Abstract

Deliberate or accidental contamination of ponds by widely utilized organophophorous (OP) insecticides, such as malathion is a potential problem for aquaculture in tropical countries. The aim of the study was to investigate the toxic effects of malathion (0, 0.5, 1.0, 1.50 and 2 mg L⁻¹) toxicity in the Nile tilapia (Oreochromis niloticus; 15.0  cm length and 50.0 g weight) by correlation of acute toxicity (LC₅₀) studies with biochemical and hematological parameters. Tilapia were very sensitive to malathion (96 h LC₅₀ 2ppm). The LC₅₀ for malathion (48 and 96 h) was 2.0 and 1.5 ppm, respectively. The fish shows quick response to malathion. In comparison with controls, sublethal levels of these pesticides led to a significant decrease (P<0.05) in final body weight. The erythrocyte count, haematocrit value and haemoglobin content of Nile tilapia were  Glycogen, and protein in fish muscle gradually decreased with increased pesticide concentrations. On the other hand, total production, net returns and profitability of reared fish decreased with increase in concentrations of pesticides.

Key words: Tilapia, malathion, toxicity, mortality, haemotological, biochemical.