Influence of salinity on the
developmental stages of African catfish Heterobranchus longifilis
(Valenciennes, 1840)
H.A. Fashina-Bombata, A.N. Busari-2003
Aquaculture, 224(1-4): 213-222
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.