Influence of season on the lipid content and fatty acid profiles of three tilapia species (Oreochromis niloticus, O. macrochir and Tilapia rendalli) from Madagascar

Lipids extracted from three tilapia species (Oreochromis niloticus, O. macrochir and Tilapia rendalli) of mean weight 100-250 g collected in Itasy lake of Madagascar highlands during three seasons, were analyzed for their fatty acid compositions. The muscle fishes contained less than 1.4% lipid by weight. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS), allowed identification of more than 40 fatty acids and 30 of them were quantified in muscle tissue lipids of fishes. Among them, those occurring in the highest proportions were palmitic, stearic, oleic, palmitoleic and linoleic acids. The main polyunsaturated fatty acids were arachidonic acid, eicosa-5,8,11,14,17-pentaenoic acid (EPA) and docosa-4,7,10,13,16,19-hexaenoic acid (DHA). The relative amount of these acids changed significantly between species and season of collect, in particular DHA which decreased from 11.4% to 6.0% for O. macrochir during the spring to autumn period. For O. niloticus and T. rendalli, DHA decreased from 9.8% to 4.9% and to 10.1% to 4.4%, respectively during the same period. Therefore the ∑n−3/∑n−6 ratios vary, for each species according to season of collect, being lower in autumn (0.5-0.6) and raising up to 0.7-1.6 in winter. Multivariate statistical analyses, starting from the fatty acid composition, lipid percentage and biometric ratio (weight/size) data of 113 samples, reveals significative differences between species and season of collect. Furthermore differences in fatty acid profiles are higher within season than species. The results show that wild tilapias from tropical lakes of the Madagascar highlands possess beneficial properties and therefore contribute significantly of the n−3 fatty acids intake of the local population diet.