Toxicity of Endosulfan to the Red Hybrid Tilapia

Exposure of mature red hybrid Tilapia sp. to a range of sub-lethal concentrations of endosulfan for 21 days induced a spectrum of often not clearly distinguishable Behavioural Toxic Symptoms (BTS), ranging from reversible to eventually fatal responses. The No Observed Effect Concentration (NOEC: Below the threshold of BTS) and the Lowest Observed Effect Concentration (LOEC: Above the threshold of low intensity and reversible BTS and below the threshold of any mortality) were <0.005 and <0.0075 mg L^-1, respectively. Two other categories of BTS were also distinguishable. Medium Observed Effect Concentration (MOEC: Reversible, medium-intensity BTS in 75% and pronounced, lethal BTS in 25% individuals) and Pronounced Observed Effect Concentration (POEC: Leading to mortality of >25% to 50% of the fish) were 0.01 and 0.02 mg L^-1, respectively. The 3-day and 21-day LC₅₀ values were 0.031 and 0.016 mg L^-1, respectively.