Marine lipids
supplied in equivalent amounts. This indicated a very low transfer efficiency between the artificial diet and the spat because these sterols are
usually assimilated at similar rates when they are only provided by
microalgae (Soudant et al., 1996, 1998). The low ingestion-accumulation
of the emulsion may be due to:
- the physical characteristics of emulsion, leading to a possible lower
acceptability than algae;
- a lower filtration efficiency due to particle size;
- a control mechanism of the free sterol absorption in the spat;
- loss due to possible emulsion adhesion to the tank.
Cholesterol accumulation by the spat was three times higher than stigmasterol, demonstrating selective incorporation of cholesterol. Such a
preferential incorporation of cholesterol over other sterols has been previously observed in P. maximus (Soudant et al., 1998). Bioconversions
of algal brassicasterol, campesterol or 24-methylenecholesterol in cholesterol could have also occurred. This may allow a sufficient level of
cholesterol for cellular regulation by the spats. Studies on biotransformation ancl de noro synthesis of sterols show contradictory results
(Walton & Pennock, 1972; Teshima & Patterson, 1981 ; Voogt, 1975;
Holden & Patterson, 1991). Some bivalve species have the ability of de
novo synthesis and/or modifying dietary sterols. But in most cases, synthetic ability was limited.
In conclusion, sterols appeared to be good markers for assessment of
ingestion-absorption of different diets. However, the relationship between
the ingestion-accumulation of these sterols and the other dietary components remains to be assessed. A concentration over 10% WW emulsion
per algal DW appeared to give substantial response in terms of nutrition
application. However, it has been observed in preliminary experiments
that emulsion concentrations over 1.6 mg WW/l resulted in perturbation of algal filtration. This is why we supplied the 20% dose twice a day
(1.25 mg WW/l at the time of the addition). For higher concentrations,
a continuous distribution of the emulsion may provide a compromise
between the low emulsion accumulation rate and a sufficient supply of
sterols for the spats. Increasing the emulsion sterol concentration, if
technically feasible, should also be considered as a way to improve the
yield of sterol transfer from artificial diet to oysters.
Acknowledgments
This material is based upon work supported by the European Commission under
grant FAIR CT. 96/1852, ‘Breeding improvement of Crassostrea gigas by nutritional and gametogenesis control’, and under Training Mobility Research grant FAIR
GT. 96/0762, ‘Contribution to study essential recjuirements for Crassmtrea gigas
broodstock using artificial complementation’.
Bibliographic references
Caers M., Coutteau P., Lombeida P., Sorgeloos P., 1998. The effect of
lipid supplementation on the growth and fatty acid composition of
Tapes phtlippinarum (L.) spat. Aquaculture, 162, 287-299.
128
supplied in equivalent amounts. This indicated a very low transfer efficiency between the artificial diet and the spat because these sterols are
usually assimilated at similar rates when they are only provided by
microalgae (Soudant et al., 1996, 1998). The low ingestion-accumulation
of the emulsion may be due to:
- the physical characteristics of emulsion, leading to a possible lower
acceptability than algae;
- a lower filtration efficiency due to particle size;
- a control mechanism of the free sterol absorption in the spat;
- loss due to possible emulsion adhesion to the tank.
Cholesterol accumulation by the spat was three times higher than stigmasterol, demonstrating selective incorporation of cholesterol. Such a
preferential incorporation of cholesterol over other sterols has been previously observed in P. maximus (Soudant et al., 1998). Bioconversions
of algal brassicasterol, campesterol or 24-methylenecholesterol in cholesterol could have also occurred. This may allow a sufficient level of
cholesterol for cellular regulation by the spats. Studies on biotransformation ancl de noro synthesis of sterols show contradictory results
(Walton & Pennock, 1972; Teshima & Patterson, 1981 ; Voogt, 1975;
Holden & Patterson, 1991). Some bivalve species have the ability of de
novo synthesis and/or modifying dietary sterols. But in most cases, synthetic ability was limited.
In conclusion, sterols appeared to be good markers for assessment of
ingestion-absorption of different diets. However, the relationship between
the ingestion-accumulation of these sterols and the other dietary components remains to be assessed. A concentration over 10% WW emulsion
per algal DW appeared to give substantial response in terms of nutrition
application. However, it has been observed in preliminary experiments
that emulsion concentrations over 1.6 mg WW/l resulted in perturbation of algal filtration. This is why we supplied the 20% dose twice a day
(1.25 mg WW/l at the time of the addition). For higher concentrations,
a continuous distribution of the emulsion may provide a compromise
between the low emulsion accumulation rate and a sufficient supply of
sterols for the spats. Increasing the emulsion sterol concentration, if
technically feasible, should also be considered as a way to improve the
yield of sterol transfer from artificial diet to oysters.
Acknowledgments
This material is based upon work supported by the European Commission under
grant FAIR CT. 96/1852, ‘Breeding improvement of Crassostrea gigas by nutritional and gametogenesis control’, and under Training Mobility Research grant FAIR
GT. 96/0762, ‘Contribution to study essential recjuirements for Crassmtrea gigas
broodstock using artificial complementation’.
Bibliographic references
Caers M., Coutteau P., Lombeida P., Sorgeloos P., 1998. The effect of
lipid supplementation on the growth and fatty acid composition of
Tapes phtlippinarum (L.) spat. Aquaculture, 162, 287-299.
128