Sub-Lethal Toxicity of Dichlorvos on Gills and Liver of Juvenile Heterobranchus longifilis

The study assessed the histological changes in the structure of gills and liver of juvenile Heterobranchus longifilis after exposure to varying sub-lethal concentrations of Dichlorvos. The fish, 120specimenswith mean weight of 47.33±2.31g and total length 10.67±0.58cm were selected and used for the experiment. Test fish were treated with concentrations of 0.00, 0.01, 0.015 and 0.02mg/l of Dichlorvos representing treatments T1, T2, T3 and T4 respectively. The study was carried out in a static renewal bioassay system. Fish samples were stocked in plastic bowls of 75litre capacity and the exposure period was7 days. All analyses were done using standard methods. The results showed prominent changes in the gills which included: partial epithelia lifting, hyperplasia, heavy degeneration changes, oedema, congestions and vacuolization. Changes in the liver included: congestion with sub-massive necrosis, liver parenchymal cell prominent with fatty/glycogen degeneration, hepatocytes and enlargement of portal tract. Histopathological changes on the two tissues increased with concentration of dichlorvos with severe damages observed at higher concentrations. This study showed that the use of dichlorvos as pesticides, which often find their way into the aquatic system, may have negative effects on fish. Thus, the use of organic pesticides should be encouraged. Keywords: Histopathology, sub-lethal, Heterobranchus longifilis, dichlorvos, gills and liver