Assimilation of dietary phytosterols by Pacific oyster Crassostrea gigas spat

Pacific oyster Crassostrea gigas spat were fed either the microalga Chaetoc eros muelleri, Isochyrsis aff. galbana (strain T-ISO) or Pavlova lutheri to investigate the effect of dietary phytosterols on the sterol composition o f spat tissues. After a 6-week feeding period the sterol profile of spat ti ssues generally reflected that of the diet, but not all sterols were assimi lated with the same efficiency. 4-Desmethyl sterols, such as cholesterol an d 24-methylcholesterol, were readily incorporated into spat tissues but 4-m ethyl sterols, such as 4-methyl-24-ethyl-5 alpha-cholest-22E-en-3 beta-ol a nd the unusual 3,4-dihydroxy 4-methyl sterol 24-methylpavlovol present in P . lutheri, were poorly assimilated by spat. The absolute content of every s terol decreased in spat that had been starved for 6 weeks, but the relative sterol composition was similar to the initial sterol profile. However, the relative level of cholesterol increased, indicating the important role of this sterol in spat metabolism.