Skeletal malformations in Senegalese sole (Solea senegalensis Kaup, 1858): gross morphology and radiographic correlation

Senegalese sole (Solea senegalensis) is a flatfish of increasingly interest in aquaculture in recent years. The establishment of the production requires the determination of the optimal conditions for development, growth and welfare of the sole in tanks. One important problem in cultured Senegalese sole is the presence of skeletal malformations that alter the morphology of the fish and cause the consumer's rejection. In contrast to the external study of the fish, the radiographic imaging allows to observe the existing types of deformities. The objective of this study was to define a straightforward evaluation method of skeletal alterations in Senegalese sole by means of computed radiography (CR). Fish between 255 and 352 days after hatching were randomly sampled, categorized according to their external appearance by the farm staff, and CR evaluated. Based on our previous research on skeletal malformations in Senegalese sole, we assessed the changes in the vertebrae and vertebral arches, processes and spines. Deformities varied from slight loss of structure of a single vertebra, to multiple vertebral deformities, fusions and alterations in intervertebral spaces that may result in lordosis/kyphosis or scoliosis. Anomalies in the abdominal region, caudal region and caudal complex were given a score: zero, absence of deformities; one, minor malformations; two, major malformations without altering body shape; and three, severe skeletal changes modifying gross morphology of the fish. An overall score for each fish was assumed as the highest number obtained in the three regions. The results showed that the caudal complex was the region with higher rate of deformities, usually minor; more severe malformations appeared in the caudal region. A high number of anomalies without effect on the external morphology were observed, and some gross changes in body shape did not correspond to bone alterations. CR allows the characterization of externally undetectable deformities in juvenile sole in a direct way, and is useful to discern the evolution and influence of the malformations on the gross morphology.