This study aimed to evaluate the median lethal concentration (LC50), acute (24 and 96 h) and sublethal (35 d) effects of deltamethrin, a synthetic pyrethroid pesticide on hormonal and enzymological responses in an Indian major carp, Labeo rohita. In this study, the LC50 values of deltamethrin for 24 and 96 h were found to be 0.438 and 0.38 mg L—1, respectively. During acute (0.438 mg L−1) and sublethal (1/10th of 24 h LC50 value, 0.0438 mg L−1) studies, plasma cortisol and prolactin levels were significantly increased (p