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Sexual dimorphism studies in tilapias, using two pure species, Oreochormis niloticus and Sarotherodon melanotheron, and their intergeneric hybrids (O. niloticus x S. melanotheron and S. malanotheron x O. niloticus)

Toguyeni A., Fauconneau B., Mélard C., Fostier A., Lazard J., Baras E., Kühn E.R., Van Der Guyten S., Baroiller J.F.. 1997. In : Fitzsimmons K. (ed.). Proceedings of the fourth international symposium on tilapia in aquaculture = [Actes du 4ème congrès international sur tilapia en aquaculture]. s.l. : s.n., p. 200-212. International Symposium on Tilapia in Aquaculture (ISTA). 4, 1997-11-09/1997-11-12, Orlando (Etats-Unis).

This comparative study of growth performances and sexuel growth dimorphism was conducted with fish obtained from artificial reproduction. Growth was measured weekly. The levels of sexual steroids (11-KT) and thyroid hormones (T3 and T4) was measured after 74 rearing days and at the end of the experiment (103 days). Social interactions were examined with a video camera (three sequences of one hour for each group). O. niloticus and S. melanotheron achieved the best and worst growth rates, respectively, with their intergeneric hybrides standing in between. Tilapias originating from female O. niloticus (pure species and hybrid 1) exhibited a significant sexual growth dimorphism, which contrasted with the situation observed in the two other groups (originating from female S. melanotheron), where no significant difference was measured. Male tilapias from the two hybrid groups had similar growth rates, whereas hybrid females originating from female S. melanotheron (hybrid 2) grew faster than those coming from female O. niloticus (hybrid 1). The levers of 11-KT were highest in O. nioticus and lowest in S. melanotheron. The levels in the hybrid groups were similar and intermediate between those of the pure species. By contrast, the lever of T4 was highest in S. melanotheron. The levels of T3 at 74 days did not differ between groups but between sexes in all four groups. At the end of the experiment, this sex-related difference was still observed in the hybrid 2 group whilst it had vanished in the hybrid 1 group. The analysis of behavioural sequences indicated that aggressive behaviours (face to face or jaw to jaw interactions, attacks with or without poursuit) first emerged among faster growing fish (O. niloticus and hybrid 1)

Mots-clés : tilapia; oreochromis niloticus; sarotherodon; hybride; dimorphisme sexuel; gain de poids; contrôle hormonal

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