Pikeperch is a species with growing value for aquaculture, but its rearing has proven to be a bottleneck for the industry (Policar et al., 2019). One factor affecting larval quality is deformations, exemplarily spinal curvatures such as lordosis and scoliosis. While many factors are known to influence the occurrence of vertebral malformations (Boglione, Gavaia, et al., 2013; Boglione, Gisbert, et al., 2013; Di Biagio et al., 2022), one factor that can be influenced by the husbandry conditions are mechanical stressors as water currency and the handling, exemplarily during size sorting procedures. The resulting deformations can negatively affect pikeperch health, welfare, and performance. Consequently, understanding the underlying mechanisms and the developmental timing of vertebral formation and the impacts of vertebral deformations in pikeperch is essential for developing effective management strategies, to improve fish welfare, and optimize aquaculture practices. This study aims to investigate the occurrence and mechanisms of vertebral column deformations in pikeperch resulting from mechanical stressors.
Materials and methods
The study involved the examination of over 1000 farmed pikeperch specimens, collected from the aquaculture pikeperch rearing facility. Hereby, the sampling focused on specimens of different age stages between 17 and 40 dph to allow observation of vertebrae formation and older postlarval specimens of 67 dph to analyse malformations that may occur. The fish were examined for the presence of lordosis using visual inspection and clearing and staining procedures (Taylor & Van Dyke, 1985). Additionally, the fluorescent properties of the Alizarin red staining were utilized to verify for the formation of vertebrae and to investigate the changes in the spinal structure.
Based on external observations, the specimen of the oldest group had a almost 65% occurrence rate of vertebral column defects. Among them, scoliotic deformations occurred at a higher rate (47.6%) than lordotic (30.5%). Caudal vertebral column deformations occurred in 26.7% of the specimens. Further analysis of the cleared and stained specimen in this age group showed that even some of the specimens with externally normal body shape possessed deformations of the vertebrae. In these cases, inconspicuous caudal vertebral column deformations were revealed by the clearing and staining procedure. This caudal spinal area proved to still be less ossified in the stages just before the onset of size sorting. In these, vertebral formations were present up to centrum 37-40 of the total 44-45 vertebrae. Fluorescence analysis indicated that influences on the vertebral deformations might be associated to the osteological developmental status of the larvae.
The observed higher incidence of caudal vertebral deformations suggests that this issue might be linked to aquaculture practices, especially size sorting procedures. Generally, sorting procedures are necessary for pikeperch rearing, because of the high growth rate during larval development (Franz et al., 2021) and the occurrence of cannibalism, especially between different sized specimens. Therefore, sorting procedures are an important tool to reduce losses in pikeperch aquaculture (Kestemont et al., 2003; Szczepkowski et al., 2011; Zakęś et al., 2004). Adjusted timing and handling protocols could effectively reduce the incidence of lordosis in farmed pikeperch in this regard. In conclusion, this study sheds light on the occurrence and impacts of vertebral column deformations in pikeperch due to mechanical impact, emphasizing the need for further research and management practices aimed at reducing the incidence of this issue in the aquaculture industry.
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