Effects of elevated carbon dioxide on growth, feed efficiency and physiological responses in RAS-based juvenile...

Carbon dioxide (CO₂) accumulation is a major concern in recirculating aquaculture systems (RAS), where elevated levels can negatively affect fish growth and welfare. Although the effects of CO₂ 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 CO₂ (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 CO₂. 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 CO₂ concentrations above 15 mg L^-1 impair growth, feeding efficiency and physiological condition of juvenile pikeperch, highlighting the need for strict CO₂ control in RAS.