The effect of naphthalene on selected haematological and histopathological parameters as wellrelative growth rate in the tropical African catfish was evaluated. Healthy juvenile fish (n = 90) weighing 19.7±1.8 g were exposed to sublethal concentrations of naphthalene over a period of 35 days after which haematological and histopathological parameters were analyzed. The medianlethal concentration LC 50 of naphthalene was determined to be 6600 µg/L in Catfish withestimated safe level ranging from

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... 0.066 to 330 µg/L. Sublethal concentrations of naphthalene ledto significant declines in red blood cell (RBC) counts, haemoglobin concentration andhaematocrit. The erythrocyte indices showed mixed results with mean corpuscular haemoglobinconcentration (MCHC) showing significant elevation while changes in mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH) were not significant. Naphthalene wasimmunotoxic in exposed fish leading to significant elevations in circulating white blood cells (WBC). There was also a significant increase in platelet (PLT) count in naphthalene exposedfish. Growth rate significantly reduced in a dose response pattern. While there was no observedhistopathological alteration in the liver of exposed fish, haemorrhage with blood coagulation wasobserved in the gill sections. There were changes in the haematological parameters. Thesignificant reduction in (RBC) and the reduced growth rate of catfish shows that naphthalene isof environmental concern due to its toxicity.