Effect of dietary protease at different levels of malic acid on growth, digestive enzymes and haemato-immunological responses of Nile tilapia, fed fish meal free diets

Abstract

This study evaluated the dose response to dietary exogenous protease enzyme or malic acid inclusion in plant-based diets on the growth, digestive enzymes and haemato-immunological indices in Nile tilapia, Oreochromis niloticus. Nine isonitrogenous (293 g kg−1 crude protein) and isocaloric (14.80 MJ kg−1 metabolizable energy) diets were formulated to feed juvenile tilapia (average initial weight, 7.56 ± 0.06 g) in a 3 × 3 factorial feeding trial for 84 days. Diets were formulated to contain three levels of exogenous protease (0, 2500 and 5000 U kg−1), and each level was supplemented with three levels of malic acid (0, 5 or 10 g kg−1 diet). The lowest pH level of the stomach and gut was recorded in fish fed diet containing 2500 and 5000 U protease kg−1 at 10 g malic acid. Both protease enzyme and malic acid significantly improved (P < .05) the growth responses of fish. Additionally, the activity of intestinal chymotrypsin, trypsin and lipase were significantly (P < .05) higher in experimental diets containing 2500 or 5000 U protease kg−1 at 5 g kg−1 malic acid. The highest hemoglobin, hematocrit, red blood cells, serum total protein, albumin and globulin values were observed in fish fed diets containing 2500 or 5000 U protease kg−1 at 5 g malic acid kg−1. The optimal activity of alanine and aspartate aminotransferase and alkaline phosphatase was detected in fish fed either 2500 or 5000 U protease kg−1 at 5 g malic acid kg−1. Data suggests that adding exogenous sources of protease enzymes in combination with malic acid at 5 g kg−1 in plant protein-based diet improved growth performance; feed utilization efficiency, digestive enzymes and health status of Nile tilapia.