Dietary potassium requirement of fingerling Indian major carp, Labeo rohita (Hamilton), based on growth parameters, gill Na+-K+ ATPase activity, tissue mineralization and antioxidant activities

To quantify the dietary potassium requirement of fingerling Labeo rohita (6.2 +/- 0.12 cm; 1.98 +/- 0.06 g), seven purified experimental diets (350 g/kg crude protein and 16.72 kJ/g gross energy) with graded levels of potassium (0.32, 1.35, 2.41, 3.46, 6.48, 9.47 and 12.39 g/kg diet) were fed to triplicate groups of fishes at 08:00, 12:00 and 16:00 hr to apparent satiation for 8 weeks. Live weight gain (LWG; 671.46%), specific growth rate (3.65%/day), protein efficiency ratio (2.16), protein gain (PG; 2.41 g/fish) and feed conversion ratio (1.32) were found to be best in fish fed diet containing 3.46 g/kg potassium. Gill Na+-K+ ATPase activity was also highest in fish fed diet with 3.46 g/kg potassium. Potassium content of whole-body, vertebrae and scales increased significantly with the increase in dietary potassium level up to 6.48 g/kg. Significant changes were also noted in serum malondialdehyde content, superoxide dismutase, catalase, glutathione peroxidase and alkaline phosphatase activity. Based on the maximum live weight and protein gain observed in the present study, the inclusion of 3.55 g/kg potassium is recommended for developing potassium-balanced commercial feeds for intensive culture of fingerling L. rohita.