Vertebral column deformities in farmed rainbow trout ( Oncorhynchus mykiss )

Farmed rainbow trout (Oncorhynchus mykiss) were fed diets with either different levels of vitamin C, or diets enriched with glucan or chitin, from feeding start and 6 months onwards. At an average weight of 100 g, the trout were X-rayed to determine the deformity level. The investigations showed deformity levels from 4.8% to 12.5% among the different diet groups. Fish fed the chitin-enriched diet, the low vitamin C diet, the high vitamin C diet, and the control diet had the: highest deformity levels, ranging from 8.9% to 12.5%, while the group fed the glucan-enriched diet had the lowest level of deformities (4.8%). In all groups examined, the deformities were spread over the whole vertebral column. The deformities in the group fed the low vitamin C diet were more severe than those found in the other groups. An outbreak of the disease rainbow trout fry syndrome (RTFS) caused by the bacterium Flavobacterium psychrophilum was observed in all groups during the investigation. The findings of deformities in all examined groups indicate a possible role of F. psychrophilum in the aetiology of the observed deformities. The lower level of deformities in the group fed the glucan-enriched diet might be caused by the ability of glucan to stimulate the immune response and increase the disease resistance of fish. (C) 1999 Elsevier Science B.V. All rights reserved.