Aeromonas salmonicida in Finland: pathological problems associated with atypical and typical strains

Abstract

Aeromonas salmonicida was studied at fish farms producing salmonid smolts in northern and central Finland from 1982 onwards. Aeromonas salmonicida subsp. salmonicida has been causing epizootics in salmon, Salmo salar L., and trout, S. trutta L., at two coastal farms in northern Finland sinee 1986, involving 1-29% mortality in the fish-rearing units affceted. The disease causes more serious losses of sea trout yearlings and brood fish than of salmon. The achromogenic atypical A. salmonicida proved to be the most common bacterial disease in brown and sea trout at one farm in northern Finland throughout the period, causing constant heavy losses, mainly of fingerlings, especially in 1982 -1986. It was found only occasionally in central Finland. Pigment-producing atypical A-salmonicida caused mortality among brown trout at one farm in northern Finland and one in centra! Finland.

Temperature effect on the immune defense functions of Arctic charr Salvelinus alpinus

“…Rintamäki & Valtonen (1991) have reported aAS outbreaks in Finland to occur at water temperatures higher than 15°C, which indicates an increase in the number of aAS or related Aeromonas bacteria in incoming water in July and August. However, low OD 492nm readings reflected a weak recognition of epitopes of aAS bacteria, which indicates that killed aAS cells in the vaccine were not strongly immunogenic.…”

“…Disease outbreaks are reported to occur at water temperatures above 15°C (Rintamäki & Valtonen 1991). In brackish water cultures of the Atlantic salmon Salmo salar in Iceland, aAS outbreaks take place at water temperatures around 8°C (Gudmunds7ottir 1997).…”

Characterisation of atypical Aeromonas salmonicida infection in Arctic charr Salvelinus alpinus and European grayling Thymallus thymallus

“…Bacteria have been isolated occasionally from diseased fish of various species, such as roach Rutilus rutilus, vendace Coregonus albula and dace (Madetoja et al 2003); from cyprinid fishes and the flounder Platichthys flesus in the Archipelago area of the Baltic Sea (Wiklund et al 1999); and from brown trout in the River Kymijoki and Oulujoki water basins (Rintamäki & Valtonen 1991). Isolates from these fish species were also analysed in the present study.…”

“…In salmonids the pathology is not well described. Rintamäki & Valtonen (1991) stated that the gross pathological signs of achromogenic AAS infection in salmon, brown trout and sea trout Salmo trutta m. trutta differed markedly from the signs of infection caused by either typical AS or pigment-producing AAS in the same species. Shallow lateral ulcers on the skin were typical in achromogenic AAS infection, and often no other macroscopic changes were observed.…”

“…Various types of atypical Aeromonas salmonicida (AAS) cause disease in wild and cultured fish species worldwide (Rintamäki & Valtonen 1991, Austin & Austin 1993, Gudmundsdóttir 1997, Wiklund & Dalsgaard 1998. In Finland, the infection severely affects cultured stocks of Arctic charr Salvelinus alpinus and European grayling Thymallus thymallus (hereafter referred to as charr and grayling, respectively).…”