EMBRYO-LARVAL TOXICITY OF ANTI-FUNGUS CHEMICALS USED AS PROPHYLACTIC AGENTS ON CLARIAS GARIEPINUS (BURCHELL, 1822)
Embryo-larval toxicity test of selected anti-fungus chemicals used as prophylactic agents on the African catfish (Clarias gariepinus) was conducted to assess the comparative efficacy as well as the toxicity of the different chemicals. Measured endpoints included hatching, embryo and larval survival, and larval growth. Iodine (100 mg L-1), hydrogen peroxide (250 mg L-1), malachite green (5 mg L-1) and formalin (250 mg L-1) were used as prophylactic agents. The eggs were spread on an incubating raft and continuously dipped in the treatment chemical for 15 minutes. After 48 hours, the mean hatch rate was highest in formalin-treated embryos (70%). Iodine treatment resulted in a hatch rate of 36.7%, which was slightly less than half that of the formalin treatment. Both hydrogen peroxide and malachite green resulted in 60.0% hatch rates. The results indicate that formalin-treated embryos performed significantly better than all the other chemicals. The highest percentage survival rate of 63.3% was observed in formalin at 72hph and 56.7% after 168hph. The lowest survival rate (10%) was observed in the iodine treatment group and closely followed by the group treated with malachite green (16.7%). Except for malachite green, which inhibited growth, the prophylactic treatments did not affect the growth performance of fry. This study presents evidence that can be used to support the use of formalin and hydrogen peroxide as prophylactic treatments in the early stages of C. gariepinus, although caution should be exercised due to the possibility of toxicity at higher concentrations and for longer periods of exposure.
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