Abstract
Small pelagic fish play important ecological and economic roles. However, a reduction in the size and body condition index of sardines (Sardina pilchardus) has been recorded in the Gulf of Lions since 2008 and in the Bay of Biscay since 2012. A recent experiment showed that the growth and body condition of sardines were (i) an immediate response to food quantity and pellet size and (ii) optimal when sardines consumed large amount of large pellets. Knowing that sardines' prey are rich in n-3 highly unsaturated fatty acids (n-3 HUFA), we hypothesise that small pellets and/or small quantities of food would not meet the n-3 HUFA requirements for an optimal growth of sardines. The objective is to investigate food size/quantity effects on n-3 HUFA’ thresholds. For this, we measured n-3 HUFA content, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in muscle from sardines (n=30 individuals/condition) previously conditioned for seven months to four different feeding conditions: small or large pellets (0.1 vs. 1.2 mm) in small or large quantities (0.3 vs. 0.6% of fish mass). A preferential retention of DHA and EPA seems to take place in polar lipids whatever the diet, unlike neutral lipids. In neutral lipids, sardines fed with small pellets in small quantities have the highest DHA/EPA ratio and DHA percentage over total fatty acids, while those fed with large pellets in large quantities have the lowest values. Fatty acid analysis will ultimately contribute to better estimate the impacts of prey quantity and quality on the population dynamics.