Lipid nutrition of marine fish during early development: current status and future directions

Research on the dietary requirements of marine fish larvae has evolved from considerations of optimal dietary levels of n - 3 HUFA to considerations of optimal dietary ratios of the two principal HUFAs, 22:6n - 3 and 20:5n - 3, and more recently to considerations of optimal dietary levels and ratios of all three dietary essential fatty acids, 22:6n - 3, 20:5n - 3 and 20:4n - 6. Our present understanding of the requirements and optimal dietary balance of 22:6n - 3, 20:5n - 3 and 20:4n - 6 is reviewed. Limitations of enriching live feed are considered, particularly from the point of view of achieving an optimal balance between levels of phospholipids and triacylglycerols in enriched live feeds that generate an optimal blend of essential fatty acids and energy-yielding fatty acids. It is concluded that the ideal marine fish larval diet is one containing circa 10% of the dry weight as n - 3 HUFA-rich, marine phospholipids with less than 5% triacylglycerols, as exemplified by the lipid compositions of marine fish egg yolk, marine fish larvae themselves and their natural zooplankton prey. Such diets provide 22:6n - 3, 20:5n - 3 and 20:4n - 6 in the desired levels and ratios and simultaneously satisfy known requirements for phospholipids, inositol and choline. Approaches to developing marine fish larval diets more closely resembling this "gold standard" diet are considered. (C) 1999 Elsevier Science B.V. All rights reserved.