Effect of water hardness on egg hatchability and larval viability of Clarias gariepinus

C.N. Molokwu, G.C. Okpokwasili-2002

Aquaculture International, 10(1): 57-64

Abstract :

Studies were conducted to determine the effect of water hardness on Clarias gariepinus egg hatchability and larval viability. The fertilized eggs were incubated at 28 °C and with water hardnesses ranging from 10–700 mg/l CaCO₃. The mean hatching rate fluctuated between 42.31% at hardness of 10 mg/l and 64.66% at 2000 mg/l. Abnormalities in the larvae were observed beyond 200 mg/l and increased with increase in water hardness. The highest larval survival of 71.05% was recorded at 60 mg/l water hardness. Based on statistics performed with analysis of variance (ANOVA) and further compared with Duncan's multiple range test (p = 0.05), the results imply that very soft water (0–10 mg/l) and very hard water (300 mg/l and above) are not suitable for Clarias egg incubation and larval rearing. A water hardness of 30–60 mg/l CaCO₃ is recommended for optimal normal hatching, high viability and maximum larval development of Clarias gariepinus.

(University of Port Harcourt, Department of Microbiology, P.M.B. 5323, Port Harcourt, Nigeria)

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