  Ultra-compact dwarf galaxies (UCDs) are a new type of galaxy we have
discovered in the central region of the Fornax and Virgo clusters. Unresolved
in ground-based imaging, UCDs have spectra typical of old stellar systems.
Ninety-two have been found in Fornax, making them the most numerous galaxy type
in the cluster. Here we present multicolour (u'g'r'i'z') imaging of the central
region of the Fornax Cluster using the CTIO 4m Mosaic Telescope. The
colour-magnitude relation for bright UCDs is qualitatively consistent with UCDs
being the stripped nuclei of dE,Ns. However at faint magnitudes, GCs and UCDs
cannot be distinguished by colour alone. High resolution spectroscopy to
measure their internal velocity dispersions and metallicities, is needed to
distinguish between GCs and UCDs.
