Crude glycerin as dietary energy source for Nile tilapia

Abstract

Biofuels are a renewable and clean alternative to keep up with the increasing demand for energy. Biodiesel stands out among biofuels, but its production yields crude glycerin [CGL] as a result of the transesterification process. The increased availability and low cost of CGL encourage the assessment of digestibility of glycerin as dietary energy source, and growth, hematological parameters and carcass composition of Nile tilapia fed diets containing crude glycerin. The apparent digestibility coefficient of energy from dietary glycerin (indirect method, chromium III oxide as inert marker) was 79.41%, corresponding to 12.04MJkg-1. Juvenile tilapia (7.73±0.09g) were stocked into 300-L, indoor plastic tanks (12 fish per tank), closed-loop recirculating system under continuous in a totally randomized experimental design (n = 4), and fed to apparent satiation for 90days with isonitrogenous and isocaloric diets containing 0, 4, 8, 12 and 16% of CGL. At the end of feeding trial, fish were measured and weighted; blood samples of were drawn from the caudal vein of two fish per tank and two fish from each replicate were euthanized for analysis of carcass proximate composition. Data were subjected to one-way ANOVA (α = 0.05) and optimum dietary crude glycerin level was determined by polynomial regression analysis. Weight gain, feed intake, feed conversion ratio, protein retention efficiency and specific growth rate were significantly affected by dietary CGL contents. Weight gain fitted a second-degree equation and the optimum inclusion level was estimated at 5.9%, but up to 12% dietary crude glycerin did not impair growth performance of fish. Increasing dietary CGL levels did not affect hepatosomatic, liposomatic and viscerosomatic indices, as well as survival rate, proximate composition of tilapia carcass and hematological parameters. Crude glycerin seems to be an interesting and safe source of energy for Nile tilapia. © 2014 Elsevier B.V.