In this study, we report a deeply sequenced metatranscriptome from the anterior part of gilthead sea bream intestinal mucus with three objectives: i) to study and characterize the full set of microbes present in the gut of this fish species, ii) to evaluate if genetic background and alternative diets can change the expression of genes collectively expressed by these microbial communities, and iii) to unravel which metabolic processes are enriched in gilthead sea bream gut and which microbial community is involved. Overall, this work aimed to provide more insights into the broad microbial landscape of gilthead sea bream intestine to make a positive impact in its health and farming in aquaculture.