Nutritional importance of minor dietary sources for leaping grey mullet Liza saliens (Mugilidae) during settlement: insights from fatty acid δ13C analysis
Résumé
The present case study combined fatty acid analysis and compound-specific carbon isotopic analysis of fatty acids in order to trace changes in dietary sources of essential fatty acids during settlement of the estuarine fish Liza saliens (Mugilidae) in its lagoon nursery. Compositional and isotopic shifts in neutral and polar lipid-derived fatty acids were analysed separately, as these 2 lipid classes are thought to integrate dietary isotopic signals differently. An increase of 5‰ in the δ13C of many fatty acids in settled fish indicated that they had shifted from planktonic to benthic resources during settlement. However, the sharp decrease in the proportion of 22:6ω3 in settled fish and the fact that this specific fatty acid kept a planktonic δ13C signature revealed that benthic resources could not provide this compound, in contrast to 20:4ω6 and 20:5ω3 for which δ13C shifted towards more benthic values. Consequently, although the production of settled fish was essentially supported by benthic dietary sources, as confirmed by biomarker results, minor reliance on planktonic dietary sources was required to provide fish with 22:6ω3. The lag between the increase in δ13C in fatty acids derived from neutral and polar lipids suggested that neutral lipid fatty acids integrated the dietary isotopic signal faster. These contrasting dynamics highlight the importance of analyzing lipid classes separately when fast dietary shifts are expected, and could be used to obtain dietary information over different time scales.