Effects of dietary malic acid on growth, nutrient utilization and serum biochemical indices of Nile tilapia (Oreochromis niloticus) fingerlings

A 90 days feeding trial was conducted to investigate the effect of dietary supplementation with malic acid on growth, nutrient utilization and some hematological parameters of Nile tilapia (Oreochromis niloticus). Three isonitrogenous (300 g CP kg⁻¹) and isocaloric (14.90 MJ gross energy kg⁻¹) diets were formulated. The control diet (D1) contained no added of malic acid. Two diets were supplemented with 0.5% (D2) and 1.0% (D3) malic acid. A set of 180 fish of O. niloticus L. mono-sex male fingerlings average initial weight of 7.56 ±0.06 g were randomly distributed into nine plastic tanks (0.45 m³ for each) representing the three treatments studied. Twenty fish were randomly stocked into each tank with three replications for each treatment. At the end of the feeding trial, O. niloticus offered the control diet showed lower growth and feed utilization than all those fed malic acid supplemented diets. Fish fed the diet D3 showed the highest body weight (BW) weight gain (WG), specific growth rate (SGR), feed intake (FI), and the best feed conversion ratio (FCR) and protein efficiency ratio (PER). Supplementation of malic acid (5 g or 10 g kg^-1) increased hemoglobin (Hb), hematocrit (Htc) and red blood cell count (RBCs) of Nile tilapia, but white blood cells (WBCs) of did not significantly (P>0.05) affected by malic acid supplementation. The highest level of Hb, Htc and RBC was recorded by fish fed 10 g kg^-1. In the same direction supplementation the basal diet with 5 g or 10 g kg^-1 malic acid significantly increased the levels of serum Albumin u/L (P<0.001), Globulin (P<0.05) and total protein (P<0.001). The present observations suggest that, growth and feed utilization of O. niloticus can be enhanced with a supplementation of 1.0% malic acid in the diet.