Nutritional quality in terms of lipid content and fatty acid composition of neutral and polar lipids in the adductor muscle of the oyster Crassostrea gigas (Thunberg, 1794) farmed in the Bizert lagoon (Tunisia) in relation with sexual cycle and environmental settings

Monthly variations of fatty acid composition of the two fractions polar lipids (PL) and neutral lipids (NL) in the adductor muscle of cupped oyster Crassostrea gigas, were studied from May 2005 until June 2006 in the Bizert lagoon, related to environmental parameters and reproductive events. C. gigas showed a clear cycle of energy storage and utilization in the site of study. Total PL and NL content varied significantly during the year and showed a negative and significant correlation with the gametogenic condition index which can be explained by transfer of fatty acids from the adductor muscle to gonads to support the gametogenic cycle. Nevertheless, PL and NL have no significant correlations either with temperature or chlorophyll a registered in the site of study. The adductor muscle proved to be less influenced by chlorophyll a richness of the farming environment. The dominance of total polyunsaturated fatty acids (PUFAs) over the saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) in both PL and NL fractions was established throughout the period of study. Oysters analyzed were characterized by high levels of PUFAs n−3 and high n−3/n−6 PUFAs ratio in both PL and NL fractions. PUFAs n−3 and SFAs of PL and PUFAs and SFAs of NL, showed a negative and significant correlation between them. In fact, low temperature values produce generally an increase in the PUFAs percentages in order to maintain the fluidity of cell membranes. We deduce that annual variations of fatty acids content in PL and NL fractions of the adductor muscle of C. gigas seem to be in relation with the reproductive events. According to our results, the adductor muscle tissues were relatively poor in fatty acids (maximum values (% of dry weight) of PL and NL respectively were 2.04±0.33 and 1.75±0.9). Lipids fluctuations were not pronounced all over the period of study in the site of sampling due to low effects of the environment richness and phases of the sexual cycle which aspires the adductor muscle contents of fatty acids to support other organs in the gametogenic process. But this organ arrives despite its difficulties to maintain a high level of n−3/n−6 PUFA and having a good nutritional quality.