Fatty-acid biomarkers and tissue-specific turnover: validation from a controlled feeding study in juvenile Atlantic croaker Micropogonias undulatus.

Fatty-acid (FA) profiles of liver and muscle tissue from juvenile Atlantic croaker Micropogonias undulatus were examined over a 15 week diet-switch experiment to establish calibration coefficients (CC) and improve understanding of consumer-diet relationships for field applications. Essential FAs [docosahexaenoic acid (DHA), 22:6n-3 and eicosapentaenoic acid (EPA) , 20:5n-3] decreased and 18:2n-6 increased in tissues of M. undulatus fed diets with increasing proportions of terrestrial v. marine lipid sources. Non-linear models used to estimate the incorporation rate and days to saturation of per cent 18:2n-6 in tissues showed that livers incorporated 18:2n-6 faster than muscle, but the proportions of 18:2n-6 in muscle were higher. CCs were established to determine proportions of FA deposition in tissues relative to diet. Many CCs were consistent amongst diet treatments, despite growth and dietary differences. The CCs can be used to discern FA modification and retention within tissues and as tools for future quantitative estimates of diet histories. Incorporation rates and CCs of 18:2n-6 were applied to a sub-set of field samples of wild M. undulatus to understand habitat use and feeding ecology. Altogether, these results suggest that FAs provide a time-integrated measure of diet in aquatic food webs and are affected by tissue type, growth rate and the influence of mixed diets.