BACTERIAL GILL DISEASE OF FRESHWATER FISHES

Bacterial gill disease (BGD) was first described by Davis (1926, 1927), who observed it in fry and fingerling brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) in hatcheries in Vermont. The affected trout were kept in dirt-bottom ponds and were not crowded; , daily mortalities were very low. Mortalities rapidly increased when the water temperature increased and diminished when the temperature decreased. Examination of the diseased trout revealed clubbing of gill filaments. In microscopic examination of wet mounts of the filaments Davis found that the gill surface was covered with closely adhering strands of long, thin bacteria. He called the condition bacterial gill disease, but did not attempt to isolate or identify the bacteria

MYCOBACTERIOSIS (TUBERCULOSIS) OF FISHES

Mycobacteria are widely distributed in nature. They are abundant in the soil, on the surface of plants, on the skin of vertebrates, in human food (e.g., milk and butter), and in animal feeds. Most mycobacteria are saprophytic, but some species are highly pathogenic and cause diseases such as tuberculosis and leprosy in humans, and similar diseases in mammals, birds, reptiles, amphibians, and fishes. Mycobacteria that cause diseases of fishes differ considerably from those that cause diseases in humans and other mammals. Therefore, to avoid association between tuberculosis in mammals and mycobacterial infections in fishes, it is better to call the disease mycobacteriosis of fishes

COLUMNARIS DISEASE OF FISHES

Columnaris disease is a chronic to acute infection that affects salmonids and many species of warmwater fishes. The first description of the disease was given by Davis (1922) who named the disease and bacterium from the columnar arrangement of cells as seen in wet mounts. The bacterium causing columnaris disease was first isolated by Ordal and Rucker (1944). They identified the organism as belonging to the group known as slime bacteria or myxobacteria; because it produced fruiting bodies and microcysts, they named it Chondrococcus columnaris. Garnjobst (1945), who was unable to find fruiting bodies, renamed it Cytophaga columnaris. However, in the recently revised Bergey\u27s Manual of Determinative Bacteriology (Buchanan and Gibbons 1974) the columnaris organism and other fish pathogenic myxobacteria have been reclassified as flexibacteria. The forms of flexibacteria pathogenic to fish were recently reviewed by Bullock et al. (1971), McCarthy (1975), and Pacha and Ordal (1970)

FURUNCULOSIS AND OTHER DISEASES CAUSED BY \u3ci\u3eAEROMONAS SALMONICIDA\u3c/i\u3e

Aeromonas salmonicida is a gram-negative bacterium that usually produces a water-soluble brown pigment. It was first described by Emmerich and Weibel (1890) as the cause of salmonid furunculosis in Germany. Although the disease was first considered to be limited to salmonids, studies by the Furunculosis Committee (Mackie et al. 1930, 1933, 1935) showed that A. salmonicida also infected other fish species. Present indications are that A. salmonicida or its variants also produce other diseases, such as ulcerative disease of goldfish (Carassius auratus), erythrodermatitis of common carp (Cyprinus carpio), ulcer disease of trout, and systemic infections among several warmwater and marine species

PIGMENT FORMATION BY BACTERIUM SALMONICIDA

An extensive literature exists concerning the role of tyrosine and tyrosinase in the formation of melano-pigments. This interest reflects the widespread distribution of the enzyme and the conspicuousness of such pigments in man, ani-mals, and plants. Several comprehensive reviews exist on these pigments and the various factors which influence their formation (Raper, 1928; Lerner and Fitzpatrick, 1950; Dawson and Tarpley, 1951). Much of the emphasis has been directed to the metabolism of tyrosine, an amino acid which plays an important role in melano-pigmentation. The formation of these darkly colored products from their precursors is a complex phenomenon, and detailed informatio