Optimization of inclusion level of glucose and lipid in larval diet of Labeo rohita

Abstract

Formulation and preparation of larval feed according to the requirement of Indian major carp is prerequisite for improving the survival (%) and growth during early developmental stages. A 35-day feeding trial has been executed for the determination of the optimal inclusion levels of fish oil(lipid) and glucose in the diet of Labeo rohita larvae by adding them to graded levels and examining the effects on growth, gut histology, intestinal enzyme activity, in vitro digestibility of macronutrients(carbohydrate and protein), and gene expression. A completely randomized two-factorial feeding trial in triplicate was designed. Two groups of nanoparticulate isonitrogenous(45%CP) diets, the first group with the inclusion of graded levels of glucose G1(2%glu), G2(4%glu), and G3(6%glu) and other groups with 3 levels of lipid, L1(7%), L2(9%), and L3(11%) were prepared. Postlarvae of L. rohita (average body weight 0.4+0.02mg) were evenly distributed in twenty-one troughs (200 larvae /trough or 600 larvae /treatment) at a stocking density of 0.04g/L and aquaria were randomly divided into seven groups and fed their respective diets. At the end of feeding trial, growth performance, gut morphology, activity of intestinal enzymes, in vitro digestibility, and gene expression were studied. Results indicated the significant effect of glucose and lipid inclusion on all studied indices. All pairwise comparisons among glucose inclusion level groups indicated the significant difference in weight gain, specific growth rate, daily weight gain and survival rate of the G2 group followed by the G1 group. Similarly, G2 followed by G1 groups also showed the highest activity of intestinal enzymes, trypsin, amylase, lipase, and protease. The villi height and length showed a similar trend i.e., higher in G2 followed by the G1 group while the G3 group showed the lowest value. The comparison among groups fed lipid inclusion diet indicated higher growth performance (The highest weight gain, specific growth rate and daily weight gain) and survival (%) of the L2 group followed by the L1 group, while the L3 group had suppressed performance even less than a control group. All studied intestinal enzymes except amylase showed a similar trend of L2>L1>control>L3. Amylase showed comparable results among L1, L2 and the control group while L3 showed the lowest value. The villi length and width also showed higher values in L2 followed by L1, while the L3 group showed the lower length and width of villi. Based on growth, intestinal enzyme activity and morphology of the gut, and gene expression of IGF-1 and leptin, 9% dietary lipid and 4% glucose could be recommended to ensure the optimum growth and survival of L. rohita larvae