Effects of dietary lipid levels on growth, feed utilization, RNA/DNA ratio, digestive tract enzyme activity, non-specific immune response and optimum inclusion in feeds for fingerlings of rohu, Labeo rohita (Hamilton)

Abstract

The current investigation was conducted to assess the effects of different levels of dietary lipid on growth performance, feed utilization, digestive tract enzyme activity, lipid deposition, and non-specific immune response of fingerling Labeo rohita (2.23 ± 0.06 g). Six isonitrogenous (400 g kg−1) purified diets with increasing levels of lipid (20, 40, 60, 80, 100, 120 g kg−1 diet) were fed to triplicate groups of 30 fish per tank at 08:00, 12:00, and 16:00 h to apparent satiety for 8 weeks. Absolute weight gain (AWG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE) and RNA:DNA ratio improved significantly (P < 0.05) up to 100 g kg−1 lipid in diet. Somatic indices and whole body lipid positively correlated with the increase in dietary lipid. Dietary lipid levels significantly affected hepatic antioxidant activities. Liver superoxide dismutase (SOD) and catalase (CAT) activities improved significantly up to 100 g kg−1 lipid in diet. However, liver thiobarbituric acid reactive substances activity (TBARS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities showed a negative correlation with the increase in levels of lipid in the diets. Highest intestinal protease and lipase activity was also noted in fish received 100 g kg−1 lipid in diet. Second-order polynomial analysis of AWG, FCR, RNA/DNA ratio, SOD and serum lysozyme activity against varying levels of dietary lipid reflected the requirement in the range of 94.77–98.35 g kg−1 dietary lipid for optimum growth of L. rohita.