The characteristics of seven strains identified as Vibrio anguillarum, Vibrio piscium var. japonicus, or Vibrio ich thyodermis are compared with those in the original descriptions of these taxa. A proposal is made t o combine all strains as a single species, Vibrio anguillarum Bergman.The implication of vibrios as the causal organisms of diseased conditions in fish was first recognized by Bergman (4), who isolated from eels an organism which resembled the cholera vibrio and which he called Vibrio anguillarum. David ( 5 ) isolated an organism from carp and named it Vibrio piscium, using the argument that, as it was from freshwater fish, it was a different species from V. anguillarum. Subsequently, Wells and ZoBell ( 14) isolated a polarly flagellated rod from diseased marine fish, proposing the name Achromobacter ichthyodermis, a correct taxonomic assignment at that time. No reference was made by Wells and ZoBell t o the work of either Bergman or David. ZoBell and Upham (15) proposed that A . ichthyodermis should be included in the genus Pseudomonas.In 1950, Hodgkiss and Shewan (6) isolated an organism from a diseased plaice which, on comparison with the information in the 6th edition of Bergey ' s Manual o f Determinative Bacteriology, they concluded was Pseudomonas ichthyodermis. Later Shewan, Hobbs, and Hodgkiss (1 1) suggested that the organism belonged in the genus Vibrio.Other fish-pathogenic organisms belonging to the genus Vibrio have been isolated from cod by Bagge and Bagge ( l ) , who concluded that their organism was a strain of V. anguillarum; from rainbow trout by Hoshina ( 7 ) , who named his organism V. piscium var. japonicus, as it was not identical to David's original description of V. piscium; and from finnock by Smith (12), who showed that her organisms were similar to Bagge and Bagge's strain of V. anguillarum. Furthermore, Smith ( 12) suggested that the Hoshina (7) strains were nearer t o V. anguillarum than t o V. piscium.During a comprehensive study of vibrios and related organisms (2, 3) and the routine checking of cultures held in the National Collection of Marine Bacteria, it has become clear that the three species V. anguillarum, V. piscium var. japonicus, and V. ichthyodermis are phenotypically similar. No original isolates from Bergman (4), David (5), or Wells and ZoBell (14) are available, but cultures from Hodgkiss and Shewan (6), Bagge and Bagge ( l ) , Hoshina (7), and Smith (12) have all been compared. The results are given in Table 1, along with information on V. anguillarum (4), V. piscium ( 5 ) , and A . ichthyodermis (14).Bergman and David's results are not identical with those obtained for the strains held in the NCMB, but as only a very limited amount of information can be gleaned from these papers and because the methods used for certain tests, e.g., carbohydrate breakdown, are not comparable t o ours, their data are of limited value.To our knowledge, no original strains exist for V. anguillarum Bergman 1909, V. piscium David 1927, or A . ichthyodermis Wells and 64