Swim-up fry production in the African Catfish Clarias gariepinus (Burchell) broodstocks fed with differently heated soybean-based diets

Four hundred and eighty matured yearlings of Clarias gariepinus (Burchell) (female=182±10 g; males=208±5 g) distributed into groups of 30 specimens (sex ratio 1:1) were fed differently heated soybean‐based diets. Seven approximately iso‐nitrogenous (31% crude protein) and iso‐caloric (13.97 kJ g^?1) diets were prepared from either raw soybean (SAMSOY 2, TGX 636–02D) or soybean seeds autoclaved for 5, 10, 15, 20, 25 and 30 min. The untreated and the variously heat‐treated soybean meals were mixed with other ingredients to prepare diets designated as DSoy0, DSoy5, DSoy10, DSoy15, and DSoy20, DSoy25 and DSoy30 according to the treatment time of the soybean portion of the diets, and were fed to the fish broodstocks for 84 days. The fishmeal‐based diet (DFM) served as the reference diet. The duration of heating soybean component of the experimental diet significantly (P<0.05) affected the growth performance and the number of eggs produced by the broodstocks, the percentage number of eggs fertilized and hatched as well as the survival of the progenies. The progenies of the brood fish fed diets DFM and DSoy25 with a yolk sac size of 2.78±0.6 and 2.42±0.5 mm, respectively, had significantly (P<0.05) larger yolk sacs, which were also absorbed at a significantly faster rate of 0.61±0.02 and 0.51±0.03 mm day^?1, respectively, than progenies of broodstocks fed other experimental diets. Swim‐up fry survival rates were also better in hatchlings from broodstocks fed DFM (89.5%), DSoy25 (83.8%) and Dsoy 20 (80.5%) diets than progenies from other experimental diets. This study showed that soybean meal portion processed at 116°C and 1.2 kg cm^?2 pressure for 25 min in the diet, which ensures normal reproductive function and production of healthy progenies in C. gariepinus, could serve as a substitute for fishmeal in the broodstock diets.