Growth and nitrogen metabolism of sea bass fed graded level of nucleic acid nitrogen from yeast or RNA extract as partial substitute for protein nitrogen from fish meal

Some studies carried out in mammalian models have shown de novo synthesis and salvage of nucleotides to be a costly metabolic process and a dietary supplementation with nucleic acids (NA) or nucleotides has been suggested to result in a protein sparing action (Sanderson and He, 1994). On the other hand, high levels of dietary NA could have toxic effects and lead to disturbance in protein, lipid and carbohydrate metabolism in monogastric animals lacking uricase activity, an enzyme involved in NA degradation (Clifford and Story, 1976). So far, there is no clear indication of such effects in fish fed nucleic acid-enriched diets (Tacon and Cooke, 1980; Rumsey et al., 1992; Fournier et al., 2002). The aim of this experiment was to investigate growth response and N metabolism in juvenile sea bass (D. labrax) fed diets supplying graded levels of nucleic acid N from dry brewer's yeast or RNA extract as partial substitutes for protein nitrogen provided by fish meal.