ABSTRACT

Heterobranchus longifilis juveniles weighing 22.2±0.19, lengthl6. .2 ± 0.1cm were acclimatized for seven (7) days with daily renewal of water to maintain good physicochemical quality of water suitable for the fish. Acute toxicity test of refined petroleum product (petrol) was carried out in the laboratory to determine its effect on juveniles of Heterobranchus longifilis. Different concentration were obtained through exploratory test of lml of toxicant in 9m1 of water, lml of toxicant in 99m1 of water, lml of toxicant in999m1 of water, The research was carried out using five (5) concentrations, (4.0ppm, 8.0ppm, 10.0ppm and 12.Oppm) of petrol, and a control, replicated three (3) times. Results showed behavioral changes, organ abnormalities and that petrol was toxic to the test fish even at the lowest tested concentration. Percentage mortality of 90%, 70%, 50%, 30% and 10% was recorded in 12.0ppm, 10.Oppm, 8.0ppm, 6.Oppm and 4.0ppm concentration of petrol at 96 hours exposure respectively. LC50was calculated to be 0.85ppm using probit plot analysis, while the safe concentration was calculated to be 0.7lppm. The result also showed that the mortality of Heterobranchus longifilis juveniles exposed to petrol in water increased with increase in concentration and time of exposure. DO and pH were significantly higher in control water than treated water at P<0.05, while temperature showed no significant difference between control and test samples at P<0.05. Also, the result from histopathological examination showed that lesions in the gill epithelium exposed to the different concentrations of the petrol were dose dependent with 8.Oppm12.0ppm having the highest damage which included degeneration, mucous cell proliferation, congestion with severe inflammation and calcification of the gill. The liver showed vacuolar degeneration in the hepatocytes, focal areas of necrosis and fibrosis, aggregations of inflammatory cells between the hepatocytes, dilation and congestion in blood sinusoids and thrombosis formation in the central veins, while the muscle tissues were moderately affected after the exposure. The entire test organisms in the control showed no histological abnormalities, while their staining patterns and cellular arrangement remained unaffected. The tissue was viewed under digital light microscope at the magnification of (AX100 and B X400).