<p>The objective of this study was to determine the toxicity of the neem biopesticide azadirachtin (NEEM-ON, Brand name) on the freshwater fish &lsquo;<em>Labeo rohita</em>&rsquo;. Fishes were exposed to various concentrations of botanical insecticide azadirachtin for 96 h and the percent mortality was recorded. The 96h LC₅₀ value determined by Finney&rsquo;s Probit Analysis Method was found to be 42.66 ppm. Behavioural patterns were observed critically during the whole experiment. The test fish exhibited erratic swimming, increased surfacing, decreased rate of opercular movement, reduced agility and inability to maintain normal posture and balance with increasing exposure time.</p>