Influence of salinity on the developmental stages of African catfish Heterobranchus longifilis (Valenciennes, 1840)

Abstract

Salinity tolerance of fertilized eggs, yolk sac larvae, post yolk sac larvae, fingerlings and post fingerlings of Heterobranchus longifilis was investigated at 0, 1.5, 3.0, 4.5, 6.0, 7.5, 9.0, 10.5, 12.0, 13.5 and 15 parts per thousand (ppt) test salinities. The highest numerical hatchability of 75% was observed in fertilized eggs incubated in 3.0 ppt at the onset of hatching. This was however not significantly higher (p>0.05) than the 71% and 74% hatchability recorded for the control group (0 ppt) and 1.5 ppt, respectively. At the completion of hatching, the highest hatchability rate was observed in the control (0 ppt), which recorded 88% followed by 81%, 78%, 73%, 69% and 53% recorded in 1.5, 3.0, 4.5, 6.0 and 7.5 ppt, respectively. Hatching was not observed in test salinities (ppt) of 9.0, 10.5, 12.0, 13.5 and 15.0 at both onset and completion of hatching. The median lethal salinity values in 96 h (MLS-96) obtained for the post yolk sac larvae, fingerlings and post fingerling stages were 4.35, 8.00 and 8.70, respectively, demonstrating an ontogenetic variation in salinity tolerance of H. longifilis. However, salinity tolerance of the fertilized eggs, larvae, fingerlings and post fingerling of H. longifilis was generally low and typical of freshwater stenohaline species. The fingerling and post fingerling stages of H. longifilis are suitable for transfer to brackish water environment having salinity value not above 6.0 ppt for the purpose of commercial fish culture and could be a guide for the use of salt in the prophylactic and therapeutic control of pathogens sensitive to salt.