Hormonal profile of growing male and female diploids and triploids of the blue tilapia,Oreochromis aureus,reared in intensive culture

Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower growth rate of females. When females and males are considered separately, the growth rate is not significantly different in diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and 17β-estradiol (E₂)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but the difference is not always significant. Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months compared to the triploid females and diploid males. 3,5,3′-triiodo-L-thyronine (T₃) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in 4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth rate of males may be related to the high circulating levels of T₃ and 11kT.