2021 Volume 56 Issue 2 Pages 79-88
Recent studies have shown efficacy of febantel (FBT) against Microsporidium seriolae in Seriola fish. This study evaluated the toxicity of FBT in Seriola quinqueradiata. Fish were gavage fed with feed containing various doses of FBT (50 to 1,000 mg/kg/day (d)) for 14 or 28 consecutive days and monitored for growth and survival. Major mortality started at 7 days in fish given 200 and 1,000 mg/kg/d FBT, while the onset of mortality in the 50 and 100 mg/kg/d groups was delayed until 15 days. Doses of 50 mg/kg/d or higher affected fish growth. Histological analyses revealed changes in the distribution and density of Nissl bodies in the brain, and a reduction of vacuolies in hepatocytes. These histological changes were rarely observed after a 9-day drug washout period, suggesting that such changes were reversible. There was no drug-related mortality in fish that received 15 mg/kg/d for 20 days or 20 mg/kg/d for 14 days. These results suggest that, although FBT can have lethal toxicity in S. quinqueradiata when administrated at doses over 50 mg/kg/d for more than 14 days or 200 mg/kg/d for more than 7 days, the drug is considered safe at the normal antiparasitic dose, including the effective dose for M. seriolae treatment (10 mg/kg/d for 5 days).
