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The possible influence of the feeding regime (FR) on the immune system and pathological status of gilthead sea bream was studied. Two growth trials were performed starting at different seasons (trial 1 = March; trial 2 = June) under controlled experimental conditions. In both trials, FR-1 groups received a restricted amount of food, whereas FR-2 groups were fed to visual satiety. The pathology study included parasitological and bacteriological examination, and the immunological traits analysed were respiratory burst activity of head kidney leucocytes, serum lysozyme and alternative pathway complement activity (ACH50). The immunological status of gilthead sea bream not only was not impaired by the restricted feeding regime, but also seemed to be enhanced in some aspects, as the respiratory burst of FR-1 fish of trial 2 was significantly higher. No differences in the bacterial isolates were detected between the two feeding regimes, and Vibrio harveyi was the most prevalent species in both cases, especially in warm months. Also, fish under FR-1 regimes had significantly lower mortality, lower prevalence of infection of all the parasites except Cryptosporidium molnari, and less histopathological alterations in liver and intestine than those under FR-2 regimes. © 2003 Elsevier Science B.V. All rights reserved., This work was supported by research grants from the Spanish Ministerio de Educación, Cultura y Deporte under FEDER Program no. 1FD97-979-C02. M. Mingarro was recipient of a fellowship from the Diputación de Castellón. We are thankful to M.L. Alonso, M.A. González and G. Sanza for technical assistance in the samplings, and to J. Montfort for the histological processing.