Vertebral column abnormalities in brown trout, Salmo trutta L

One hundred and ninety-one brown trout, Salmo trutta L., age 0/0+ to 2/2+ were collected by dipnet over nine seasons, from a farm in Hampshire, England. Seventeen were of abnormal conformation. Deformities ranged from fish slightly shortened longitudinally to fish much shortened and having a cyprinid shape. Severely affected fish had only 44 vertebrae, approximately 25% feller than normal. Adverse environmental conditions, parasitism and novel feed were discounted as causative factors. Of the five cohorts represented in the sample, one showed 25% prevalence of spinal deformity. Mean prevalence in the other four (3.25%) is comparable to that reported for wild salmon and less than that for wild and farmed rainbow trout. It is suggested that the prevalence of vertebral abnormalities in the sample of fish caught by dipnet exceeded that in the whole population at the farm because shortened fish were easier to catch than unaffected fish.