Atypical Aeromonas salmonicida infection in naturally and experimentally infected cod, Gadus morhua L.

Abstract

Cod, Gadus morhua L., of wild origin, were reared at different temperatures for 12 months. During this period, moribund and newly dead fish were examined and samples collected for bacteriology and histopathology. Atypical Aeromonas salmonicida was isolated from 10 individuals reared at or above 7 °C. The isolates were homogeneous with respect to biochemical and antibiogram characters and similar to the ssp. achromogenes National Collection of Industrial and Marine Bacteria, UK, type strain 1110 and reference strains that have been isolated from salmonids and haddock in Iceland. Histopathological analysis of the naturally infected cod showed typical ulceration associated with atypical A. salmonicida infection and also widespread granulomatous formations. One‐year‐old cod of farmed origin, kept at 9 °C, received intraperitoneal or intramuscular injection with different doses of atypical A. salmonicida, isolated from the above wild cod. Mortalities were monitored for 28 days and the LD50 calculated. The route of bacterial injection influenced the mortality rate and LD50 value and affected, to some extent, the pathological changes observed and humoral immune parameters. Pathological changes, including haemorrhage, early stages of granuloma formation and necrotic changes, were seen in several organs. Infection appeared to induce non‐specific antibody activity against trinitrophenyl (TNP)‐haptenated protein and may have activated the complement system. Specific antibody response against atypical A. salmonicida was not detected.

Disease interaction and pathogens exchange between wild and farmed fish populations with special reference to Norway

“…Disease outbreaks seems to be stress related (Bravo, 2000;Cornick et al, 1984;Magnadottir et al, 2002).…”

Viral and bacterial diseases of Atlantic cod Gadus morhua, their prophylaxis and treatment: a review

“…Both typical and atypical Aeromonas salmonicida have been found in wild and cultured Atlantic cod (Wiklund & Dalsgaard 1998, Magnadóttir et al 2002b). The causative agent of furunculosis in Atlantic salmon A. salmonicida ssp.…”

“…Atypical strains of A. salmonicida are occasionally isolated from cod, although at present we cannot rule out the possibility that some of these infections may be secondary. Magnadóttir et al (2002b) reported isolating atypical A. salmonicida from naturally infected reared cod. The strains were homogeneous with respect to biochemical characteristics, and similar to the achromogenes sp.…”

Pathogenicity and Infection Cycle of Vibrio owensii in Larviculture of the Ornate Spiny Lobster (Panulirus ornatus)

“…A key determinant of a reliable infection model is the delivery of putative pathogens to the host using natural infection routes (38), which can significantly influence the onset and pathology of disease (26,27). In this study, vectored challenge via the aquaculture live feed organism Artemia was tested as a possible infection route, as it is a demonstrated carrier of Vibrio spp.…”