Partial replacement of fish meal with <em>Azolla</em> meal in diets for Nile tilapia (<em>Oreochromis niloticus</em> L.) affects growth and whole body fatty acid composition

Abstract

The replacement of fishmeal (FM) with Azolla meal (AM) in diets on growth and fatty acid in Nile tilapia, Oreochromis niloticus (initial mean weight: 16.4 g) was studied. Fish were fed with six isonitrogenous (29.2% CP) and isoenergetic (16.9 kJ.g^-1) diets containing 0%, 10%, 20%, 30%, 40% and 50% AM respectively, as partial FM substitute. Diet A0 acted as a control. The final weight (51.0-88.3 g), the weight gain (210.8-438.3%) and the SGR (1.3-1.9%day^-1) decreased when AM level higher than 10% in diets (P < 0.05). The FCR (1.44 to 2.35) significantly increased when AM level exceeded 20% (P < 0.05). The protein efficiency ratio and the apparent net protein utilization decreased consequently. The fatty acids in the whole fish were significantly influenced by the diets. The replacement of FM by AM produced fish with lower (n-3) highly unsaturated fatty acids mainly docosahexaenoic acid, and higher arachidonic acid (P < 0.05). The n-3/n-6 fatty acid ratio ranged from 0.08 to 0.17, and was lower in fish fed A₄₀ and A₅₀ (P < 0.05). The findings suggest that high AM in diets affects Nile tilapia growth and the fern could be incorporated in diets up to 30% without any adverse effect on fish fatty acid composition. However, alternative additional source of lipid must be used to improve the quality of fish fed AM-diets.

Keywords: Azolla, Fish meal replacement, Growth, Fatty acids, Oreochromis niloticus, bioconversion