Chloramine T in pikeperch ( <i>Sander lucioperca</i> ) aquaculture. Safeguard or hidden threat? Evaluating its effect on fish growth, immune response and liver function

Abstract Introduction Chloramine T (CLT) is utilised in aquaculture for its disinfectant and antiseptic properties, yet its physiological effects on fish health remain underexplored, particularly in emerging species like pikeperch ( Sander lucioperca ). This study assessed the impact of CLT exposure on growth performance, immune response and liver function in pikeperch reared in recirculating aquaculture systems (RAS). Material and Methods A total of 270 fish were assigned to a control group (C), a single-bath group (10 mg L −1 , day 0; CLT1) and a three-bath group (10 mg L −1 on days 0, 7 and 14; CLT3). Fish were reared in independent RAS units under stable physicochemical conditions. Growth performance was monitored, and blood and tissue were sampled. Liver enzyme (ALT, AST and alkaline phosphatase), serum lysozyme and ceruloplasmin activities, phagocyte function, lymphocyte proliferation and liver histopathology were assessed. Results Growth parameters and condition factor (ratio of body weight to the cube of body length) remained stable across all groups, and no mortality was observed. Liver enzyme activities showed no significant alterations; however, inflammatory changes were noted in the liver in the CLT3 group. Serum lysozyme activity increased after the initial exposure, indicating an acute immune response. In contrast, repeated exposure reduced respiratory burst and phagocyte killing activity, suggesting immunosuppression; however, CLT3-group T and B lymphocytes proliferated more as a reaction to inflammation. Conclusion While CLT at 10 mg L −1 is indicated to be generally safe for pikeperch under controlled RAS conditions, repeated exposures may induce mild hepatic inflammation and temporary immune modulation. This study offers insights into optimising the use of CLT in aquaculture to ensure efficacy and safety.