SUMMARY A disease of finnock (immature Salmo trutta) is described. The causal organism was found to be a Gram-negative, motile, curved rod which was also pathogenic to eels, perch, plaice and saithe. On comparison with other pathogenic vibrios from fish it was apparent that the organism was a variant of Vibrio anguillarum; the name V. anguillarum type C is suggested for it.