Seasonal changes in sexual maturity and fecundity, and HCG-induced breeding of the catfish, Heterobranchus longifilis Val. (Clariidae), reared in Ebrie Lagoon (Ivory Coast)

Abstract

Oocyte maturation and ovulation were induced with human chorionic gonadotropin (HCG) in the African catfish, Heterobranchus longifilis. Females with a mean oocyte diameter of at least 1.1 mm were used. 100% ovulation was obtained after a single intramuscular HCG injection of between 1.0 and 2.5 I.U./g body weight; a lower dose led to high variability in individual response. Latency time depended more on temperature than on the hormone dose. Eggs could be stripped within 14 h of a dose of 1.5 I.U./g of HCG, at a temperature of 27 to 29°C. After stripping, most of the eggs were fertilized, and high percentages of normal larvae (76% ± 8) were obtained after hatching. Fish hatched in captivity and becoming sexually mature at 1 year of age (mean weight 1.5 kg) were, in turn, artificially reproduced. Seasonal changes in oocyte diameter (determined by periodic intraovarian biopsy of brooders reared in lagoon enclosures) showed a clear decrease in sexual activity at the beginning of the dry season (December) which seemed to be related to higher water temperature. However, even at that time, good quality eggs were obtained after HCG injection. Thus, eggs and fry could be produced all year round, although the mean quantity of eggs collected per female kg proved to be much less at the beginning of the dry season (26 000 ± 14 000) than during the rainy season (68 000 ± 13 000).