Abstract
This study evaluated the feasibility of biculture rearing of juvenile pikeperch (Sander lucioperca) and Eurasian perch (Perca fluviatilis) in a recirculating aquaculture system. The fish were reared for 98 days in monoculture and biculture groups in five stocking ratios (perch proportion expressed as% pikeperch: P0, P30, P50, P70, P100). Groups with higher proportions of perch (P30, P50) were terminated after 28 days due to perch aggression and high pikeperch mortality. Subsequent analyzes focused only on the ethically viable groups (P100, P70, P0). Eurasian perch showed improved performance in biculture (specific growth rate 1.99 % day−1 vs. 1.51 % day−1 in monoculture) with high survival (94.4–96.3 %). On the contrary, pikeperch survival decreased sharply in biculture (61.5 % in P70 vs. 94.7 % in P100), while the specific growth rate remained similar (1.50 % day−1). Elevated glucose and triglyceride levels in bicultured pikeperch indicated chronic stress. Fin erosion remained generally low in both species. Overall, Eurasian perch consistently outcompeted pikeperch, leading to compromised welfare and high mortality in pikeperch. Biculture of these two predatory percids under conditions of an intensive recirculating aquaculture system is impractical.
Materials and methods
The 98-day trial was carried out in 15 cylindrical plastic tanks (380 L each, initial density 3.61 kg m−3, 120 fish per tank) connected to an experimental recirculating aquaculture system at the University of South Bohemia, Faculty of Fisheries and Protection of Waters, Vodňany, Czech Republic. The light regime was 12L:12D (7 lux at the water surface). The quality was maintained at 21.9 ± 0.56 °C, dissolved oxygen 104.87 ± 17.35 %, pH 6.99 ± 0.22, ammonia 0.37 ± 0.23 mg L−1, and nitrite 0.51 ± 0.18 mg L−1. The fish (four months old) came from combined pond-intensive production. Five stocking ratios were tested in triplicate using automatic feeders (8-hour intervals) with a daily feed ration of 1.5 % of total biomass (adjusted every 28 days). Growth parameters, organosomatic indices, blood biochemistry, and fin condition (0–3 scale) were evaluated. Data were analysed by one-way/two-way ANOVA or Kruskal-Wallis test followed by Tukey's/Dunn's post-hoc test (p < 0.05).
Results
Significant differences (p < 0.05) were found in survival and specific growth rate (Table 1). Pikeperch survival was markedly lower in biculture (61.5 % in P70) than in monoculture (94.7 % in P100), while Eurasian perch maintained high survival (94.4–96.3 %) and achieved higher specific growth rate in biculture (1.99 % day−1) than in monoculture (1.51 % day−1). Fin erosion was low and not treatment-dependent. Pikeperch in biculture showed elevated plasma glucose and triglycerides, indicating chronic stress. Fat somatic index was significantly higher in bicultured Eurasian perch.
Discussion
The strong competitive imbalance observed demonstrates that Eurasian perch consistently outcompeted pikeperch for resources, leading to suppressed welfare and high mortality in pikeperch despite comparable growth rates (Amoussou et al. 2022b; Thomas et al. 2022). Elevated stress markers in bicultured pikeperch and improved fat deposition in Eurasian perch confirm behavioural dominance rather than direct physical aggression as the main limiting factor. These results align with previous findings on percid polyculture, where ecological niche overlap prevents successful co-rearing (Pěnka et al. 2024a; Policar et al. 2019).
Conclusions
Biculture of juvenile pikeperch and Eurasian perch in recirculating aquaculture systems is impractical due to severe competitive imbalance, reduced pikeperch survival, and welfare concerns. Monoculture or carefully selected species combinations with complementary ecological niches are recommended for percid aquaculture.
Acknowledgment
This study was financially supported by the Ministry of Agriculture of the Czech Republic (project NAZV QL25020009) and by the Ministry of Education, Youth and Sports of the Czech Republic (OP JAK project Aquaculture for Future - CZ.02.01.01/00/23_021/0012616).
References
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