Recent advances in lipid nutrition in fish larvae

Due to the importance of dietary lipid utilization for larval rearing succe ss, increasing attention has been paid during the last years to different a spects of larval lipid nutrition such as digestion, absorption, transport a nd metabolism, which are frequently studied by different research groups. T he present study reviews the published information on these aspects, includ ing some recent results obtained in our laboratory, that contribute to a be tter understanding of larval lipid nutrition. Neutral lipase activity was found in the digesta of larval gilthead seabrea m as early as first feeding, followed by a significant increase which reach ed up 8 times the initial levels at day 15 and was clearly influenced by th e fatty acid composition of dietary lipids. Accordingly, the capacity for l ipid absorption by the intestinal epithelium has been also observed at the onset of exogenous feeding, although the specific location in the different digestive tract segments differ with species. Whereas the capacity to abso rb lipid increases with development in live prey-fed larvae, this improvemm ent is delayed in larvae fed formulated diet. Increasing dietary phosphatid yl cholines levels enhanced lipid absorption regardless of whether it is of soybean or marine origin, but the latter improved hepatic lipid utilizatio n. Enzymatic, histological and biochemical evidences suggest that marine fi sh larvae are able to effectively digest and absorb n-3 HUFA-rich triacylgl ycerols, but feeding with phosphoacylglycerols, particularly if they are ri ch in n-3 HUFA, would enhance phosphoacylglycerols digestion and specially lipid transport alowing a better n-3 HUFA incorporation into larval membran e lipids and promoting fish growth. Although the essentiality of n-3 HUFA f or larval marine fish has been studied extensively, only recently has the i mportance of dietary arachidonic acid in the larvae of few species been rec ognised. Evidences for competitive interactions among these essential fatty acids suggest that besides a minimum dietary requirement for each essentia l fatty acid, their relative ratios must also be considered.