Dietary zinc requirement of fingerling Indian major carp, Labeo rohita (Hamilton)

Abstract

The current investigation was carried out to estimate the requirement of dietary zinc for fingerling Labeo rohita (6.3 ± 0.09 cm; 2.12 ± 0.08 g) by feeding casein-gelatin based seven isonitrogenous (350 g kg−1 crude protein) and isoenergetic (16.7 kJ g−1 gross energy) diets with incremental levels of zinc (9.52, 19.73, 29.84, 51.42, 71.91, 93.14 and 112.32 mg kg−1 diet). The experimental diets were hand-fed to triplicate group of fish at 08:00, 12:00 and 16:00 h to apparent satiety for 8-week. Significant improvement (P < .05) in live weight gain (LWG), specific growth rate, protein efficiency ratio, protein gain and feed conversion ratio were evident in fish fed incremental zinc levels up to 51.42 mg kg−1 (Zn4). No significant differences in the body protein and moisture contents were noted. However, body fat content decreased and ash content increased significantly with increment in zinc levels up to 51.42 mg kg−1 diet (Zn4). Zinc concentration in the whole body, liver, scales, vertebrae and serum significantly enhanced (P < .05) with increment in zinc levels up to 51.42 mg kg−1 diet and then levelled off. Fish fed basal diet (Zn1) containing 9.52 mg kg−1 dietary zinc exhibited significantly highest apparent zinc retention compared with other dietary treatment groups. The magnesium and iron contents in the whole body, liver, scales and vertebrae were significantly affected by the increasing levels of dietary zinc, but no change (P > .05) was noted in calcium and phosphorus concentrations. Haematological parameters such as haematocrit, haemoglobin, red blood cell counts, mean cell volume and mean cell haemoglobin were significantly affected (P < .05) excepting the mean cell haemoglobin concentration. Serum superoxide dismutase, glutathione peroxidase, catalase and alkaline phosphatase (ALP) activities responded positively (P < .05), while malondialdehyde concentration responded negatively up to 51.42 mg kg−1 dietary zinc level. Broken-line regression analysis of LWG, whole body, scales, vertebrae and serum zinc content, and ALP activity against dietary zinc concentrations indicated the break points at 50.90, 51.23, 49.19, 48.52, 52.93 and 47.85 mg kg−1 diet, respectively. Based on the above results of this investigation, inclusion of dietary zinc in the range of 47.85–52.93 mg kg−1 is recommended for L. rohita fingerlings for maintaining optimal growth, haematological parameters, tissue zinc concentration and antioxidant status.