Development and thermal tolerance of eggs in Heterobranchus longifilis, and comparison of larval developments of H-longifilis and Clarias gariepinus (Teleostei, Clariidae).

The embryonic and larval development of the African catfish Heterobranchus longifilis (Clariidae) has been described chronologically up to 17 days of age, and has been compared to that of another clariid, Clarias gariepinus. Both species show great similarities in their early development, differing merely in the ontogeny of the dorsal fin, unique and elongated in C. gariepinus, shorter and followed by a large adipose fin in H. longifilis. In H. longifilis, the termal tolerance limits of the eggs have been established: they are situated between 22 and 24 degrees C and between 34 and 35 degrees C, no hatching being observed at either 21 degrees C or 36 degrees C. Hatching rate was highest between 25 and 29 degrees C and this optimal temperature range is recommended for egg incubation in hatcheries. Incubation time varied with the temperature. Hatching took place after 26 to 33 hours and 14 to 18 hours after fertilization at temperatures of 25 and 33 degrees C respectively.