The gastrointestinal microbiota of fish is characterized by its high population density, wide diversity and complexity of interactions. Importantly, GI microbes have a profound influence on nutritional, physiological and immunological processes in the host. Recently, findings from culture-based methods have been supplemented with molecular ecology techniques that are based on the 16S rRNA gene. These techniques enable characterization and quantification of the microbiota, and also provide a classific...