Effects of species composition on growth and rearing efficiency in juvenile pikeperch (Sander lucioperca) and Eurasian perch (Perca fluviatilis) reared alone and together in RAS

This study evaluated the feasibility of biculture rearing juvenile pikeperch (Sander lucioperca) and Eurasian perch (Perca fluviatilis) in a recirculating aquaculture system (RAS). Fish were reared for 98 days in monoculture and biculture groups at five stocking ratios, with perch proportion expressed as % of pikeperch (P0, P30, P50, P70, P100). Groups with higher perch proportions (P30, P50) were terminated after 28 days due to perch aggression and high pikeperch mortality. Subsequent analyses focused only on the ethically viable groups (P100, P70, P0). In these remaining treatments, Eurasian perch showed improved performance in biculture, with higher specific growth rate (SGR; 1.99%.d−1) compared to monoculture (1.51%.d−1), alongside consistently high survival (94.4–96.3%). In contrast, pikeperch in the P70 group (94.7% in P100 vs. 61.5% in P70) and specific growth rate was consistent across P70 and P100 (SGR = 1.50%.d−1). Elevated glucose and triglyceride levels in blood plasma of bicultured pikeperch indicated chronic stress, while Eurasian perch in P70 showed higher fat somatic index and lower ammonia level in blood plasma, reflecting enhanced nutritional status. Fin erosion remained generally low in both species, suggesting that competitive disadvantages in pikeperch resulted primarily from behavioral interference rather than direct physical aggression. Overall, results reveal a strong competitive imbalance: Eurasian perch consistently outcompeted pikeperch for resources, leading to compromised welfare, suppressed growth, and high mortality in pikeperch. We conclude that biculture of these two predatory percids under intensive RAS conditions is impractical. Thorough evaluation of interspecific interactions is essential before implementing bi- or poly-culture strategies in commercial percid aquaculture.