The aim of this work was to gain insights into the muscle fibre phenotype and ultrastructure in blackspot seabream juveniles, a potential candidate for Portuguese aquaculture. Firstly, we used a panel of isoform-specific antibodies as well as histochemical staining for myosin ATPase and for SDH enzyme activity (a marker for mitochondrial content and oxidative metabolism) to identify myosin expression. Secondly, muscle fibre types were also identified by their fine structure where powerful approaches contributed to understand the muscle fibre phenotype of blackspot seabream juveniles. We observed that the main part of the musculature consisted of fast-white fibres, with a narrow strip of slow-red fibres situated superficially adjacent to the lateral line. A zone of intermediate-pink muscle fibres was inserted between those muscle domains (Fig.1).