Toxicity profile and behavioural changes in African catfish Clarias gariepinus following short-term exposure to ivermectin

Abstract

Ivermectin is one of human and veterinary medicine's most widely used antiparasitic drugs. Reports of low tolerance margins have accompanied its use in aquaculture. This study assessed the behavioural changes in African catfish - Clarias gariepinus exposed to ivermectin. Further, acute toxicity, no effect concentration, least effect concentration, and safe level of ivermectin were determined. Mortality was recorded for all the ivermectin concentrations used; this ranged from 13% to 100% for concentrations between 1.6 µgl^-1 and 24.3 µgl^-1 . There were changes in behavioural profiles of the fish especially at higher concentrations of the drug. The LC₅₀ values at 24, 48, 72 and 96 hours were 46.58 (22.45 – 450.81), 38.71 (17.69 – 648.27), 12.38 (8.19 – 24.50) and 6.53 (2.86 – 17.43) µgl^-1 respectively. The 96-hour estimated safe level of ivermectin based on the NAS/NAE method is 6.53 x 10^-1 – 6.53 x 10^-5 . Ivermectin was able to cause 100% mortality in catfish at 24.3 µgl^-1 . The low margin of safety and low toxic unit of 0.07 of the drugs make it unsuitable for use in aquaculture for the control of parasites.