Aspects of the reproductive biology of hatchery–reared Clarias gariepinus (Burchell 1822) in Anambra State, Nigeria II: Egg diameter

Abstract

The egg diameter distribution frequency of four batches of hatchery–reared gravid Clarias gariepinus with 10 fish per batch of varying fish weights per batch, namely: 60 ± 0.09 g, 125 ± 0.11 g, 250 ± 0.14 g and 500 ± 0.12 g was studied. Eggs from paired ovaries hardened with 1% formalin in 0.6% saline solution for 3 weeks to become non-clumping were graded through a stack of eight sieves with mesh sizes: 0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.8 mm and 2.0 mm. The different batches of similar sized eggs retained at each sieve were counted. The mean egg counts of diameters of 0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm and 1.8 mm were 402.35 ± 70.85, 682.90 ± 104.40, 65.775 ± 10.82, 364.70 ± 69.26, 1829.0 ± 378.36, 78.0750 and 18.45 ± 5.64 eggs, respectively. Of the seven (7) egg diameter frequencies (0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm and 1.8 mm) monitored, the mean egg diameter frequency of 1.2 mm showed the highest egg peak and that of 1.8 mm showed the least egg peak. There were bimodal peaks occurring at 0.5 mm and 1.2 mm in the egg distribution frequency chart indicating that C. gariepinus can spawn more than once in a breeding season.