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Reared meagre (Argyrosomus regius) of average weight 1278 g was evaluated for its filleting yield and fillet lipid quality. Filleting yield averaged 42.2%, while very low levels of muscle fat deposits were measured (1.06%). Analysis of lipid classes revealed a high proportion of polar lipids (48.3-59.1%) and low levels of neutral fatty acids (40.9-51.7%) when compared to corresponding values of other farmed fish species. Phosphatidyl-choline (PC) was the dominant polar lipid (2.92 mg g )1 muscle), while cholesterol the most abundant neutral lipid (1.68 mg g )1 muscle). The fatty acid composition of meagre fillet generally reflects the dietary fatty acids. Among n-3 fatty acids, eicosapentaenoic (4.58%) and docohexaenoic (15.0%) were measured to be the most abundant ones, and 18:2n-6 (11.9%) was the most common n-6 fatty acid. The fatty acid profiles of polar and neutral fractions differ, with monounsaturated fatty acids being predominant in the neutral and n-3 polyunsaturates in the polar lipids. The high polar lipid contents and n-3 fatty acids and the low atherogenic and thrombogenic indexes indicate a high quality of this species' lipids.

An experiment was conducted to evaluate the effects of dietary composition on apparent digestibility coefficients of protein, fat and carbohydrate of gilthead sea bream. In addition α‐amylase and proteolytic activities were measured in the digestive tract of fish, held at 20±1°C. Six experimental diets were formulated containing approximately 40%, 45% and 50% protein, 11% and 21% fat and a starch level which fluctuated from 14% to 36%. Fish having an average weight of 100–130 g were used, fed at 1.5% of their body weight daily, and digestibility was measured using an indirect method. Enzyme activities were measured in the digestive tract of fish, fed diets containing a combination of 40%, 50% protein with 11%, 21% fat at 0.5, 5, 10, 24 h after a single meal. Starch digestibility was reduced with its level in the diet. It also negatively affected fat digestibility as well as protein digestibility, the last only at the high fat level. Dietary fat level had a negative effect on starch and protein digestibility. Fat affected also strongly α‐amylase levels in the digestive tract, while its effect on protease activity was of smaller magnitude. These results indicate that digestive enzyme activities and nutrient digestibility values are affected by dietary composition, carbohydrates and fat indicating the strongest effect.

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