Shortjaw kokopu (Galaxias postvectis)

The shortjaw kokopu is probably the rarest of the whitebait galaxiids, although recent discoveries of several new populations lead us to believe it is more common than previously thought. It is usually found in streams with large boulders and is difficult to catch using conventional methods. The recent discoveries have mostly resulted from observations using torches at night when the fish move out of cover for feeding.

As its name implies, the shortjaw kokopu has an undercut jaw, with the lower jaw being shorter than the upper jaw. Koaro also have shortened lower jaws, but they are much more tube shaped than the kokopu. Shortjaw kokopu are also rather drab in colour unlike the sparkly koaro. Sometimes the fins of the shortjaw kokopu appear reddish-brown and there is a distinctive dark patch behind the gill openings. Otherwise, this fish is essentially brownish with faint bands and blotches.

Shortjaw kokopu are unique to New Zealand and do not occur on Stewart or Chatham Island. Although they penetrate well inland in many catchments, they appear to be restricted to streams with native forest vegetation. Because this fish has been so rarely encountered, little is known about its life history. Hopefully, the recently discovered populations will give us the opportunity to learn more about this member of the Galaxiidae family.