Requirement of fingerling Indian major carp, Labeo rohita (Hamilton) for dietary iron based on growth, whole body composition, haematological parameters, tissue iron concentration and serum antioxidant status

Abstract

To estimate the requirement of fingerling Labeo rohita (6.4 ± 0.10 cm; 2.23 ± 0.05 g) for dietary iron, the present study was conducted by feeding seven casein-gelatin based isonitrogenous (350 g kg−1 crude protein) and isoenergetic (16.7 kJ g−1 gross energy) diets with different levels of iron (13.2, 65.4, 116.2, 165.6, 218.8, 312.5 and 427.3 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. Live weight gain (LWG; 874%), specific growth rate (4.06% day−1), feed conversion ratio (1.46), protein efficiency ratio (PER; 1.96) and protein gain (PG; 3.27 g fish−1) improved (P < 0.05) with the increase in iron levels from 13.2 to 165.6 mg kg−1 diet. Dietary iron levels significantly influenced whole body moisture, protein and lipid content. Tissue iron concentration and haematological indices such as haematocrit (Hct), haemoglobin (Hb) and red blood cell counts (RBCs) increased linearly (P < 0.05) with increase in levels of iron up to 218.8 mg kg−1 diet and then stabilized. Serum iron concentration, superoxide dismutase, glutathione peroxidase and catalase activities responded positively up to 218.8 mg kg−1 dietary iron, whereas malondialdehyde content responded negatively up to the above level of dietary iron. Quadratic regression analysis of growth parameters such as LWG and PG, and broken-line regression analysis of liver iron concentration, Hct, Hb, and serum iron concentration against different dietary iron levels revealed the requirements at 265, 262, 238, 211, 238 and 218 mg kg−1 diet, respectively. Judging from the regression analyses, dietary iron requirement in the range of 211–265 mg kg−1 diet is recommended for fingerling L. rohita for maximizing growth, maintaining normal tissue iron concentration and haematological parameters, and improved antioxidant activities.