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Experiments were conducted to determine the effect of various incubation salinities on the hatching and survival of eggs and hatched fry respectively of the African catfish (Clarias gariepinus). The optimal salinity for the hatching of the eggs ranged from 0–5‰. Above 5‰, hatching was significantly low and no hatching occurred at 8‰ incubation salinity. Median lethal times (LT50) for fry hatched in 0, 2 and 4‰ incubation salinities, when abruptly transferred to 10‰ were 59, 49.5 and 50 h respectively. Similarly, LT50 for fry hatched in 0, 2 and 4‰ incubation salinities, and abruptly transferred to 12‰ salinity were 17, 22 and 12.50 h respectively. Increase in incubation salinity of the eggs did not seem to enhance the salinity tolerance of the hatched fry. The gradual (stepwise) increase in salinity of 1‰ per day of the catfish fry hatched in various incubation salinities (0, 1, 2, 3, 4, 5 and 6‰) had median lethal salinity values of 8, 8, 8, 10, 10, 11 and 11‰ respectively. © Rapid Science Ltd. 1998 |
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