In salmonids, esterified astaxanthin was found to be less efficiently deposited than unesterified astaxanthin (Storebakken et al., 1987). Choubert and Heinrich (1993) indicated that the cleavage of the astaxanthin esters might be a limiting step for the pigmentation, which resulted in lower carotenoid retention in rainbow trout by H. pluvialis than by synthetic astaxanthin (Sommer et al., 1991).