Body malformation due to shortness of the vertebral column, in most cases of unknown cause, has been observed in fish for more than 100 yr. It periodically occurs with high prevalence in farmed Atlantic salmon Salmo salar in Norway, and this paper describes the results of macroscopic, radiographic and histologic examination of parr and seawater-transferred fish. The vertebral bodies in both age groups did not acquire the length that they normally should due to a growth disturbance leading to the condition of platyspondyly and shortness in the column. The pathologic changes became visible at different ages in both groups and the process apparently starts in intervertebral tissues. There was proliferation of connective tissue and blood vessels, and sometimes infiltration with inflammatory cells, around affected vertebrae, especially in seawater-transferred fish. This is the first description of inflammation in abnormally short-spined fish, and it may indicate an infectious etiology, at least in farmed seawater-transferred salmon.

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Atlantic salmon (Salmo salar L.) fry were reared on a fishmeal-based diet with three different levels of vitamin D 3 (0.2, 5 and 57 mg vitamin D 3 kg -1 feed, ww) from firstfeeding for 14 weeks. No significant differences were recorded in weight, length, specific growth rate, mortality, or kidney calcium concentration between the different dietary groups. No skeletal malformations or histopathological changes were recorded in any of the dietary groups. These results suggest Atlantic salmon fry to be highly tolerant of megadoses of vitamin D 3 over a limited period of time. KEY WORDS

Atlantic salmon fry were reared on a fishmeal based diet with increasing levels of vitamin A (VA) (6, 122 and 938 mg retinol kg–1 dry feed) from startfeeding and for 14 weeks. Signs of VA stress, such as reduced fat stores, liver size and growth, were found for groups receiving 122 and 938 mg retinol kg–1. Signs of vitamin A toxicity, such as increased mortality, abnormal vertebral growth, and reduced growth, were found for groups receiving 938 mg retinol kg–1. These results suggest that excess VA in the early life stages of Atlantic salmon is deleterious for normal development.

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