Introduction
Pikeperch (Sander lucioperca) is a species of growing importance in European aquaculture due to its high market value (Policar et al., 2019) and suitability for intensive production systems. The In-Pond Raceway System (IPRS) represents a promising semi-intensive approach combining advantages of pond culture and controlled rearing conditions (Nagy et al., 2022, Ku��era et al., 2025). However to be able to further incorporate the IPRS in European inland aquaculture practices, optimization is necessary to ensure feasibility and effective operation of this production system. Therefore, optimization of stocking density, one of the most inluencial parameters (Ljubobratovi�� et al., 2016, Koz��owski and Piotrowska 2024) is essential. This study aimed to evaluate the effects of different stocking densities on growth performance, feed utilization, and physiological status of grow-out sized pikeperch reared in IPRS.
Material and methods
The experiment was conducted over 24 weeks (168 days) from May to September in an IPRS installed in a 0.35 ha pond. A total of 2,304 pikeperch (initial body weight ~160 g) were randomly distributed into three experimental groups: G20 (20 kg.tank-1; 2.78 kg.m-3 ), G40 (40 kg.tank-1; 5.56 kg.m-3), and G60 (60 kg.tank-1 ; 8.33 kg.m-3), each in triplicate. Fish were fed a commercial diet Le Gouessant Percid Grower Flot 5, daily feeding ratio was set between 0.8-1.5% of biomass. Growth, feed conversion ratio (FCR), survival rate (SR), and condition factor (CF) were evaluated. Blood dampling was carried out to assess biochemical profile, haematology and oxidative stress. Dissection of euthanized fish was done to determine organosomatic indices and to sample tissues for oxidative stress analysis. Water quality remained within suitable ranges for pikeperch culture, however with relatively low average temperature (16.84 ± 3.41°C) and moderate dissolved oxygen saturation (79.93 ± 6.08%).
Results and discussion
Growth was comparable among all treatments, indicating that stocking density up to 8.33 kg.m-3 did not negatively affect growth. In contrast, FCR and SR improved significantly with increasing density, with the most favourable values observed in G60 and comparable to RAS based rearing (P��nka et al., 2024, Policar et al., 2016). CF decreased slightly at higher densities, suggesting a leaner body composition. Visceral fat index (VFI) increased markedly during the experiment, with no significant differences among groups, with results similar to published studies (Policar et al., 2024; Ku��era et al., 2025). Biochemical analysis revealed increased hepatic enzyme activity and elevated protein fractions in G40 and G60, indicating intensified metabolic activity and adaptive physiological responses consistent with grow-out. Elevated triglycerides and lipase activity further supported enhanced lipid metabolism at higher densities. Oxidative stress responses were tissue-specific. While mucus showed slightly increased lipid peroxidation and antioxidant activity at higher densities, plasma and liver parameters indicated effective antioxidant defence without systemic oxidative damage. Haematological parameters, particularly increased haematocrit and mean corpuscular volume (MCV) in G40 and G60, suggested compensatory adaptations to lower oxygen availability as previously decribed by Policar et al., (2024). Overall, the observed biochemical, hematological and redox changes represent adaptive responses rather than stress-induced pathology, confirming the suitability and apptness of using higher stocking densities of pikeperch in IPRS.
Acknowledgment
This study was financially supported by the Ministry of Agriculture of the Czech Republic, the project NAZV QL25020009, and by the Ministry of Education, Youth and Sports of the Czech Republic, the OP JAK project Aquaculture for Future CZ.02.01.01/00/23_021/0012616 and the project Biodiversity CZ.02.1.01/0.0/0.0/16_025/0007370.
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