Effects of incubation water hardness and salinity on egg hatch and fry survival of Nile tilapia Oreochromis niloticus (Linnaeus).

摘要

This study examined the effects of water hardness and salinity on yolk sac larvae and swim-up fry survival of Nile tilapia, Oreochromis niloticus (Chitralada strain), eggs during artificial incubation. Four experiments were conducted to evaluate the effects of hardness, salinity and the sources of saline incubation water. High water hardness treatments (500-4200 mg L-1 as CaCO₃) resulted in higher yolk sac larvae and swim-up fry survival than low water hardness treatments (50.0 and 132 mg L-1 as CaCO₃); although yolk sac larvae and swim-up fry survival did not differ among the high or low hardness treatments. Salinity of 4.0 g L-1 using seawater, and 4.0 and 8.0 g L-1 using unprocessed common salt resulted in the higher survival rate of yolk sac larvae and swim-up fry than other salinity treatments. Yolk sac larvae and swim-up fry survival was found to decrease with the increase in salinity and increase with the increase in water hardness. The present study demonstrated the positive effects of increased water hardness level (>132 mg L-1) on yolk sac larvae and swim-up fry survival. The study also showed that seawater salinity of 4 g L-1 was the most appropriate salinity level for incubating Nile tilapia eggs.