Abstract
Small pelagic fish are key components of marine ecosystems, accounting for 25% of worldwide landings. 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. This phenomenon is thought to be the result of a change in prey quantity and/or quality. Indeed, a recent experiment showed that the growth and body condition of sardines were (i) an immediate response to food quantity (0.3 and 0.6% of the total fish mass in tanks) and pellet size (0.1 and 1.2 mm) and (ii) optimal when sardines consumed large amount of large pellets. Here, we hypothesise that little food (small pellets and/or small quantities) would induce an insufficient supply of n-3 highly unsaturated fatty acids (n-3 HUFA) and constrain the individuals' growth, as n-3 HUFA are essential to vital functions and fitness of fishes. The objective is to investigate food size/quantity effects on n-3 HUFA’ thresholds during the growth of sardines, by measuring the retention rate of n-3 HUFA in muscle from sardines previously conditioned for seven months to four different feeding conditions (small or large pellets, in small or large quantities; n=30 individuals/condition). The analysis of fatty acids will give us an additional element of response to the decreases in growth and body condition of sardines exposed to variable dietary conditioning. It will ultimately contribute to better estimate the consequences of prey quantity and quality on the population dynamics.