Effects of dietary ethoxyquin on growth performance and body composition of large yellow croaker Pseudosciaena crocea

Ethoxyquin (6-ethoxy-2, 2, 4-trimethyl-1, 2-dihydroquinoline (EQ)) is the most common synthetic antioxidant in fish feed. However, there was little literature related to the effects of dietary EQ on growth performance of fish. The present study was conducted to investigate the effects of EQ on survival, growth, feed utilization, and body composition of large yellow croaker Pseudosciaena crocea. Five experimental diets were formulated to contain graded levels of EQ (0, 50, 150, 450 and 1350mgkg⁻¹). Each diet was randomly fed to three sea cages (1.0×1.0×1.5m), and each cage was stocked with 60 fish (with an initial body weight of 7.82±0.68g). Survival was more than 93%, and irrespective of dietary EQ levels. Specific growth rate (SGR) decreased with the increase of dietary EQ. SGR of fish fed the diet with 1350mgkg⁻¹ EQ was significantly lower than the other treatments. There were no significant differences in SGR among fish fed diets with or less than 450mgkg⁻¹ EQ. No significant difference in feed intake (FI) was found among dietary treatments. Feed efficiency ratio (FER) first increased, and then decreased with increasing dietary EQ, but no significant differences were observed among dietary treatments. No significant differences were found in moisture, protein, and ash content among dietary treatments. The lipid content, however, in fish fed the diets with EQ was higher than those fed the diet without EQ. The hepatosomatic index (HSI) and condition factor (CF) generally decreased with increasing dietary EQ level. The CF in fish fed the diet containing 1350mgkg⁻¹ EQ was significantly lower than the others. The viscerosomatic index (VSI) of fish firstly decreased with the increase of dietary EQ, the lowest value was recorded in fish fed diet with 150mgkg⁻¹ EQ, then increased with increasing dietary EQ. Results of the present study showed that EQ level in the diet of large yellow croaker should not exceed 50mgkg⁻¹.