Blackspot seabream (Pagellus bogaraveo) fed different diets. Histologic study of the lipid muscle fiber distribution and effect on quality during shelf life

Abstract

To determine differences between commercial size wild and farmed blackspot seabream, some parameters affecting quality were evaluated during shelf life, namely the fatty acid profiles, pH, muscle colour and Quality Index Method (QIM). In addition, a histological study of the lipids' distribution in the myotome (slow or fast twitch) in different dorsal areas was performed. In farmed fish, three diets were tested. One of them was a commercial diet formulated with a high proportion of lipids, mostly from fish oil. The other two diets were formulated with reduced lipid levels by 60%. In one (low lipid diet, LL) the proportions of protein sources were maintained and in the other (low lipid diet+fish meal, LL+) most of the protein was provided as fish meal.Lipid depots were not found to be different in the myocytes of the fast-twitch fibers. However, regional differences were identified in the slow-twitch fibers depending on the area and the diet, whether in the cranial, medial or caudal portion of the dorsal myotome. The worst scores of the QIM were recorded for the Control diet and the wild fish group. In addition, QIM showed a positive correlation with total n-3 and a negative with other lipid fractions. The a* values in skin and the chroma in muscle of the wild fish were superior to those measured in farmed fish. Fish fed the LL+ diet had higher fillet protein content than that of the wild counterpart. As for nutritional value, farmed fish were able to deposit more DHA than was offered in all experimental diets used, especially with the LL+ diet which yielded threefold more DHA.