Acute mortality event in false pilchards Harengula clupeola after salinomycin and amprolium treatment for myxozoan (Enteromyxum leei) infection.

This report documents complications in false pilchard Harengula clupeola and scad Decapterus macarellus associated with a salinomycin (60 mg kg-1) and amprolium (100 mg kg-1) gel feed treatment, along with prolonged temperature increase, for an Enteromyxum leei outbreak in a salt water, mixed species, public aquarium exhibit. Shortly after administration, a mass mortality event ensued where hundreds of false pilchards and a few scad died. Medicated gel feed was noted within the gastrointestinal tracts of all affected fish. Microscopic lesions consistently involved myodegeneration and necrosis of the gastric muscularis layer and myocardium. Salinomycin was detected in multiple tissues while amprolium was largely limited to the stomach. Based upon the clinical, pathological, and toxicologic findings, the mortality event was attributed to salinomycin toxicity. False pilchards and scad were the only species affected, suggesting a species-specific sensitivity.