Growth and physiological response of Labeo rohita larvae to dietary Se and Shilajit at various inclusion level during early development

Abstract

The nutritional requirement of fish larvae remains a limiting factor in advanced aquaculture. Micronutrients are crucial for early development; however, their inclusion level has not been standardized in the larval feed of carps. The present study was executed to determine the optimum dietary inclusion level of two additives, i.e., selenium and Shilajit in the larval feed of Rohu, Labeo rohita. Two sets of feeding trials in triplicate under semi-control conditions were conducted for 35-days. For the first set of experiments, the organic form of nano-selenium methionine (SeMet) was prepared by chemical method. For feeding, trial larvae were evenly distributed in 21 troughs at the rate of 200 larvae/trough with a stocking density of 0.04g/L. The troughs were randomly divided into seven groups and fed their respective diet. The first group was provided with a Nanoparticulate basal diet (without supplement) and assigned control group while three groups SS(0.5), SS(1) and SS(1.5) were fed a nanoparticulate diet supplemented with graded levels (0.5mg/kg, 1mg/kg,1. 5mg/kg diet) of the inorganic form of selenium (sodium selenite). The last three groups (SM0(0.5), SM(1), SM(1.5) were fed with a diet supplemented with nano SeMet at the same three inclusion levels. Results indicated the most significant positive effect of a 1mg/kg diet of SeMet on growth performance (WG (%), SGR, survival (%), digestive enzymes (protease, amylase, lipases & trypsin), antioxidant enzymes (SOD, CAT, POD, GSH-Px) and the growth gene (IGF-1).In contrast LPO level and innate immune response gene (HSP-70) was downregulated at the inclusion level of 1mg/kg diet of SeMet. Histomorphometric analysis of the intestine of the SM(1) group also indicated the most significant increase in intestinal villi height and villi width as compared to other groups especially groups fed sodium selenite supplemented diets. Moreover, supplementation of inorganic selenium and organic selenium above 0.5 and 1.0 mg/kg diet respectively, showed negative effects on all studied indices of larvae during early rearing. The second set of experiments was also conducted in triplicate troughs at the same stocking density under semi-static conditions. The larvae were distributed in 4 groups, i.e., C0, SJ(3), SJ(5) and SJ(7) and fed a basal diet supplemented with 0, 3, 5 and 7g shilajit respectively for 35 days. At the end of the feeding trial, larvae reared on a 5g shilajit /kg diet showed comparatively the best growth performance, the highest activity of digestive enzymes (protease, amylase, DRSML QAU vi lipase and trypsin), improved antioxidants enzymes status, decreased LPO level and HSP-70 expression. Intestinal morphology (villi length, width, tunica muscular thickness and absorptive area of villi) was also increased significantly. Based on the results (growth performance, digestive enzymes, antioxidant activity, intestinal morphology and gene expressions) 1mg /kg diet SeMet while 5g/kg diet shilajit could be considered the optimum level and recommended for the early rearing of rohu larvae. Keywords: Selenium, Shilajit, antioxidants, rohu, larvae, intestinal morphology