Contribution of research in reproductive physiology to the culture of tilapias

Abstract

In confined environments, the precocious reproductive efficiency of tilapias (various cichlid species belonging to the genera Oreochromis, Sarotherodon and Tilapia ) can rapidly lead to overcrowding and nanism. Therefore, the artificial control of reproduction in these species is very important for success in their culture. Such a control may consist either in completely preventing fry production in a population, in order to improve growth, or in favouring synchronous massive productions of alevins, in order to set up cultures with homogeneous populations.At present, some of the most intensive techniques are based on the separate rearing of male fish, either after manual sorting or following hormonal inversion treatments leading to monosex populations. New ways of obtaining a male monosex progeny are suggested, based on the viability and fertility of a new genotype YY. Recent data on the sex differentiation of tilapia gonad suggest the possible use of steroids which have been identified in vitro during the early stages of development of the testis and which exhibit high masculinizing potentialities; these studies also suggest the tentative use of specific inhibitors of the activity of some of the enzymes involved in the synthesis of the above mentioned steroids.The occurrence of parental care is an important factor in the reproductive efficiency of tilapias. Recent data show close relationships between the chronology of the mouth-brooding behaviour in Oreochromis , and that of the ovarian cycle. A better knowledge of the underlying physiological factors may facilitate the development of new techniques for the inhibition and/or the synchronization of reproduction.