Reduced fish oil intake was also linked with decreased expression
of factors involved in hepatic proteasomal dependent proteolysis (proteasome-subunit alpha3 and ubiquitin protein ligase genes). This is indeed novel information providing support to the usefulness of the transcriptomic approach. Since the protein and carbohydrate intakes were similar, hepatic protein degradation can be ascribed only to the change in fat intake, leading to a reduced digestible energy. This consequently increases the use of amino acids as an energy source, a phenomenon well described in most teleosts (Dabrowsi and Guderley, 2002). Such a regulation of one nutrient metabolism by another has also been suggested in another study with trout showing that gluconeogenesis seems to be more efficiently regulated by dietary protein than by dietary carbohydrate (Kirchner et al., 2003). Given the high protein requirement of fish, there is definitely more need for understanding the role played by dietary amino acids in different metabolic pathways.