THE PATHOGEN OF RED-HEAD DISEASE IN EUROPEAN EEL(ANGUILLA ANGUILLA)

During the cultivation of European eel (Anguilla anguilla), a seriousepizootic occurred among cultured elvers in southern provinces of China The diseasewas called red-head disease, because one of the typical symptoms was reddening onthe head, which was caused by subcutaneous haemorrhaging. The present paperdescribed characteristics of the red-head disease. Three strains of bacteria wereisolated from the blood of the spontaneously diseased eels. After intramuscular orfeeding inoculation with the bacterial suspension, the healthy eels appeared thesymptoms similar to those in natural diseased eels. The mortality of injection andfeeding challenge trials were 83% and 67%, respectively. Another strain of the samepathogen was isolated from the artificially infected eel. Characteristics of four strainswere completely consistent.The orgenisms were gram-negative, short rod, motile bymeans of peritrichous flagella, facultatively anaerobic. Glucose was catabolized withthe production of acid. Oxidase, Voges-Proskauer reaction, Simmon's citrate, β-galactosidase and phenylalanine deaminase were negative. Catalase, indole, hydrogensulfide and methyl red test were positive.Nitrate was reduced. Lysine and ornithinedecarboxylase were produced. The isolates produced acid from galactose, glycerol,levulose, maltose and mannose, but not from arabinose, cellobiose, inositol, lactose,mannitol, a-methyl-D-glucoside, raffinose, rhamnose, salicin. sorbitol, sucrose andxylose. Physiological and biochemical characteristics of the present isolates were thesame as those of Edwardsiella tarda described in the Bergey's Manual ofDeterminative Bacteriology 9th ed. (Holt et al., 1994), except that the isolates did notproduce gas from glucose. Therefore, the pathogen isolated from the diseasedEuropean eels was identified as Edwardsiella tarda.