Effects of Water Hardness on Egg Hatchability and Larval Survival of Aquarium Fish, Danio rerio

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.