Effect of Dietary Olaquindox on the Growth of Large Yellow Croaker（Pseudosciaena crocea R.） and the Distribution of Its Residues in Fish Tissues

Olaquindox（OLA）, one of quinoxaline-N, N-dioxides, has been put under ban. However it was used as a medicinal feed additive early; it promotes the growth of livestock and prevents them from dysentery and bacterial enteritis. In this study, we evaluated the effect of dietary OLA on the growth of large yellow croaker（Pseudosciaena crocea R.） and the histological distribution of OLA and its metabolite 3-methyl-quinoxaline-2-carboxylic acid（MQCA） in fish tissues. Four diets containing 0（control）, 42.5, 89.5 and 277.2 mg kg^-1 OLA, respectively, were formulated and tested, 3 cages（1.0 m × 1.0 m × 1.5 m） each diet and 100 juveniles（9.75 ± 0.35 g） each cage. The fish were fed to satiation twice a day at 05：00 am and 17：00 pm for 8 weeks. The survival rate of fish fed the diet containing 42.5 and 89.5 mg kg^-1 OLA was significantly higher than that of fish fed the diet containing 0 and 277.2 mg kg^-1 OLA（P 0.05）, while the weight gain rate of fish fed the diet containing 42.5 and 89.5 mg kg^-1 OLA was significantly higher than that of fish fed the diet without OLA（control）（P0.05）, but similar to that of fish fed the diet with 277.2 mg kg^-1 OLA. Fish fed the diet with 277.2 mg kg^-1 OLA had the highest content of OLA and MQCA in liver（3.44 and 0.39 mg kg^-1, respectively）, skin（0.46 and 0.09 mg kg^-1, respectively） and muscle（0.24 and 0.06 mg kg^-1, respectively）. In average, fish fed the diet containing OLA had the highest content of OLA and MQCA in liver which was followed by skin and muscle（P〈 0.05）, whereas OLA and MQCA were not detectable in control. Our findings demonstrated that OLA and MQCA accumulated in large yellow croaker when it was fed with the diet containing OLA, thus imposing a potential safety risk to human health.