Cold water winter lesions in Atlantic salmon

Severe ulcerative, necrotizing bacterial dermatitis, panniculitis and myositis occurred in at least 6 Atlantic salmon cage sites in New Brunswick in 1990. Mortality was due to invasion by opportunistic bacteria, or osmotic failure due to excessive ulceration. Mortality up to 10% on individual cages occurred, compared to the normal rate of 0.53% in other cages and other environments during the same 3-month period. Histological examination of lesions collected in early March, when water temperatures were 1 degrees C and food consumption was 0.2% of body wt per day, showed no evidence of healing response. Filamentous gram-negative rods were found in impression smears of all lesions, but bacteria could not be cultured, In March, in an attempt to stimulate healing, the vitamin C content of the diet was increased from 600 mg/kg of feed to 3000 mg/kg. Healing was not observed until April 30, but this also corresponded with water temperatures that rose above 4 degrees C on April 30. Other factors involved in wound repair are discussed briefly..