Vertebral deformities in cultured big size Rainbow Trout: Radiological analysis from juvenile to harvest size

Vertebral deformities are a big challenge in Rainbow Trout seawater aquaculture. However, supportive scientific literature is missing. The present study used radiology to follow the development of vertebral deformities in a population of farmed Rainbow Trout as they grew from 36 g to 5.5 kg. In addition, separately collected deformity screening data from three other farmed populations were included for comparison. The fish developed deformities in different vertebral regions over time, eventuating to affect almost the entire vertebral column. At this point, the fish were ~ 5.5 kg and 93 % of the fish had one or more deformed vertebrae. A negative relationship between severity of deformity (number of deformed vertebrae per individual), and fish length and weight strongly suggest a negative impact on fish welfare. The most frequently affected area was the ural region of the vertebral column. This region is a part of the caudal fin complex which also suffered from degradation of the fin rays. Ural region deformities were also frequent in the separately investigated populations. The current results indicate that Rainbow Trout are not able to maintain normal bone development under current farming conditions, consequently, jeopardizing the welfare of the fish. • There was a continuous development of vertebral deformities up to 5.5 kg harvest weight. • A larger portion of the vertebral column got affected over time. • Deformities reduce harvest weight. • Tail fin malfunction causes ural region vertebral deformities.