Pseudomonas pseudoalcaligenes Pseudomonads occur in pollutedeutrophic

Pseudomonas pseudoalcaligenes pseudomonads occur in

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Pseudomonas pseudoalcaligenes Pseudomonads occur in polluted/eutrophic freshwater, which is considered to be the source of Ps. pseudoalcaligenes (Austin and Stobie, 1992b). Moreover, it was apparent that the fish farm waters received sewage from a neighbouring septic tank (B. Austin, unpublished data). Vibrionaceae representatives Vibrio alginolyticus Vibrios abound in the marine and estuarine environments (see Kaneko and Colwell, 1974), and therefore present a constant threat for any susceptible host. In particular, V. alginolyticus has been recovered from the water in marine fish tanks (Gilmour, 1977). Vibrio anguillarum Vibriosis had gained considerable notoriety in mariculture, where it has become a major limiting factor in the successful rearing of salmonids (Mahnken, 1975). To cite one example, in Denmark the disease has resulted in cumulative losses of 30% among eel populations (Bruun and Heiburg, 1935). This represents a significant economic loss. An authoritative pubHcation reported that vibriosis occurs in more than 14 countries, where it has ravaged approximately 48 species of marine fish. Vibriosis appears to have been confined initially in European waters. North America escaped the ravages of the disease until 1953 (Crosa et ai, 1977). Its arrival in Japan in 1975 may have resulted from the importation from France of contaminated eels (Muroga et ai, 1976a, b). Evidence is also accumulating that the disease may occur in fresh- water conditions (Muroga, 1975; Ghittino and Andruetto, 1977). This suggests that vibriosis is an extremely widespread problem. Consequently, the literature abounds with reports of "new" isolations and titbits of gossip, which slowly contribute to an overall saga. However, it would appear that vibriosis is, in fact, a syndrome caused by a multiplicity of vibrios (see Schiewe, 1981). Here, emphasis will be placed on V. anguillarum. The causal agent of "red-pest" in eels was first isolated by Canestrini (1893), who designated the organism as Bacterium anguillarum. A further case among eels in Sweden during 1907 was investigated by Bergman (1909), and it was directly attrib- utable to this scientist that the name of V. anguillarum was coined. V. anguillarum constitutes part of the normal microflora of the aquatic environ- ment (e.g. West and Lee, 1982; Muroga et al., 1986), particularly associated with
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280 Bacterial Fish Pathogens rotifers (Tatani et al, 1985; Muroga and Yasunobu, 1987; Mizuki et al, 2006), with maximal and minimal numbers in Summer and Winter, respectively (Larsen, 1982). Experiments have suggested that the pathogen survives for prolonged periods in seawater. Thus, Hoff (1989) reported survival for >50 months in a seawater micro- cosm. The organism may also constitute part of the normal microflora of marine fish (Oppenheimer, 1962; Mattheis, 1964). Some elegant work, albeit with only one isolate, has addressed the precise changes to the organism, i.e. starvation-stress responses, in the marine environment (Nelson et ai, 1997), where Na^ is essential for starvation-survival (Fujiwara-Nagata and Eguchi, 2004). When starved of car- bon, nitrogen and phosphorus, the number of CPUs (note: this is a dubious measure
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