Seasonal variations in the total lipid content and fatty acid composition of cultured and wild Crassostrea madrasensis in Sri Lanka

Abstract

The marketplace contains a choice of both cultured and wild oysters, often subtle differences in taste and characteristics are observed between wild and cultured oysters. Therefore, seasonal variations of total lipid and total fatty acid compositions were studied in both, wild and cultured populations of Crassostrea madrasensis in Gangewadiya in Kala-Oya estuary and in cultured populations in the Puttalam lagoon in Sri Lanka over a 13 month period. The fatty acid profile was analyzed using Gas Chromatography. The average lipid percentage was 1.28 ± 0.02% and there was no significant difference between cultured and wild oysters (p > 0.05). A total of 17 fatty acids was detected. Significant monthly variations were seen in all fatty acids, except docosapentaenoic acid (DPA/C22.5(n-3)) and docosahexaenoic acid C226(n-3). Significantly high concentrations (p < 0.05) of omega 3 fatty acids were recorded during October while significantly higher omega 6 concentrations were recorded during April (p > 0.05). Saturated fatty acids had the highest concentration followed by polyunsaturated fatty acids and monounsaturated fatty acids. Palmitic acid was the major saturated fatty acid and docosahexaenoic acid was the major polyunsaturated fatty acid. The ratio of total n-3 PUFA to total n-6 PUFA were 2.6, 2.9 and 3.0 in Gangewadiya wild, Gangewadiya cultured and Kandakuliya cultured oysters, respectively. Though there were no significant differences in omega 3 to omega 6 ratios in cultured and wild oysters in Gangewadiya, a significantly higher ratio was calculated for cultured oysters in Kandakuliya. Hence, a discriminant analysis indicated that in terms of the fatty acid composition, cultured C. madrasensis in Kandakuliya is distinct compared to wild and cultured populations from Gangewadiya. Since, both wild and cultured C. madrasensis shared the same waters in Gangewadiya, the lack of differences can be explained. However, in both sites and under wild and cultured conditions, fatty acid ratio confirms the importance of C. madrasensis as an ideal source of omega 3.