Fish & Shellfish Immunology (1999) 9, 637–640 Article No. fsim.1999.0219 Available online at http://www.idealibrary.com on SHORT COMMUNICATION Diet related changes in non-specific immune response of European sea bass (Dicentrarchus labrax L.) ARIADNA SITJA v -BOBADILLA AND JAUME PE u REZ-SA u NCHEZ* Instituto de Acuicultura de Torre la Sal (CSIC), 12595 Ribera de Cabanes, Castellón, Spain (Received 5 January 1999, accepted 22 March 1999) Key words: European sea bass, Teleostei, dietary lipids, health status, Myxosporea. The state of immunocompetence is a sensitive indicator of nutritional status, and it is now accepted that both nutritional deficiencies and excesses compromise immune response and disease resistance of mammals (Chandra, 1993). Research in fish species has been mainly focused on ascorbic acid, vitamin E and protein requirements (Blazer, 1992; Kiron, 1995). The immunosuppressive e#ect of dietary deficiencies in essential fatty acids (n-3 HUFA) has also been documented (Montero et al., 1998), but fewer studies link adiposity and dietary lipid content with health status. Experimental evidence indicates that the use of high energy diets (lipid enriched diets) in aqua- culture practice increases the amount of body lipid stores, and endocrine changes are accomplished to maintain adiposity at a regulated level (Martí-Palanca et al., 1996; Company et al., 1999a). The aim of the present study was to evaluate the e#ects of two laboratory diets with varying protein (55 v. 46%) and lipid (9 v. 17%) levels on some non-specific immune parameters, and the parasite burden of European sea bass (Dicentrarchus labrax L.). Data on growth performance and metabolic-endocrine status has been presented in a previous work (Company et al., 1996b). Fish with an average body weight of 11 g were distributed into 150 l tanks in groups of 30. Water temperature ranged from 23–26 C over the course of the trial (7 weeks, July–September). Each diet was randomly allocated to duplicate groups, and fish were fed to visual satiety three times a day. At the end of the feeding trial, fish were killed for parasitological examination and primary culture of head kidney phagocytes. The presence of Ceratomyxa spp. stages was determined in fresh smears of bile and gall bladder, the target tissues of these myxosporea (Sitjà-Bobadilla & Alvarez-Pellitero, 1993), and the infection rate evaluated as described previously (Alvarez-Pellitero & Sitjà-Bobadilla, 1993). No other parasites were found in the experimental animals, and no signs of bacterial infections were observed. The production of superoxide anion by phagocytes was measured by the NBT method, following the procedure described by Mun ˜ oz et al. (1998). Serum samples were stored at 30 C for 8 months until lysozyme and protein determinations were made. Lysozyme activity in serum was measured using a turbidimetric assay according to Ellis (1990), adapted to 96 well microplates. Serum total protein was measured by a Bio-Rad protein assay based on the Bradford dye-binding procedure (Bradford, 1976). The results showed that some parameters of immunological significance were modified by diet composition. Thus, following phorbol myristate acetate (PMA) *Corresponding author. E-mail:jperez@iats.csic.es 637 1050–4648/99/080637+04 $30.00/0  1999 Academic Press