Sexual dimorphism in two pure cichlid species, Oreochromis niloticus niloticus (Linnaeus 1758) and Sarotherodon melanotheron melanotheron Rüppel 1852, and their intergeneric hybrids
Growth performances and sexual growth dimorphism were compared in two pure species of tilapia, Oreochromis niloticus niloticus (OO) and Sarotherodon melanotheron melanotheron (SS), and their reciprocal intergeneric hybrids (male O. n. niloticus × female S. m. melanotheron [OS] and male S. m. melanotheron × female O. n. niloticus [SO]). Fish obtained from artificial reproduction were reared on artificial diets over 10 weeks at 25 ± 2 °C, under light regimes of 12 h light:12 h darkness. Growth was measured on a weekly basis. Social interactions were recorded with a video camera. Pure O. n. niloticus achieved the fastest growth rates (Mean Specific Growth Rate (SGR) of 2.7 ± 0.6% d–1 for males and 2.3 ± 0.4% d–1 for female) and S. m. melanotheron the slowest (1.3 ± 0.3% d–1 for males and 1.4 ± 0.3% d–1 for females). The SGR of the intergeneric hybrids fell between that of the two pure strains. OS females grew faster (1.7 ± 0.4% d–1) than SO females (1.3 ± 0.2% d–1), whereas no difference was observed between males. Aggressive behaviour emerged first among faster-growing fish (O. niloticus and SO). The role of parental components in behavioural and physiological traits of tilapia is discussed.
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