Effects of seawater pH on survival, growth, energy budget and oxidative stress parameters of juvenile turbot Scophthalmus maximus

This study aimed to elucidate the influence of environment pH on survival, growth, energy allocation and oxidative damage of juvenile Scophthalmus maximus (19.89±0.25 g). Six pH treatments (6.3±0.2、6.8±0.2、7.3±0.2、7.8±0.2、8.3±0.2、8.8±0.2) lasting for eight weeks were included. Measurements of survival (SR), feed conversion ratio (FCR), specific growth rate (SGR), weight gain rate (WGR), energy allocation, liver superoxide dismutase activity (SOD), catalase activity (CAT), and malondialdehyde concentration (MDA) were done. Results show that SR did not vary from pH 6.3 to 7.8, but reduced then significantly (P < 0.05); FCR raised remarkably (P < 0.05) while SGR and WGR decreased pronouncedly (P < 0.05). Most of the food energy was used in metabolism, followed by growth, feces loss and nitrogenous excretion. Energy deposited for growth showed a decreasing tendency when pH raised; while for metabolism showed a reverse trend. SOD showed insignificant difference from pH 6.3 to 7.8, but the activities then elevated obviously (P < 0.05) though a slight decrease was found from pH 8.3 to 8.8 (P > 0.05). CAT kept stable between pH 6.3 and 7.3, then sharply increased (P < 0.05), but no significant differences were found between pH 8.3 and 8.8 (P > 0.05). Subsequent decrease in MDA was found from pH 6.3 to 8.3 then the concentration smoothly increased. Overall, our results indicate that a pH in the range of 6.8 to 7.8 is recommended in the growth environment in cultivation of juvenile turbot.