A description was given of a gram-negative, peritrichously flagellated, fermentative bacterium that was isolated on numerous occasions from kidney tissues of rainbow trout (Salmo gairdneri) afflicted with redmouth disease. Although the bacteria apparently were members of the family Enterobacteriaceae, it was impossible to determine their taxonomic position within the family with certainty. Hence it was recommended that their taxonomic position remain sub judice for the present. As a temporary designation RM bacterium was used.Redmouth disease was transmitted from infected to normal fish through the medium of water.

Cultures of the redmouth (RM) bacterium, one of the etiological agents of redmouth disease in rainbow trout (Salmo gairdneri) and certain other fishes, were characterized by means of their biochemical reactions, by deoxyribonucleic acid (DNA) hybridization, and by determination of guanine-plus-cytosine (G+C) ratios in DNA. The DNA relatedness studies confirmed the fact that the RM bacteria are members of the family Enterobacteriaceae and that they comprise a single species that is not closely related to any other species of Enterobacteriaceae. They are about 30% related to species of both Serratia and Yersinia. A comparison of the biochemical reactions of RM bacteria and serratiae indicated that there are many differences between these organisms and that biochemically the RM bacteria are most closely related to yersiniae. The G+C ratios of RM bacteria were approximated to be between 47.5 and 48.5% These values are similar to those of yersiniae but markedly different from those of serratiae. On the basis of their biochemical reactions and their G+C ratios, the RM bacteria are considered to be a new species of Yersinia, for which the name Yersinia ruckeri is proposed. Strain 2396-61 (= ATCC 29473) is designated the type strain of the species.sues of rainbow trout (Salmo gairdneri) afflicted with redmouth disease. It was concluded that the redmouth (RM) bacteria were members of the family Enterobacteriaceae, but at that time it was not possible to determine with certainty their taxonomic position within the family. In addition, Ross et al. (17) reported the results of serological studies with cultures of the RM bacterium as well as transmission of the disease from infected to normal fish through the medium of water.Redmouth disease syndrome in rainbow trout has been known for many years (18). The syndrome can be produced by certain aeromonads and pseudomonads, as well as by the bacterium reported on here (17, 18, 20). The disease is systemic, and its major gross characteristic is inflammation in the areas of the mouth and throat. It is also known as pink mouth and pink or red throat. Clinical and pathological aspects of the disease have been reviewed by others (e.g., see references 18 and 20). The disease is enzootic in some private, state, and federal hatcheries and has become epizootic on occasion. As an epizootic in hatcheries, the disease The purpose of this paper is to characterize the RM bacterium, to name and classify it properly, and to designate the type strain ofthe species. MATERIALS AND METHODSDuring the last 15 years, cultures of the RM bacterium (17) were isolated, by aseptic technique, from several hundred specimens of kidney tissue of rainbow and steelhead trout or sockeye and Chinook salmon. Most cultures were from rainbow trout. The 33 strains reported upon originated in fishes from hatcheries in Alaska, Arizona, California, Idaho, Ohio, Tennessee, and Washington (Table 1).The methods used for determining the biochemical characteristics of the above-mentioned strains were the same as those describ...

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Coho salmon (Oncorhynchus kisutch) and rainbow trout (Salmo gairdneri) were highly resistant to endotoxins from both Escherichia coli and Aeromonas salmonicida (a fish pathogen) at 14 and 18 C.This resistance was investigated with liver tryptophan pyrrolase, liver glycogen depletion in vitro, and the arterial blood pressure as indicators. Liver glycogen depletion was accelerated by both endotoxins, but there was no significant cardiovascular response or effect on liver tryptophan pyrrolase activity. Since the cardiovascular effects of histamine were also limited, it was concluded that the metabolic effects of bacterial endotoxins in salmonids are qualitatively different from those of the higher vertebrates.

In in-vitro tests on nine species of bacteria and two species of fungi, the majority of strains tested did not survive a 5-min exposure to either Betadine or Wescodyne at a concentration of 25 ppm active ingredient.

Phoma herbarum, a fungal plant saprophyte, was isolated from diseased hatchery-reared coho salmon (Oncorhynchus kisutch), chinook salmon (O. tshawytscha), and rainbow trout (Salmo gairdneri). The disease was observed at 10 national fish hatcheries in Washington and Oregon, but the low incidence of experimental infections indicate that it is only weakly contagious. Histopathological examination suggests that the air bladder is one of the primary organs infected. The visceral organs are also affected in both natural and experimental infections.

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Scolecobasidium humicola, a previously undescribed fungal pathogen of fish was isolated from coho salmon (Oncorhynchus kisutch). In natural infections the kidney was the organ most affected. The disease was difficult to transmit experimentally and appeared to be only weakly contagious.