Because of the large variability in colour pattern found within S. decorus (types with rounded spots) including its synonym S. vittatus (types with longitudinal bands), a detailed morphometric study has been undertaken including 27 measurements and two counts of 68 specimens. We distinguished three different colour pattern types: banded , spotted and uniform . Banded specimens were found only in the Upper Congo (i.e. above the Wagenia rapids at Kisangani), spotted specimens only in the Lower and Middle Congo (i.e. below the Wagenia rapids). Uniform specimens were rare and only found in the Middle Congo. In the Uele River exceptionally only uniform specimens were found. Although multivariate analyses demonstrated a weak morphometric difference between the banded specimens on the one hand and the spotted and uniform specimens on the other, none of the measurements revealed to be significantly different between colour pattern types. Our results thus confirm the synonymy of S. vittatus with S. decorus. During this study, we found a striking resemblance in colour pattern between small S. decorus and S. nummifer specimens. However the latter lack the typical branched maxillary barbels of S. decorus and the horizontal black band in-between the two caudal-fin lobes. The latter feature is typical for S. decorus at all sizes. Moreover, as reported by Poll (1971), the number of mandibulary teeth is larger, 12 (rarely 8) to 19, in S. nummifer (vs. 0 to 10 in S. decorus). Finally, while S. decorus has 2 to 4 vertical dark brown/black bands in the caudal fin regardless of size, in S. nummifer this number increases with size, with larger specimens having approximately 7-8 bands.