Abstract
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.
Highlights
The African catfish (Clarias gariepinus) is a common food fish that is farmed both within and outside of its natural range of tropical and subtropical environments
The results indicate that formalin-treated embryos performed significantly better than all the other chemicals
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, caution should be exercised due to the possibility of toxicity at higher concentrations and for longer periods of exposure
Summary
The African catfish (Clarias gariepinus) is a common food fish that is farmed both within and outside of its natural range of tropical and subtropical environments. Many farmers try to prevent disease outbreaks by using antibiotics and other chemicals as a preventative measure Several problems, such as high mortality during the incubation of eggs in hatcheries, are a result of fungal and bacterial diseases, as well as parasitic infections. Aquatic fungi (Saprolegniales) cause the most common fungal infection in fish, and infected eggs/larvae are covered in a cotton-like growth They are abundant in natural water sources used by fish hatcheries, and they often cause serious disease problems. This study was carried out to determine the comparative efficacy of these chemicals as an effective prophylactic treatment for the eggs of Clarias gariepinus and to assess the possible implications of the short-term toxicity of these prophylactic chemicals to their early stages of development
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