Responses of juvenile pikeperch (Sander lucioperca) to transfer: stress and adaptation period

Abstract Pikeperch ( Sander lucioperca ) is a commercially valuable freshwater species, mostly produced in Recirculating Aquaculture Systems (RAS). Its high sensitivity to stress remains a challenge for intensive aquaculture production. Tank transfer procedures are commonly used to optimize feeding, reduce cannibalism, and manage stocking density, and are also necessary for scientific experimental protocols aiming to optimize pikeperch production. This study evaluated the physiological stress response following transfer from large (1500 l) to small tanks (350 l) in two pikeperch juvenile stages: on-growing (27.2 ± 7.2 g) and subadults (104.1 ± 14.7 g). Fish were sampled at baseline (B), immediately post-transfer (T), and at 1, 7, 21, 35, and 49 days post-transfer (DPT). Survival exceeded 98%, and specific growth rate remained negative until 7 DPT in both groups. Significant differences ( p < 0.05) were observed in cortisol, which returned to pre-transfer levels by 1 DPT in both groups, and in glucose, which recovered by 7 DPT in on-growing fish and by 1 DPT in subadults. Lactate and ammonia (NH 3 ) recovered by 35 DPT in on-growing and 7 DPT in subadults. Antioxidant enzymes (SOD, CAT) and lipid peroxidation (TBARs) in kidney, gill, and liver recovered by 35 DPT in on-growing and 7 DPT in subadults ( p < 0.05). Overall, larger juveniles exhibited a shorter recovery period, suggesting that they are less sensitive to transfer. These findings provide insights into optimizing pikeperch welfare and growth in aquaculture, as well as for experimental procedures involving transfer to a new environment.