Abstract
Studies were conducted to determine the effects of water hardness on egg hatchability and larval survival of aquarium fish Danio rerio. The fertilized eggs were incubated at 27 °C at six levels of water hardness: 5, 32, 63, 127, 220 and 315 mg 1-1 CaCO3. Incubation period of eggs increased with increase in water hardness. The mean hatching rate was found increased in 5 to 63 mg 1-1 hardness. However, above the hardness of 63 mg 1-1 the mean hatching rate fluctuated. The larval survival rate of 12.62% was observed in 5 mg 1-1 hardness, which showed an increasing trend with increase in water hardness level up to 63 mg 1-1 CaCO3. However, survival rate decreased with hardness level beyond 63 mg 1-1. The results showed that larval survival was significantly influenced by water hardness. Very soft water (5 to 32 mg 1-1) and very hard water (315 mg 1-1 and above) were not found suitable for larval rearing. A water hardness of 63 mg 1-1 CaCO3 was thus found to be the suitable concentration for hatching and larval survival of D. rerio.
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