Impact of Vitamin C on Growth, Haemato‐Immunological Characteristics and Stress Tolerance Capability of Climbing Perch, <i>Anabas testudineus </i> (Bloch, 1792)

ABSTRACT Climbing perch, Anabas testudineus , were fed four diets: D0, D500, D1000 and D1500, containing 0, 500, 1000 and 1500 mg of vitamin C per kg of basal diet, respectively, over 70 days. After the growth trial, significantly higher final weight, percent body weight (%WG) and specific growth rate (SGR) were observed in fish fed D1000 followed by D500 and D0 diets. However, D1500 diet‐fed fish had a significantly lower growth performance among all diet groups. The best feed conversion ratio and protein efficiency ratio were observed in fish fed D1000, followed by D500, with no significant difference between D0 and D1500 groups. Blood parameters were significantly influenced by vitamin C dosages. Fish fed on the D1000 diet exhibited significantly higher white blood cell (WBC), monocyte (MONO) and granulocyte (GRA) counts among all dietary groups. Vitamin C supplementation significantly increased platelet count in the D1000 group. Haemoglobin, haematocrit and red blood cell (RBC) counts showed an increasing trend with higher vitamin C levels, with the highest values in fish fed D1500 followed by D1000 diet. Total immunoglobulin (Ig) content was significantly higher in fish fed D1000 and D1500 diets compared to others, while peroxidase and catalase activity remained unaffected by the vitamin C levels. Vitamin C supplementation enhanced the salinity stress tolerance of fish, with the highest lethal time of 50% mortality (LT50) observed in the D1000 group, while other groups showed intermediate values. The polynomial regression analysis of %WG, LT50, WBC and Ig revealed that the optimum vitamin C supplementation levels were 773.75, 866.67, 934.71 and 1062.5 mg/kg diet, respectively, for climbing perch; these values are also in line with most of the growth and health performance parameters of the fish.