V ordalii Essentially the disease may be categorised as a haemorrhagic

V ordalii essentially the disease may be categorised

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V. ordalii Essentially, the disease may be categorised as a haemorrhagic septicaemia. However, there are subtle differences in the pathologies of the diseases caused by V. anguillarum and V. ordalii. In the case of V. ordalii in Pacific salmon, there is a tendency for the formation of micro-colonies in the skeletal and heart muscle, gill tissue, and in both the anterior and posterior regions of the gastro-intestinal tract (Ransom, 1978; Ransom et aL, 1984). Moreover, bacteraemia developed much later in the disease cycle than with V. anguillarum. Perhaps, this accounted for the lower numbers of bacterial cells in the blood. A further difference concerned the marked decrease in the numbers of leucocytes in the blood, i.e. leucopenia (Ransom, 1978; Harbell et aL, 1979; Ransom et aL, 1984). V, pelagius An epizootic of juvenile farmed turbot in northwest Spain occurred during January and February 1991 when the water temperature was 12-15°C, with fish displaying eroded dorsal fins and tail, haemorrhages at the base of the fins, haemorrhages on the internal organs and intestines full of mucus Hquid (Angulo et aL, 1992). The total losses amounted to 3% of the turbot population. Subsequently, larval turbot were described with swollen and necrotic secondary gill lamellae, sloughing off of the
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44 Bacterial Fish Pathogens intestinal mucosa and necrosis of the haematopoietic tissues of the kidney (Villamil et aL, 2003). V. salmonicida With the tremendous increases in production of Atlantic salmon in Norway, it was perhaps inevitable that at some time a new or emerging disease would cause havoc to the industry. Thus, in 1979 such a "new" disease appeared in salmon farms located around the island of Hitra, south of Trondheim in Norway. In 1983, the disease appeared in Stavanger and, in particular, the large number offish farms in the Bergen region. The disease, coined coldwater vibriosis or Hitra disease (Egidius et al, 1981), occurs mainly during the period of late Autumn to early Spring. The disease is now widespread throughout Norway, and there are some reports of outbreaks in Scot- land, Shetland (Bruno et ai, 1985) and Canada. The disease resembles a generalised haemorrhagic septicaemia. Externally, haemorrhaging may be evident around the abdomen (Holm et al, 1985). Internally, there is often evidence of anaemia, haemorrhaging on the organs, swim bladder, abdominal wall and posterior gastro- intestinal tract (Poppe et ai, 1985; Holm et ai, 1985; Egidius et ai, 1986). V. splendidus During 1987, a disease occurred in cultured turbot in northwest Spain. During the outbreak, there was a continuous low-level mortahty amounting to 4% of the total stock. Infected fish contained a virus, deemed to be a reovirus, and a bacterium, which was considered to resemble V. splendidus (Lupiani et ai, 1989). Interestingly, a similar organism has been recovered from diseased Atlantic salmon in Scotland (B. Austin, unpubHshed data), turbot (including larval turbot in Spain; Thomson et al, 2005), sea bass in Norway (Myhr et al, 1991) and gilthead sea bream in Spain (Balebona et al, 1998). Diseased turbot displayed swollen abdomen and haemorrhaging in the mouth, at the anus and base of the fins. The swimming be-
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