Influence of genotype and social behaviour on growth performances in tilapia Oreochromis niloticus

The first experiment of this study analysed the influence of genotype on this sexual dimorphism growth through comparison of different males genotypes: YY 100 (YY male x YY female), XY 100 (YY male x XX female), XY 50 (XY male x XX female) and XX 100 (sex reversed males). The objectives of the second experiment were to study the influence of social interactions through the use of different sex-ratios: F100, F75, F50, F25, F0 (F100 = % of females in the population). These two experiments were realised in hapas implanted in pond with "Egypt-UCS" strain of #Oreochromis niloticus#. At the end of the first experiment (140 days post-fertilisation), the genotype XY (100 or 50) present the best growth performances and genotype YY the lowest. Final body weight of sex-reversed male (XX 100) were significantly higher the XX 100 females and YY 100 males. There is no significant difference between YY 100 males and XX 50 females. According to our results, the involvement of a genetic component in sex-related growth difference between males and females is strongly suspected. We stressed upon the involvement of genes bound to the sexuel genotype (especially XY in comparison to YY and XX) independently of the sexuel phenotype. From 102 days post-fertilisation until the end of the second experiment, females of F25 population present the best growth performances. Their final body weight were significantly higher than those of all the males except F50 population males. In general, females body weight tend to increase inversely to their number in the population. Males of F50 population present better growth rate than the other males. Then, tilapia seem to be very sensitive to the effects of social interactions. These social behaviour could strongly influence the growth differences between males and females