Effects of elevated carbon dioxide on growth, feed efficiency and physiological responses in RAS-based juvenile pikeperch (Sander lucioperca)

Carbon dioxide (CO 2 ) accumulation is a major concern in recirculating aquaculture systems (RAS), where elevated levels can negatively affect fish growth and welfare. Although the effects of CO 2 on pikeperch ( Sander lucioperca ) have been studied, long-term tolerance under production conditions is not well documented. This study investigated the effects of three concentrations of dissolved CO 2 (5 mg L −1 = Low; 15 mg L −1 = Medium; 30 mg L −1 = High). On the growth performance, conditional parameters, and physiological status of juvenile pikeperch reared for 105 days in RAS. Fish (initial total length 250.9 ± 20.7 mm; initial weight 117 ± 28.2 g) were stocked in three tanks for treatment and fed at 1% biomass. Fish in the High group showed significantly lower final weight (233 g) than fish in the Low (297 g) and Medium (250 g) groups, correlated by a reduced Fulton's condition factor and a significant increase in feed conversion ratio (1.09–1.82). Other production parameters, survival rate, organosomatic indices, fin erosion did not show significant differences between groups. Biochemical parameters highlighted stress and reduced protein metabolism under high CO 2 . Total plasma protein, albumin and globulin were significantly lower in the High group, while plasma ammonia and cortisol increased significantly in group High. These results indicate that CO 2 concentrations above 15 mg L − 1 impair growth, feeding efficiency and physiological condition of juvenile pikeperch, highlighting the need for strict CO 2 control in RAS.