Effect Of Water Hardness On Egg Fertilization, Incubation And Hatchability Of Clarias Gariepinus And Heterobranchus Longifilis

ABSTRACT

Effect of water hardnes on egg fertilization, incubation and hatchability of virgin farm raised Clarias gariepinus and Heterobranchus longifilis was investigated. Artificial breeding was carried out by hormone inducement (Ovaprim at 0.5ml/kg fish). After latency period of 10 hours the eggs were stripped and mixed with milt from the males and incubated at 27C water temperature differently in plastic containers with incubating media prepared at various hardness of 20, 80, 160, 300mg/l CaCO; for five days. Each concentration had three replicates. Water of 8mg/l CaCO, and pH 6.9 was used as dilution water. Eggs having green dark brown colour after 10 hours of placement in water were considered to be fertilized. Hardness of 160 and 300mg/l CaCO, showed increase in fertilization success in C. gariepinus but failed to hatch successively while H. longi.filis recorded fertilization success at 20 and 80 mg/l hardness. Hatching was monitored and was considered to have commenced when 3% of the fertilized eggs had hatched. The mean hatching rate fluctuated between 8% at hardness of 300mg/l and 70% at hardness of 80mg/I in C. gariepinus and 3% at 300mg/l and of 47% at 20mg/l CaCO; in H. longifilis. The highest hatching rate of 70% was recorded at 80mg/l CaCO, in C. gariepinus while the highest hatching rate of 47% was observed at 20mg/l CaCO, in H. longifilis.