Optimising
lipid nutrition in first-feeding flatfish larvae
J.G. Bell, L.A. McEvoy, A. Estevez, R.J. Shields,
J.R. Sargent
Aquaculture, 227(1-4): 211-220
Abstract:
Although global production of flatfish has increased
in recent years, both in terms of numbers of fish and diversification into
new species, problems still remain with low survival rates and difficulties
with metamorphosis. This short review highlights some advances made in
optimising lipid nutrition in an attempt to overcome some of these problems.
Copepod nauplii are the best live prey for first-feeding flatfish larvae.
Rotifers can provide a useful method of essential fatty acid delivery but Artemia
are poorer in this regard, especially at first feeding. Copepods are
nutritionally beneficial due to their naturally high levels of the essential
highly unsaturated fatty acids (HUFA), 20:5n-3 (eicosapentaenoic acid; EPA)
and 22:6n-3 (docosahexaenoic acid; DHA), which are predominantly in the form
of phospholipids. Rotifers can be enriched with fish oil emulsions to
provide compositions similar to copepods, while enriched Artemia are
difficult to enrich with high levels of DHA and the HUFA tend to be located
in triglycerides rather than phospholipids. There is considerable evidence
that the superior efficacy of copepods and rotifers is largely due to the
digestibility and availability of HUFA supplied as pre-formed phospholipids.
In addition to the essentiality of EPA and DHA, the requirement for 20:4n-6
(arachidonic acid; ARA) should also be considered. Improvements in dorsal
pigmentation in turbot and halibut can be achieved by providing ratios of
DHA/EPA of >2:1 but, perhaps more importantly, an EPA/ARA ratio of
>5:1. This suggests that eicosanoids are involved in the control of
pigmentation and this is further supported by the use of enrichments
containing 18:3n-6, the elongation product of which (20:3n-6), is a potent
inhibitor of ARA-derived eicosanoid formation, as is EPA.
(Institute of Aquaculture, University of Stirling,
Stirling FK9 4LA, Scotland, UK, e-mail: g.j.bell@stir.ac.uk)