A feeding trial was conducted to determine the sparing effect of lipids on dietary protein in gilthead sea bream Sparus aurata fingerlings, by combining different levels of protein (42-58%) at two lipid lev els (9, 15%) in the diets. Sardine meal and sardine oil were employed as the main source of dietary pro tein and lipid, respectively. Weight gain and specific growth rate of fish improved for each dietary pro tein level when lipids were increased in diets from 9% to 15%, up to 52% dietary protein. There was evi dence of a protein sparing effect of dietary lipid, as evident by a reduction of dietary protein from 52 to 46%, and an increase of dietary lipid from 9 to 15% in diets resulting in slightly better fish growth. There were no significant effects on the protein efficiency ratio. The increase of dietary lipid produced an increase in body lipid deposition, both in visceral and non-visceral tissues.

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The effects of varying dietary protein level on several nutritional parameters of Sparus aurata fry were studied. Seven approximately isoenergetic diets were formulated with protein levels ranging from 35% to 65%. in increments of 5%.Highest specific growth rates were obtained in fish fed 55% protein at a fixed dietary feeding rate of 6% body weight per day, being significantly different from the other fish groups. Feed efficiency was sig nificantly higher with diets containing the highest protein levels, when compared with dietary levels be low 45%. Protein efficiency ratio values showed a trend towards an increase up to a maximum with 55% dietary protein, whereas carcass composition was only slightly affected. The minimum dietary pro tein level producing maximum growth of S. aurata fry was found to be 55%.

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