A possible relation between growth and number of deformed vertebrae in Atlantic salmon (Salmo salar L.)

P>The aim of the present study was to elucidate whether vertebral deformities influence on the growth performance of salmon, and if so, at what level of severity the growth performance/welfare is affected. To do this, Atlantic salmon postsmolts were individually tagged and reared in a common seacage from January 2005 until January 2006. At the end of the experiment, dissected vertebral columns were radiographed, evaluated for vertebral deformities, and the location and type of deformity was recorded. For statistical analysis the fish were grouped according to the number of deformed (d) vertebrae (v); 0 dv (n = 173), 1-5 dv (n = 43), 6-10 dv (n = 11), 11-20 dv (n = 18) and 21-44 dv (n = 31). In fish with less than six dv, the deformities were found within the tail fin region (v 50-58). Fish with 11-20 dv also had a high occurrence of dv within the tail region (V31-49), and fish with more than 20 dv also had a high occurrence of dv within the caudal trunk region (V9-30). Growth was significantly influenced by the number of dv. At the end of the experiment, fish with more than 10 dv were shorter and had a higher condition factor than normal fish, and fish with more than 20 dv were shorter, had lower weight and a higher condition factor than normal fish. In the first period in seawater (January-June) there was no detectable differences in growth (length or weight) between the groups, but the condition factor of the individuals with a high number of dv increased. In the second period (June-January), fish with more than 10 dv, had a significantly lower growth rate. This study indicate that a low occurrence of vertebral deformities have little effect on the growth performance/welfare of salmon.