A comparative study on morphology, growth rate and reproduction of Clarias gariepinus (Burchell, 1822), Heterobranchus longifilis Valenciennes, 1840, and their reciprocal hybrids (Pisces, Clariidae)

A detailed study on reproduction indicated that female C. gariepinus mature earlier (5–7 months) than female H. longifilis (12–14 months). In the reciprocal hybrids, female first sexual maturity was attained at 20–21 months. Both reciprocal hybrids and parental species displayed an equilibrated sex ratio. Macroscopical and microscopical observations revealed numerous abnormalities in gonadal development of the hybrids. GSI and fecundity in female hybrids were considerably lower than those found in the parental species. Moreover, intra-ovarian tumors occurred in 20% of the hybrids. In hybrid males, GSIs were generally higher than those found in the parental species, but the spermatozoa concentration in the semen was about 100 times less. Despite these abnormalities, viable larvae, resulting from F2 and backcross fertilizations, were obtained.