Salinity tolerance of larvae of African catfish Clarias gariepinus (♀) X Heterobranchus bidorsalis (♂) hybrid

Abstract

Fourteen and twenty one day larvae were exposed to abrupt stepwise change in salinity (2, 4, 6, 8, 10 and 12 ppt) for 96 hours to determine mortality, median lethal mortality, MLS and median lethal time, MLT. The fourteen day-old fry that were exposed to 0 – 6 ppt recorded 90%, 87.5% 77.5% and 10% survival at the end of the 96 hours test period. Those that were subjected to 8 ppt and 10 ppt had 100% morality within 48 and 12 hours, respectively. The median lethal salinity at 96 hours (MLS-96) was 4.4 ppt which was about half the value for 6 ppt. The cumulative mortality of the graded salinities did not differ in 4 and 8 ppt but differed in 6 and 10 ppt, whereas the time intervals differed at 24 and 36 hours but did not differ at 48 – 96 hours, p<0.05. The 21 day-old fingerlings transferred into 8, 10 and 12ppt, recorded 100% mortality with 12, 3 and 2 hours, respectively. Those transferred into 0, 4 and 6 ppt had 100%, 80% and 10% survival, respectively at the end of 96hours test period. The median lethal salinity (MLS-96) for 6 and 12 hours were the same 7.19 ppt, while that for 48 hours was 4.79 ppt. The median lethal time (MLT₅₀) for 8 ppt was 8.55 hours, which was seven and half times the value for 4 ppt. The cumulative mortality the various salinity concentrations were not different in 10 and 12 ppt, but differ in 4 – 8 ppt, p<0.05. Mortality at various time intervals did not differ at 36 – 96 hours, but did at 3 and 6 hours, p<0.05.

Keywords: Catfish hybrid, Post larvae, Median lethal salinity, Median lethal time

Animal Research International (2012) 9(3): 1654 – 1664