A New Disease in Cultured Yellowtail Seriola quinqueradiata Characterized by Encephalomyelitis

Abstract

In many yellowtail Seriola quinqueradiata farms in the vicinity of Uwajima city, Ehime Prefecture, Japan, a new disease has caused heavy mortalities of yearlings, mainly in summer and autumn. Symptoms included anorexia, lethargy with occasional bursts of swimming and redness in the central nervous system. In a histological survey, the most noticeable sign was severe encephalomyelitis. It is suspected that densely packed parasite-like cells (about 4 μm in diameter) in the spinal cords are the causative agent of this disease.