Effects of Dietary Pyrethroid (Cypermethrin) on the Growth Performance, Cholinesterase Enzyme Activity, and Tissue Histopathology of Nile Tilapia Oreochromis niloticus

An eight-week feeding trial was conducted to investigate the effects of dietary Cypermethrin (CYP) on the growth performance, cholinesterase activities, and tissue histopathology of Nile tilapia (O. niloticus). Five experimental diets were formulated to contain 0 (CYP0), 1 (CYP1), 5 (CYP5), 25 (CYP25), and 50 (CYP50) mg CYP/100g feed diet. A total of 450 pcs of Juvenile Nile tilapia (5.35±0.47g) were randomly distributed into 15 tanks and were fed twice daily for eight weeks. Results showed that fish body weight, specific growth rate, and final total length of fish fed CYP25 and CYP50 were significantly reduced compared to CYP0, (p<0.05). The fish body weight gain in treatments CYP5, CYP25, and CYP50 were significantly lower than CYP0 (p<0.05). The most favorable fish conversion ratio were found in CYP0, CYP1, and CYP5, (p<0.05). Liver cholinesterase (AChE and BChE) activities in treatments CYP5, CYP25, and CYP50 were significantly reduced compared to CYP0, p<0.05. Necrosis, edema, mononuclear cell infiltration, villi fusion, hypertrophy, congestion, dilation of sinusoids, degeneration of nerves and fibers were evident in the sampled tissues of fish treated with CYP. This study suggests that exposure to dietary CYP of up to 50mg/100g feed diet may not significantly affect the brain cholinesterase activities of O. niloticus. However, it will significantly decrease its liver cholinesterase activities when exposed to 5mg CYP/100g feed diet. Based on broken-line regression model for body weight gain (%), the threshold toxicity level of dietary CYP in O. niloticus could be approximately 1.075mg/100g feed, over eight weeks of feeding period.