Introduction
Pikeperch (Sander lucioperca) is a freshwater species of increasing interest for intensive aquaculture in Europe due to its high market value, rapid growth, and high-quality flesh (Policar et al., 2013; Pourhosein-Sarameh et al, 2024). Production is typically carried out in Recirculating Aquaculture Systems (RAS), which allow for controlled environments and shorter growth periods. However, the high operational and energy costs of RAS necessitate the maximization of production efficiency to ensure economic sustainability (Kučera et al., 2025). Stocking density is a fundamental husbandry factor that directly influences productivity, particularly during the critical juvenile on-growing phase (Kozłowski et al., 2024). While various environmental parameters such as photoperiod and temperature have been studied, specific research on optimal stocking density for pikeperch remains limited and results are often variable (Policar et al., 2019). Therefore, this study aims to evaluate the effects of different stocking densities on juvenile pikeperch reared in a RAS. The focus is placed on monitoring growth performance, blood biochemical parameters and histological morphology of liver, spleen and gills to establish efficient management protocols for this species.
Material and methods
The study was conducted over 93 days using 6.084 juvenile pikeperch randomly distributed into four groups: Control (10 kg.m-3), Low Density (LD, 30 kg.m-3), Medium Density (MD, 50 kg.m-3), and High Density (HD, 70 kg.m-3), each in triplicate tanks. Every two weeks the bimass of each tank was calculated and retired to maintain the density. Growth performance (BW, TL, SL, FC, SGR, FCR) and survival rate were evaluated biweekly, alongside a four-point scale assessment of fin condition. At the beginning (n=10) and end (n=9 per group) of the trial, biological samples were collected for multi-organ analysis. Histological examinations of the liver, spleen, and gills were performed using hematoxylin and eosin stainingon 5 µm paraffin sections to assess structural changes. All water quality parameters were maintained within optimal ranges for the species throughout the experiment.
Results and discussion
Survival was exceptionally high across all treatments (>99%), indicating that juvenile pikeperch successfully adapted to intensive RAS conditions up to 70 kg.m-3. Although high individual size variability was observed, a common trait in this species often linked to social hierarchies (Ljubobratović et al., 2016; Szkudlarek et al., 2007), standard length (SL) significantly increased in the HD group compared to the initial state (p < 0.05). Blood biochemistry revealed a significant decrease in cholesterol and amylase, alongside a downward trend in triglycerides, total protein, and albumin as density increased. These findings, combined with the transition from vacuolated to eosinophilic hepatocytes observed histologically, suggest a metabolic shift where stored energy reserves were mobilized to meet the demands of the environment (Pěnka et al., 2026). Histological adaptations in the spleen (congestion and larger MMCs) and gills (mild basal hyperplasia) represent non-pathological responses to rearing conditions. Crucially, the decrease in ALT and AST levels compared to initial values confirms the absence of liver damage (Ostolaza Perez-Cruz et al., 2026). In conclusion, stocking densities up to 70 kg.m-3 are viable for intensive pikeperch production, as the observed physiological and histological adjustments remained within a healthy adaptive range, ensuring high survival and growth performance without compromising fish welfare.
Acknowledgment
This study was supported by the Ministry of Agriculture of the Czech Republic (NAZV QL26020013).
References
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