All age groups may be infected with lesions manifested as small white spots

All age groups may be infected with lesions

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All age groups may be infected, with lesions, manifested as small white spots, present in the dermis, muscle, gills and internal organs. Noc. seriolae has spread from its initial focal point in Japan, and has, for example, been diagnosed among pond cultured sea bass (Lateolabrax japonicus) in Taiwan. Here, the cumulative mortality reached 17.5% within a month, with disease signs including yellow-white nodules of 0.1-0.2 cm in diameter in the gills, heart, kidney, liver and spleen (Chen et al., 2000). Rhodococcus sp. In Chinook salmon, there was evidence of melanosis and ocular oedema, leading to rupture of the cornea. There was no evidence of involvement of any internal organs (Backman et al, 1990). With Atlantic salmon, the presence of granulomas in the kidney was apparent (Claveau, 1991). Progressive low-level mortahties were recorded.
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Characteristics of the diseases 23 Rhodococcus erythropolis Freshwater- and seawater-reared Atlantic salmon, which had been previously intra- peritoneally injected with oil-adjuvanted vaccine of more than one manufacturer in Norway (five cases) and Scotland (two cases), experienced losses of 1-35%. The systemic infection centred on the peritoneal cavity, and moribund fish displayed scale loss and occasionally cutaneous haemorrhages in the abdomen and at the base of the fins. In addition, there was some evidence of abdominal distension. In Scotland, bilateral exophthalmia was reported. Internally, there were bloody ascites, spleno- megaly, peritonitis, the stomach filled with mucoidal contents, the presence of petechia, and fluid- or pus-filled cavities on the internal organs (Olsen et al, 2006a). Adhesions were present in the peritoneum, consistent with the administration of oil-adjuvanted vaccines (Olsen et ai, 2006a). Planococcaceae representative Planococcus sp. The organism has been associated with small off-white (2-4 mm diameter) round recessed spots on the heads of Atlantic salmon (Austin et ai, 1988). In large rainbow trout (average weight = 500 g), the only disease sign was the presence of watery kidney and small amounts of ascitic fluid in the peritoneal cavity (B. Austin, unpub- lished data). In addition, during 1990 the organism was associated with two popula- tions of rainbow trout fry deemed to have RTFS. These animals were anaemic, with pale gills, swollen kidney, pale liver and elongated spleen (Austin and Stobie, 1992a). Staphylococcaceae representatives Staphylococcus aureus Dead animals displayed pronounced eye disease, with the cornea becoming reddish, due to vascularisation, and then opaque. Thereafter, there was degeneration of the eye tissues, leaving a hollow cup. The brain and optic nerves were affected. In addition, diseased fish became lethargic and darker in colour (= melanosis). The internal organs did not appear to be affected (Shah and Tyagi, 1986).
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