Abstract:

The toxicity of organophosphate insecticides, monocrotophos and fenthion, a carbamate insecticide BPMC and a herbicide paraquat, to post-yolk fry and 3-week-old fry of Oreochromis niloticus (L.) was studied using static conditions and continuous aeration over a period of 48 hours. LT₅₀ and LC₅₀ levels were determined for all toxicants. LC50 levels for monocrotophos, paraquat, fenthion and BPMC were 16.5 ppm, 5.2 ppm, 0.6 ppm and 0.12 ppm, respectively, for post-yolk fry. Older fry were able to tolerate higher concentrations, corresponding to LC₅₀s of 45 ppm, 15 ppm, 5.2 ppm and 9 ppm for monocrotophos, paraquat, fenthion and BPMC, respectively, showing that the younger larvae were more sensitive to the toxicants and that toxicity changed with fish development. Measurements of oxygen consumption of the post-yolk fry at sublethal levels showed elevated levels to paraquat in pre-exposed fry but not under acute conditions. The sublethal levels studied showed no appreciable difference from that of the controls for the other toxicants.

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Date 1989/06/01

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