Determination of the median lethal dose of botulinum serotype E in channel catfish fingerlings.

The median lethal dose of botulinum serotype E in 5.3-g channel catfish Ictalurus punctatus fingerlings was determined. Five tanks (five fish/tank) were assigned to each of the following treatment groups: 70, 50, 35, 25, or 15 pg of purified botulinum serotype E. Fish were injected intracoelomically and observed for 96 h. Administration of the toxin resulted in initial hyperactivity followed by erratic swimming, paresis, and death. The cumulative mortality by treatment group was 100% at 70 pg, 96% at 50 pg, 100% at 35 pg, 88% at 25 pg, and 56% at 15 pg. The median lethal dose was calculated as 13.7 pg/fish (equivalent to a 0.81 median lethal dose for mice Mus musculus) using a logistic regression model. All fish were necropsied; lesions included exophthalmia, ascites, splenic congestion, intussusception of the intestines, congested spleen, and blanching of the intestinal tract. The resultant clinical signs and lesions were similar to those noted in the syndrome of visceral toxicosis of catfish. This study indicates that channel catfish are more sensitive to the effects of botulinum serotype E than laboratory mice, and the signs and lesions of visceral toxicosis of catfish were replicated by injecting catfish with the toxin.