Fish. Mgmt (1977), 8, No. 1. Printed in Great Britain 11 Vibriosis in Fish and its Control C. B. MUNIM (School of Environmental Sciences, Plymouth Polytechnic, Plymouth PL4 8AA}' INTRODUCTION Vibriosisis a bacterial disease of many species offish caused by members ofthe genus Vibrio. Although the taxonomy of this genus is confused, the species Vibrio anguillamm Bergman (Hendrie et ai.. 1974) is now recognized as the aetioiogical agent of many outbreaks of dis- ease among wild and famied fish. Vibriosis has been reported from a wide range of species of fish, and there appear to be no geographical limits to the disease (Anderson and Conroy, 1970). Vibriosis is principally a dis- ease of marine fish, although occasional reports of epizootics in freshwater fish occur (Evelyn, 1971; Hacking and Budd, 1971; Levin et ai., 1972). Of considerable economic importance is the common occurrence of vibriosis among commercially important species such as salmon, trout, turbot, plaice and eels reared under intensive conditions; and without proper control measures, vibriosis is likely to be one of the major disease problems to be encountered by the marine fish farmer. SYMPTOMS AND DIAGNOSIS The initial signs of infection by Vibrio are darkening of the skin, failure to feed and general inactivity. The disease is typically characterized by acute haemorrhagic septicaemia, and symptoms include congestion and haemorrhage of the skin and fins, ulcerative necrosis of the body surface, oedema, discolouration of the spleen and liver and, occasionally, exop- thahnia. The similarity of some of these symptoms to those caused by Aeromonas saimonicida had led to the description of "salt-water furunculosis" (Rucker, 1963), and accurate diagnosis is necessary. Smears taken from infected fish reveal large numbers of Gram-negative bacteria, and it may be possible to discem cell curvature. Subculture onto a suitable medium, such as tryptone-soy agar containing I per cent NaCl, followed by a few key bacteriological tests {Table I) are usually sufficient for routine diagnosis. It cannot be emphasized too strongly that isolation of vibrios from fish which have been dead for some time is of little aetioiogical significance, since vibrios are nonnal inhabitants ofthe skin and gut of marine fish (Uston, 1957; Sera and Ishida, 1972; Yoshimizu and Kimura, 1976), and post-mortem changes are very rapid. Only the isolation of V. anguiilarum from the viscera {e.g. liver or kidney) of freshly killed fish should be taken as evidence of a septicaemic in- fection with this organism, PREVENTION As with many fish diseases, much can be done to limit the occurrence and severity of vibrio- sis by careful handling of stocks and control of environmental factors. Indeed, vibriosis in farmed fish could possibly be almost wholly preventable if really good husbandry were prac- tised. •DeUvered at the 7th Annual Study Course at the University of Edinburgh on Thursday 23rd September.