acids. This could have been related to the small size of the liposomes vs. an emulsion. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Fatty acid; Lipid; Emulsion; Liposomes; Oyster; Crassostrea gigas
1. Introduction
Unlike in fish and shrimp lipid nutrition studies, where the use of formulated diets allows the preparation of diets with a specific amount of virtually all important fatty
acids, bivalve studies are mainly performed by feeding different algal diets selected on the basis of their species-dependent fatty acid composition. Although fatty acid composi-
tions of algae can be modified by altering culture conditions, nutritional studies are
Ž compromised by this approach relative to formulated diets
Enright et al., 1986; .
Thompson and Harrison, 1992; Thompson et al., 1993 . Bivalve nutrition studies have Ž
. mainly focussed on n y 3 polyunsaturated fatty acids PUFA whereas the n y 6 PUFA
have received very little attention. Moreover, with a few exceptions, they only report the impact of the diet on the fatty acid composition of the total lipids. However, considering
Ž .
Ž the different function of the polar mainly structural phospholipids and neutral mainly
. storage triglycerides lipids, it is important to consider both lipid fractions.
Compared to emulsions, liposomes have the advantage that they can be used as an encapsulation technique for lipid as well as water-soluble components. We opted to use
the pro-liposome technique since pro-liposomes are a stable product that can easily be transported and the conversion into discrete liposomes and the loading with active
Ž .
ingredients can be carried out locally using simple equipment Arnaud, 1993 . There- fore, the pro-liposome technique holds promise for application in laboratory as well as
commercial hatcheries. Although pro-liposomes have been successfully used to enrich Ž
. Artemia with vitamin C Merchie, 1995 , they have not been used for bivalves.
Ž .
In the present study, lipid emulsions were used to supply n y 6 18:2 n y 6 and Ž
. Ž
. n y 3 PUFA 22:6 n y 3 to an algal diet Tetraselmis suecica containing only 2.6
18:2 n y 6 and no 22:6 n y 3. The fatty acids 18:2 n y 6 and 22:6 n y 3 were supplied as liposomes or emulsions and the partitioning of these fatty acids between the polar and
Ž .
neutral lipids of Crassostrea gigas Thunberg spat were followed. Additionally, the efficiency of emulsions and liposomes as fatty acid carriers for C. gigas spat were
Ž compared. Previous studies indicated that ethyl esters of docosahexaenoic acid DHA,
. 22:6 n y 3 can be used to illustrate the digestion and assimilation of lipid supplements
since 22:6 n y 3, supplied as ethyl esters, was clearly accumulated by larvae, spat and Ž
adults of various bivalve species Coutteau et al., 1994, 1996; Caers et al., 1998, .
Ž .
1999a,c . Therefore, pro-liposomes based on soybean phosphatidylcholine and emul- Ž
. sions based on soybean triglycerides were enriched with 22:6 n y 3 ethyl esters.
2. Materials and methods
