Requerimientos nutricionales en selenio y manganeso para los juveniles de dorada (Sparus aurata) alimentados con dietas prácticas con alto contenido de ingredientes vegetales

The present experiment was undertaken to establish the optimal dietary supplementation level of selenium (Se) and manganese (Mn) in gilthead seabream (GSB). Two experiments were done separately, one for Se and the other for Mn. In the first experiment, sodium selenite (Na2SeO3) was added to the practical dietes high in vegetable ingredients (Fish meal (FM): 10 per cent, Fish oil (FO): 6 per cent) to prepare five experimental diets with graded levels of Se (0.1, 0.2, 0.4, 0.7 and 1.1 mg Se kg-1 respectively). The high substitution levels of FM led to Mn levels in the basal diet, 20 mg Mn kg-1. Four other diets were supplemented with 0, 10, 16, 23 and 56 mg Mn kg-1 diet, supplied as manganese sulfate (MnSO4). Each trial was conducted with 450 fish, distributed into 15 tanks, and each diet was assigned to three replicate groups of GSB (initial body weight: 12.6 ± 1.5 g, mean ± SD) for 6 weeks. At the end of the trial, growth and productive parameters were monitored and samples were taken for biochemical, mineral and histological analyses. Growth in terms of weight was significantly improved by the inclusion of dietary Se up to 0.8 mg Se kg-1, whereas further supplementation reduced it. On the other hand, growth, productive parameters or survival were not significantly affected by dietary Mn supplements. Dietary Se and Mn supplementation did not significantly influenced protein and ash contents in whole body, but whole body lipid content was higher in fish fed 0.5 mg Se kg-1 Se diets and in fish fed 76 mg Mn kg−1 diets respectively. Se retention in liver increased with increasing Se supplementation, and Se concentrations in whole body responded linearly to supplemented Se, up to a level of 0.8 mg Mn kg−1 and then reached a plateau. However, Mn concentrations in whole body and vertebrae were significantly increased by dietary Mn supplementation and the Mn supplement did not have a significant effect on the concentration of Mn in the liver. Prevalence of steatosis in the liver of fish fed diets with lower dietary Se was significantly higher and decreased with the increase in Se in the diet. On the contrary, no significant differences of prevalence of steatosis in the liver were found in fish fed diets containing different levels of Mn. In summary, the optimal dietary Se requirement of GSB appears to be 0.8 mg Se kg-1, as denoted by the increased growth, Se retention and reduced prevalence of steatosis in the liver. Dietary Mn did not significantly affect growth of GSB. Vertebrae and whole body Mn increased readily with dietary Mn supplement