Mortality of Cultured Ayu Plecoglossus altivelis with Deep Skin Ulceration on the Thoracic Region

Abstract

An episode of mortality was observed in cultured ayu Plecoglossus altivelis with clinical signs including deep ulceration in the thoracic skin in affected fish in the Shiga Prefecture, Japan, in June, 2012. Bacteriological examination revealed that fish were infected with Flavobacterium psychrophilum, the etiologic agent of bacterial cold water disease (BCWD). Deep thoracic ulceration has not been reported in cases of BCWD in ayu. This lesion was successfully reproduced in ayu by slightly abrading the skin in the thoracic region prior to immersion challenge with F. psychrophilum. However, I could not determine the causative factor of the lesion in conventional fish farm management.