Growth performance and product quality of meagre (Argyrosomus regius) fed diets of different protein/lipid levels at industrial scale

The rearing of meagre (Argyrosomus regius) up to commercial sizes, using diets of different protein/lipid ratios, was examined in two long-term trials. In the first 2 x 2 trial, four diets containing two protein (43% and 47%) and two lipid levels (15% and 20%) were evaluated in fish of 350 g initial weight. Fish were reared for 8 months in triplicate experimental cages, up to final weight of 900g. Growth performance showed that diets containing 43% protein were the most appropriate, as indicated by the better thermal growth coefficient (TGC): 0.70 and 0.71 (vs. 0.61 and 0.53 for 47/15 and 47/20 diets) and better daily growth index DGI: 0.91 and 1.00 (vs. 0.88 and 0.79 for 47/15 and 47/20, respectively). Liver fat did not differ among groups, but liver glycogen in the 43/15 dietary group was found to be significantly higher than the 47/20 (3.89% vs 1.88%). The histological examinations revealed a trend for increased lipid deposition when fish were fed high fat diets. Diets that performed best, namely 43/15 and 43/20, were used in a second trial conducted at a commercial fish farm. Fish weighing 520g were reared for 7 months up to 1100 g final weight. No significant differences were observed in the growth parameters examined. The feed conversion ratio was found to be better in the 43/20 diet compared to the 43/15 (1.58 vs. 1.68, respectively). The dietary fat levels significantly affected fillet fat content. However, such difference in nutritional content was not reflected in human-perceived sensory differences.