Piscicidal effect of tobacco (Nicotiana tobaccum) leaf dust on african giant catfish (Heterobranchus bidorsalis) fingerlings.

Acute toxicity of Nicotiana tubaccum leaf dust on Heterobranchus bidorsalis fingerlings (6.52±0.5g) was conducted using static bioassay tests over a period of 96 hour. The range finding test was used to determine the lethal concentration of the botanical on H. bidorsalis and was found to induce varying behavioral response in the fish. The 96 h median lethal concentration, LC50 of 0.40 g L -1 was determined graphically. A concentration dependent relationship was established for the effect of the toxicants on the test organisms. Percentage survival of the test organisms followed a regular pattern increasing with decreasing concentration. Prior to death, fish exhibited marked behavioural changes like hyperventilation, erratic swimming (vertical/spiral uncoordinated swimming movement) and settling at the bottom which revealed sensitive indicators of physiological stress in fish. Histological changes in organs (gill, liver and kidney) of H. bidorsalis fingerlings in the definitive test disclosed; congestion of blood vessel of the gill, proliferation of mucos cells, proliferation in the epithelium of the gill filament, aggregation of inflammatory cells which are related to gill function disorders. Liver shows vacuolar degeneration, diffused vacuolation in hepatocyte, inflation of the liver, vacuolation and fibrosis in the hepatocellular parenchyma and kidney shows degeneration of instertitial tissue, glomerular shrinkage, degeneration of tubular epithelia cell and severe vacuolation and lesion in kidney cell.