layer of the gills and thus the inhibition of oxygen transport leading to

Layer of the gills and thus the inhibition of oxygen

This preview shows page 301 - 303 out of 594 pages.

layer of the gills, and thus the inhibition of oxygen transport leading to respiratory stress (Westfall, 1945). The practical outcome from this information is that fish- holding facilities should not be coated with copper-containing, anti-fouling com- pounds, which could trigger vibriosis. F. cholerae (non-Ol) V. cholerae survives in the aquatic environment. For example, at 25°C strain PS-7701 survived for 32 days in freshwater, saline Ringers buffer, and normal strength and diluted seawater. Survival was considerably reduced at 2°C (Yamanoi et al, 1980), an observation which coincides with the findings of Singleton et al. (1982a, b). It is Hkely that infection occurs via the water-borne route, insofar as V. cholerae appears to inhabit the aquatic environment (Lee et al., 1982; West and Lee, 1982). Vibrio fischeri, V, furnissii, V, harveyi, V, ichthyoenteri and V, logei It may be assumed that the source of the bacteria was seawater. F. ordalii V. ordalii appears to have a more restricted niche than V. harveyi and may be considered as a common water-borne organism. It has been postulated that infection (colonisation) begins in the rectum and posterior gastro-intestinal tract. Alterna- tively, its presence on skin suggests that entry may proceed by direct invasion of the integument (Ransom, 1978). F. pelagius This was not considered by Angulo et al. (1992). F. salmonicida It has been demonstrated that V. salmonicida survives for >14 months in laboratory- based experiments with seawater, when seeded at ~10^ cells/ml (Hoff, 1989). Thus, there is the potential for long-term survival in the vicinity of fish farms, as confirmed by Husevag et al. (1991). Moreover, the pathogen has been detected in the sediment (12-43 cells/ml) below fish farms, several months after an outbreak of Hitra disease. In addition, V. salmonicida has been detected in the sediments from fish farms which were not experiencing cHnical disease (Enger et al., 1989, 1991). Clearly, there will be a reservoir of the pathogen around farmed fish, from which further infections may occur.
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282 Bacterial Fish Pathogens V. splendidus It seems likely that the organism is a component of the normal, aquatic, bacterial microflora, with survival of >114 days recorded (Lopez and Angulo, 1995). F. vulnificus V. vulnificus is ubiquitous in the coastal marine and estuarine environment, where it occurs routinely in low numbers (Oliver et al., 1983), although serovar E (biotype 2) is regarded as being rare in natural waters, but extended survival occurs in sterile microcosms (Marco-Noales et al, 2004). Populations of the pathogen are almost certainly controlled by grazing and microbial antagonism (Marco-Noales et ai, 2004). However, the reservoir is almost certainly the aquatic, especially seawater, environment (H0i et ai, 1998). It has been documented to survive in brackish water and on the surfaces of eels for 14 days (Amaro et al, 1995). It is feasible that fish are constantly exposed to the potential vagaries of this organism. Moreover, it is capable of entering eels through the skin (Amaro et al, 1995).
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