  We present the largest catalogue to date of optical counterparts for HI
radio-selected galaxies, Hopcat. Of the 4315 HI radio-detected sources from the
HI Parkes All Sky Survey (Hipass) catalogue, we find optical counterparts for
3618 (84%) galaxies. Of these, 1798 (42%) have confirmed optical velocities and
848 (20%) are single matches without confirmed velocities. Some galaxy matches
are members of galaxy groups. From these multiple galaxy matches, 714 (16%)
have confirmed optical velocities and a further 258 (6%) galaxies are without
confirmed velocities. For 481 (11%), multiple galaxies are present but no
single optical counterpart can be chosen and 216 (5%) have no obvious optical
galaxy present. Most of these 'blank fields' are in crowded fields along the
Galactic plane or have high extinctions.
  Isolated 'Dark galaxy' candidates are investigated using an extinction cut of
ABj < 1 mag and the blank fields category. Of the 3692 galaxies with an ABj
extinction < 1 mag, only 13 are also blank fields. Of these, 12 are eliminated
either with follow-up Parkes observations or are in crowded fields. The
remaining one has a low surface brightness optical counterpart. Hence, no
isolated optically dark galaxies have been found within the limits of the
Hipass survey.
