Selected egg parameters and hatching time of African catfish (Clarias gariepinus and Heterobranchus longifilis)
Egg weight, diameter and mean number per gram were determined for fertilized eggs from broodfish of Clarias gariepinus and Heterobranchus longifilis and F1, hybrid broodfish (C. gariepinus x H. longifilis). Mean egg weight was least in C. gariepinus (1.30 mg) followed by H. longifilis (1.80 mg) and highest in the F1 hybrid broodfish (2.20 mg). Egg diameter followed a similar trend 1.10-1.20mm for C. gariepinus, 1.20-1.60 mm for H. longifilis and1.50-1.90 mm for the F1 hybrid broodfish. The 3-day-old post-yolk fry measured 6.20 mm in C. gariepinus and H. longifilis but was 7.00 mm in the F2 and backcross, F1x H. longifilis. Hatching rate duration was determined for fertilized eggs that were used for the F1 cross (C. gariepinus x H. longifilis) under the harmattan period, dry season and rainy season conditions. Hatching rates ranged from 74.40-84.00% in harmattan period, 66.80-86.00% in dry season and 64.80-83.20% in the rainy season. Hatching was earliest in the dry season (18.42- 29.42h after fertilization) and occurred very late in the harmattan period (27.75-42.20h after fertilization). Dissolved oxygen concentration ranged between 4.00 mg and 5.70 mg/L in all the experimental tanks.
Keywords: Egg parameters, C. gariepinus, H. longifilis, F1 hybrid, hatching