Changes in steroid concentrations during sexual ontogenesis in tilapia

S. Rothbard, B. Moav, Z. Yaron

Research output: Contribution to journalArticlepeer-review


Testosterone, estradiol and 11-ketotestosterone were determined by radioimmunoassay in whole body extracts of tilapia at various stages of ontogenesis: before, during and after sexual differentiation. The study was conducted on Tilapia nilotica (= Oreochromis niloticus), T. mossambica (= O. mossambicus) and T. hornorum in a series of intraspecific and interspecific spawn combinations. The concentrations of testosterone and estradiol measured in homogenates prepared from groups of individuals just after fertilization were relatively high (c. 1 ng/individual) and declined to undetectable levels in 3-4-week-old fry. In older fry (4-6 weeks), the concentrations of both steroids started to increase; however, the testosterone increase was tenfold that of estradiol. In 6-8-week-old fry measured individually, the testosterone concentrations in intraspecific spawns showed a clear tendency toward two peaks of distribution. This bimodality in testosterone concentrations probably reflects the presence of males and females with different testosterone contents in the population. In interspecific crosses characterized by 100% male progeny, the distribution pattern of testosterone was unimodal, which would be expected in a monoxexual population. Estradiol and 11-ketotestosterone concentrations in the young differentiated fry at this age were low in all cases. It is suggested, therefore, that, of the steroids examined in tilapia at the age of 6-8 weeks, only testosterone reflects the processes of sex differentiation.

Original languageEnglish
Pages (from-to)59-74
Number of pages16
Issue number1
StatePublished - 1 Mar 1987


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