of layers of fibroblasts and histiocytes degenerating leucocytes with

Of layers of fibroblasts and histiocytes degenerating

This preview shows page 43 - 45 out of 594 pages.

of layers of fibroblasts and histiocytes, degenerating leucocytes with macrophages, and fibrin (Wolke, 1975). In Atlantic salmon, petechial haemorrhages have been described on the muscle lining the peritoneum (Smith, 1964). However, Ren. salmo- ninarum may be found in salmonids, e.g. charr and grayling in Alaska, without any evidence of clinical disease (Meyers et al, 1993). Renibacterial cells have been found in intra-abdominal adhesions in Atlantic salmon and coho salmon that may have previously or were considered to have received adjuvant (=adjuvanted vaccine) intraperitoneally (Bruno and Brown, 1999). Evidence suggests an impact of the disease on appetite with infected fish consuming less than their less diseased counter- parts (Pirhonen et al., 2000). Bacillaceae representatives Bacillus spp. The initial outbreak of disease led to mortahties of 10-15% of the fish in earthern ponds (Oladosu et al, 1994). Diseased fish were characterised by weakness, lethargy, emaciation and generalised necrotising dermatitis, with death occurring in a few days. Blood-tinged fluid was present in the peritoneal cavity. Petechia and focal necrosis was evident in the liver and kidney. The spleen was enlarged, soft and friable. The myocardium was described as soft and flabby. The stomach was hyperaemic (Oladosu et al., 1994). Gram-positive rods of 1-4 |im in length were observed. It should be emphasised that skin lesions revealed the presence of Aeromonas and Fla. columnare. Bacillary necrosis was described in farmed populations of catfish (Pangasius hypophthalmus) from the Mekong Delta, Vietnam. Mortalities among fish that did not otherwise respond to treatment were observed, and the disease signs centred on 1-3 mm diameter white necrotic and granulomatous areas in the kidney, liver, spleen and viscera. Apart from the presence of mostly myxosporean parasites, an organism considered as an unspeciated Bacillus was recovered (Ferguson et al, 2001).
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20 Bacterial Fish Pathogens Bacillus cereus The organism has been associated with branchionecrosis in common carp (Pychynski et al, 1981) and striped bass (Baya et al, 1992a). Bacillus mycoides An epizootic occurred in channel catfish in Alabama during 1992. The fish were darker in colour, inappetent, displayed pale areas or ulcers on the dorsal surface, focal necrosis of the epaxial muscle, and opaque muscle (Goodwin et ai, 1994). Histopathological examination revealed the presence of chains of Gram-positive rods. Bacillus subtilis The organism has been associated with branchionecrosis in common carp (Pychynski et al, 1981). Corynebacteriaceae representative Corynebacterium aquaticum The organism was associated with 3-year-old striped bass in an experimental aqua- culture facility in Maryland during December, 1990. Fish displayed pronounced bilateral exophthalmia, and contained the organism in brain tissue (Baya et ai, 1992b). Fish stopped feeding, swam more slowly and died (at this point the eyes were ruptured). Internally, the only disease sign was that the brain was haemorrhagic, and the cranium was full of blood.
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