Inter-individual variability in reproductive success and somatic growth in Cichlasoma dimerus (Heckel, 1840)

Environmental factors and social interactions are known to affect somatic growth and reproduction in teleost fish. It has been described for Cichlasoma dimerus that only one pair is formed under a wide range of laboratory conditions. However, this was not observed in tanks composed of three males and three females, where multiple pair formation occurred. Thus, our objective was to evaluate somatic growth and reproductive performance in C. dimerus under this particular condition, in which more than one pair is expected to be formed. A clear sexual growth dimorphism, with males growing faster than females, and multiple pair formation, sometimes simultaneously, were observed. Both features were absent in previous studies with other aquaria structures. Additionally, there was a significant association between reproductive events and body size, where the bigger the fish, both male and female, the higher the number of reproductive events. Despite the sexual growth dimorphism, no differences were observed between males and females in IGF-I and GHR2 mRNA levels. The results obtained for this social species show a high inter-individual variability in the aquaria in regard to reproductive success and growth. This may have implications on experimental design, where a low level of heterogeneity between fish is desirable. If this variability is not taken into account, possible treatment effects may not be detected.