Abstract
Gilthead sea bream Sparus aurata from consecutive year classes (0+ and 1+) and from the same parent stock were fed four diets, three of which were fortified with copper, iron and zinc. Concentrations of these elements were little affected by the diet. Hepatic, renal and splenic tissues sections were examined to detect the influence of the diet on the number and morphology of macrophage aggregates (MAs); in particular their structure was examined in the spleen. Three different types of MAs were detected: (1) unstructured, (2) partially structured and scarcely defined and (3) fully structured and well defined. Melanin was the most abundant pigment in the pigmented macrophages which form MAs and the amount of this pigment was influenced by season. Ferritin, in contrast with previous data obtained in other fish species, was more abundant in renal than in splenic MAs. Significant differences in splenic MA numbers among fish fed different diets and among different periods of the year were detected. The results suggest that a polyfactorial regulation could act on the splenic MA number in gilthead sea bream.