The effect of thyroxine (T4) and goitrogen on growth, liver, thyroid, and gonadal development of red tilapia (O. mossambicus × O. urolepis hornorum)

Abstract

This study provides comprehensive results on the growth, thyroid, liver, and gonadal condition, maturity, and sex ratio in red tilapia exposed to exogenous thyroxine and goitrogen. One-gram red tilapia fingerlings were reared in three groups: control, thyroxine (T4) (10 nM), and goitrogen (sodium perchlorate, 30 mg/L) for 30 days, followed by 30 days without treatment. After the first 30 days of treatment, liver enzymes and whole-body T4 and T3 were assessed. The gonadosomatic index (GSI), maturity stages and sex ratio were examined. Final body weight (FBW), weight gain (WG), specific growth rate (SGR), and survival rate were also measured. Results revealed insignificant differences among groups in FBW, WG, SGR, and GSI, but the hepatosomatic index (HSI) of the goitrogen group significantly increased. Exogenous thyroxine significantly increased whole-body T4. Liver enzymes were not affected. Thyroid follicles of the thyroxine-treated fish showed large thyroid follicles, whereas the goitrogen-treated fish showed degenerated and negligible thyroid follicles. Liver tissue of the thyroxine-treated fish group displayed a few fat vacuoles, while perchlorate-treated fish showed hydrophobic degenerated hepatocytes. At the end of 60 days, the thyroxine treatment significantly increased FBW, WG, SGR, female GSI, and male hepatosomatic index (HSI). Perchlorate and thyroxine exposure, respectively, skewed sex ratios toward males and females. Exogenous T4 enhanced the maturity stages of both females and males, while perchlorate exposure delayed their gonadal ripening. These results validated the significant role of T4 during early life of red tilapia as it could improve the growth and maturity, and affect its sex ratio, while T4 insufficiency could alter these factors.