Occurrence of spinal deformities in pikeperch (Sander lucioperca) early life stages in relation to size grading: a case study from a commercial hatchery

Abstract Vertebral deformities remain a significant challenge for pikeperch ( Sander lucioperca ) aquaculture. Their occurrence in fingerlings further reduces the already small number of fish suitable for grow-out, limiting pikeperch aquaculture overall. Mechanical stress has proven to influence deformation rates, and recently, the overlap of grading procedures with crucial developmental steps of spine formation has been described. In this context, this study investigates the occurrence of vertebral deformities during the times of grading in pikeperch early life stages. Sampling followed the first three manual grading steps and included sampling of different size groups resulting from the sorting steps. Using morphometric comparisons as well as morphological analyses of cleared and stained specimens, small and large groups were compared. Morphometric data confirmed the grading to result in distinct size groups; however, cannibalism could not entirely be removed. Differences between the maximum body widths and applied grid spacings suggest that mechanical pressure was exerted during sorting. The morphological examinations revealed an increase in vertebral compressions and fusions over time. Notably, transversally deformed vertebral/notochord areas were observed in the first samplings, indicating stress on the developmental precursors from an early point onwards which potentially leads to long-term effects and spine deformities. Later increases in deformation rates were timed with the progressing ossification in these stages. The gained insights from this farm example demonstrate the potential of grading procedure adaptations which can aid in reducing spinal deformation occurrences. Exemplary protocol adaptations could enhance pikeperch larviculture, improve animal welfare, and increase the economic efficiency.