Transient exposures to high or low concentrations of a single or mixture of pesticides are common in aquatic organisms. Routine toxicity tests disregard transient exposures and the influence of time when examining the toxicity of contaminants. This study investigated the haematological and biochemical responses of juvenile C. gariepinus and O. niloticus to pesticide pulse exposure using three exposure patterns. The patterns include 4-hour pulse exposure to a high pesticide concentration, then 28 days of depuration, continuous exposure to a low pesticide concentration for 28 days, and 4-hour pulse exposure to a high concentration followed by continuous exposure to a low pesticide concentration for 28 days. On days 1, 14, and 28, fish samples were collected for haematological and biochemical analysis. Results showed that red blood cell count, packed cell volume, haemoglobin, platelet count, total protein, and sodium ion decreased, while white blood cell count, total cholesterol, bilirubin, urea, and potassium ion increased in both fish species after pulse, continuous and pulse & continuous exposure to the pesticides (p < 0.05). However, pulse exposure to the pesticides did not significantly affect alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase activity, and creatinine levels. The changes in these biomarkers indicate that 4-hour pulse exposure to high concentration was as hazardous as 24-hour continuous exposure to low pesticide concentration (p > 0.05). The toxic effects of pulse exposure were largely reversible by day 14. Using C. gariepinus and O. niloticus, this study shows that brief exposure to high pesticide pesticides was as hazardous as continuous pesticide exposure.
Keywords: Ecotoxicology; Fish biomarkers; Pesticide mixture; Pulse exposure; Toxicity.
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