB pathway in the liver was significantly decreased in seabass reared at 27 °C compared with those of seabass reared at 33 °C. Regardless of water temperature, the activity of SOD in the liver and gills was significantly increased, while the content of malondialdehyde (MDA) in the liver was significantly decreased as dietary VE levels increased from 11.4 to 53.2 mg/kg. Regardless of water temperature, contents of complements 3 and 4 were increased as dietary VE levels increased from 11.4 to 316.9 mg/kg. At 27 °C, transcription of genes related to TLR-NF-κB pathway in the liver was significantly decreased as dietary VE levels increased from 11.4 to 53.2 mg/kg. At 33 °C, transcription of genes related to TLR-NF-κB pathway in the liver was decreased as dietary VE levels increased from 11.4 mg/kg to 71.4 mg/kg. Therefore, high temperature (33 °C) decreased the antioxidant capacity and immunity of spotted seabass compared with those of fish reared at moderate temperature (27 °C). The broken-line regression analysis of WG showed that dietary VE requirements of spotted seabass were 55.7 mg/kg of the diet at 27 °C and 48.2 mg/kg of the diet at 33 °C, then 6.55 and 6.18 mg dietary VE intake were required to gain 100 g body weight at 27 °C or 33 °C, respectively.