Growth Performance, Nutrient Utilization, Metabolic and Digestive Enzymes Studies in Mrigal (Cirrhinus mrigala) Juveniles Fed Graded Levels of Carbohydrate

Abstract

A 45-day experiment was carried out to evaluate the growth performance, digestive enzyme activity, and gene expression in mrigal fish Cirrhinus mrigala, fed graded levels of carbohydrate. Three isonitrogenous and isolipidic diets containing either 30, 40 or 50% carbohydrate were formulated using purified ingredients. One hundred and eight Cirrhinus mrigala fingerlings (av. wt. 5.83-6.08g) were equally divided into three groups in 9 plastic tanks of 150L capacity each. Each of the three experimental diets was fed to triplicate groups of fish held under natural light cycle of 12h daylight and 12h darkness. % Weight Gain (WGR), specific growth rate (SGR), feed conversion ratio (FCR) and hepato-somatic index (HSI) were evaluated and found to vary significantly (P<0.05) in relation to the level of carbohydrate in the experimental diets. No significant difference (P>0.05) was found in % weight gain, SGR, and FCR, between the 30% and 50% carbohydrate fed groups but HSI increased significantly across the inclusion levels. Amylase enzyme activity was highest in 40% fed group relative to the 30% and 50% groups. Chymotrypsin and trypsin activities were not significantly different between the 40% and 50% carbohydrate fed groups. Various metabolic enzyme activities in the muscle [aspartate aminotransferase (AST), alkaline amino transaminase (ALT) and malate dehydrogenase (DH)] varied significantly (P<0.05) in response to increased levels of carbohydrate. Gene expression among the digestive enzymes reflected both transitional and translation effect; amylase and trypsin exhibited higher expression with the increasing level of carbohydrate of the experimental diets but results were reversed for chymotrypsin expression. In our study, gene expression was initially significantly higher but then decreased. No consistent pattern was found among the different digestive enzymes.