with similarities to the fish pathogens were present in fresh and frozen fish

With similarities to the fish pathogens were present

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with similarities to the fish pathogens, were present in fresh and frozen fish used for yellowtail diets. This worker reported that the isolates were pathogenic, and could survive for over 6 months in the frozen state. The suggestion was made, therefore, that the contaminated diets served as an important source of infection. The impor- tance of food-borne infection was further highUghted by Taniguchi (1982a, b, 1983). It is recognised that streptococcicosis may be transmitted by contact with infected fish. In this context, Robinson and Meyer (1966) transmitted the disease by co-habiting an infected golden shiner with healthy specimens of the same species. The healthy fish succumbed to streptococcicosis, and died within 5 days. Bacteriophages of Lactococcus garvieae have been found in seawater and sedi- ment, but after defining 14 phage types (among 111 isolates), it was concluded that there was not any correlation between phage type and geographical source of the isolates (Park et ai, 1998). Work has demonstrated that Str. parauberis has the potential to survive in the marine environment in dormant, i.e. non-cultured form, after an initial culturable phase that lasted for approximately 1 and 6 months in water and sediment, respec- tively (Curras et al, 2002). The addition of nutrients to the experimental microcosms led to a return to a culturable state (Curras et al, 2002). Also, Str. parauberis has been associated with raw milk and bovine mastitis (Domenech et al, 1996). AEROBIC GRAM-POSITIVE RODS AND COCCI Renibacterium salmoninarum To date, there has been no evidence to suggest that Renibacterium is a component of the normal aquatic microflora. Indeed, in one study, water and sediment from 56 fish
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240 Bacterial Fish Pathogens farms were examined for the presence of renibacteria, but to no avail (Austin and Rayment, 1985). Twelve days after experimentally infecting Chinook salmon with a high-challenge dose, which led to infections with high numbers of renibacterial cells as determined by ELISA and FAT, the pathogen could be detected in the water (McKibben and Pascho, 1999). Survival experiments confirmed that Renibacterium could survive in fish tank sediment/faecal material for up to 21 days in the absence of any fish. However, the organism was not at any time recovered from the overlying water, suggesting that renibacteria have an affinity with organic matter. Longer survival times of 13 weeks in river, but not ground, water were reported by Hirvela-Koski (2004). The question regarding survival of the pathogen in water was the topic of detailed experimentation. This confirmed earlier work that laboratory-grown cultures were short-lived in river water. In the absence of indigen- ous water-borne organisms, i.e. using filter-sterilised river water, renibacterial cells survived for 28 days, after which there was a rapid decline in numbers. Essentially, these data show that renibacteria have the potential to survive outside of fish for limited periods, although in water it is probably unable to compete with members of the normal aquatic microflora (Austin and Rayment, 1985).
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