Overlap of vertebral development and first gradings during pikeperch (Sander lucioperca) rearing: implications for possible temporal protocol adaptations

Pikeperch (Sander lucioperca) has become a species to promote diversification and technological advancement in aquaculture. However, early life rearing has proven to be a major limitation for further progress in the industry. Cannibalism related mortality is common, making regular size grading a standard preventive procedure. At the same time, spinal deformities can occur at varying and occasionally high rates. Although various factors contribute to deformation occurrences, mechanical stress appears particularly influential during the fragile early life stages. A preliminary study was carried out, to gain insights into the possible effects of first grading procedures on early development and deformation rates of pikeperch larvae and juveniles. Spine formation and ossification were found to coincide with the timing of first three grading procedures (37–60 dph). Before grading, developmental anlagen, such as the notochord in the process of sheet segmentation, as well as the forming chordacentrum-calcifications were still present. Almost completed ossification of all vertebrae centra was only observed during the last sampling (64 dph) that followed the third grading step. Further indications of an influence of the deformation rate resulted from the time of hatching and the swim bladder inflation. The results demonstrate that adjustments of the rearing protocol, specifically delaying the first grading, may help reduce spinal deformation rates. This approach could enhance fingerling quality and output quantity, and simultaneously improve animal welfare in aquaculture settings.