The effects of various dietary protein levels on growth performance, whole body composition and nutrient utilization were studied in two-banded sea bream (Diplodus vulgaris), a candidate species for aquaculture. Fish (initial weight 6.1 g) were fed to satiety six iso-energetic diets, containing 5%, 12.5%, 25%, 35%, 45% or 55% of crude protein during 72 days. Fish fed 35% and 45% protein attained better growth and feed utilization than the other groups (P < 0.05). Daily growth index and feed conversion ratio were the poorest for fish fed 5% and 12.5% protein (P < 0.001), while the 25% and 55% protein groups had intermediate performance. Lipid retention increased significantly from 13.7% to 30.1% (P < 0.0001) and protein retention decreased from 35.5% to 21.3% (P < 0.01) with increasing protein levels from 12.5% to 45%. Muscle protein, lipid and energy concentrations were not significantly affected by dietary protein level. The estimated protein requirement for maintenance and maximum growth of two-banded seabream growing from 6 to 20 g were 7.5% and 35.7%, respectively. Protein requirements as calculated from body protein gain were 2.3 and 6.5 g of protein intake per kilogram body weight per day. KEY WORDS

a b s t r a c tThe quality of gilthead sea bream from distinct production systems and geographical locations in Southern Europe was evaluated to differentiate aquaculture products from extensive, integrated and semi-intensive systems from the ones produced intensively. This work analysed the external appearance of fish, yields after filleting as well as nutritional, sensory and histological characteristics of the muscle. The results showed that the yellow-golden line between eyes and the shiny red spot on the gill cover can be important and easy criteria to discriminate aquaculture products. Trimming losses are higher in fish from intensive systems. Lipid content of fish from extensive systems was significantly lower than values observed for fish reared intensively. Samples from the integrated and extensive systems showed the best n-3/n-6 ratio, contrarily to intensive systems, but it is difficult to establish clear quality markers to differentiate gilthead sea bream according to the rearing system. Regarding sensory characteristics, the sea bream flesh from intensive systems seems firmer and denser, having smaller white fibres and higher density of fibres in the dorsal muscle. The taste and odour of fatty fish was less strong in fish reared in non-intensive conditions, but extensive rearing in earthen pond is more propitious to the development of certain characteristics related to the environment.

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This study compared the effects of dietary l‐carnitine and ploidy on growth performances and fatty acid content in rainbow trout (Oncorhynchus mykiss). Fish [initial body weight (BW) = 30 g] reared under high density (50 kg biomass m−3) were hand‐fed in triplicate (3 tanks treatment−1, 34 fish tank−1) twice a day, with three nutritionally identical diets containing 15, 200 or 530 mg l‐carnitine kg−1 of diet. No significant growth differences were observed over a 56‐day grow‐out period, during which BWs increased threefold. Growth performances and survival were not significantly affected by either ploidy or dietary l‐carnitine content, although daily growth index showed an increasing trend (2.52–2.65% day−1) with increasing dietary l‐carnitine. Body l‐carnitine content increased significantly with dietary l‐carnitine content. Diploid fish had higher plasma ammonia (716–725 μmol L−1) and osmolality (297–303 mOsm) levels than triploid trout (523–649 μmol L−1 and 285–291 mOsm, respectively). l‐carnitine, ploidy and their interaction showed to affect significantly the concentration of several fatty acids. Palmitoleic (16:1), oleic (18:1) and erucic (22:1) acids showed lower concentrations, while the eicosadienoic (20:2n‐6) and arachidonic (20:4n‐6) acids were elevated in liver of triploid fish. Eicosapentaenoic acid (22:5n‐3) was significantly higher in fish fed 200 mg than in fish fed 15 mg l‐carnitine.

a b s t r a c tThis study describes the variability of important quality traits in gilthead sea bream produced under intensive conditions in Southern Europe and purchased in a French market (Nantes). Chemical, sensory and histological characteristics were performed on 18 samples delivered over a year. All fish presented far lower dioxin and DL-PCBs or heavy metals concentrations than the maximum limit level set by EC Regulation, being totally safe for human consumption. Fat content and nutritional values reflected by n-3 and n-6 polyunsaturated fatty acids (PUFA) levels were parameters with high variability according to the season or the fish farm. Values of n-3 PUFA ranged from 0.9% to 8.6% and those of n-6 PUFA from 9.3% to 16.6%, corresponding to a respective variation of n-3/n-6 ratio between 0.1 and 0.6. Increased fat levels in flesh lead to a more intense odour, a fatty fish flavour and a whiter appearance of the cooked fillet. Flesh total amino acid composition was rather stable whereas the small differences detected on firmness by the sensory panel were weakly related to histological characteristics. Rearing techniques of the farm seems to modulate the major characteristics of the fish.