Dichlorvos and Paraquat induced spatial avoidance response: A more realistic determinant of population decline of Oreochromis niloticus

Evelyn Tibiebi Soriwei, Hilary Chikaelo Umeokeke, Nnamdi Henry Amaeze, Olusola Ojo Ogunfeitimi, Suuru Ayomide Labinjo

Abstract


The present study evaluated the ability of Dichlorvos and Paraquat to provoke avoidance response in fingerlings of Nile tilapia Oreochromis niloticus and estimate the population immediate decline (PID). The non-forced multi-compartmented system used for non-forced assays, were constructed to allow free movement of fishes along six compartments. Fishes (n=3 per compartment/treatment, totaling 18 per system) were exposed to a gradient of Dichlorvos (1.0, 2.0, 4.0, 5.0 and 6.0 mg L-1) and Paraquat (10.0, 30.0, 50.0, 70.0, 100.0 mg L-1) and their distribution were recorded at 20 min interval for a 3-h period. Mortalities recorded in forced exposures were 17% and 0% at lowest concentrations and, 67% and 83% at highest concentrations for Dichlorvos and Paraquat correspondingly. For non-forced exposure, fishes presented a significant (p < 0.005) gradient-dependent spatial avoidance for both pesticides after 3-h. They avoided the lowest concentrations of Dichlorvos and Paraquat (1.0 and 10.0 mg L-1) by 40% and 90% respectively and 100% at the highest concentrations for both pesticides. The PID was driven by avoidance behavior rather than mortality. This result indicates that the dangers of pesticide contamination is not only in their toxicity to organisms, but also, in habitat selection processes by organism resulting in serious environmental turbulence.

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DOI: https://doi.org/10.5132/eec.2021.01.04

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