The roundhead galaxias is another non-diadromous member of the Galaxiidae family that is found only in Otago. It occurs in the Taieri and Clutha catchments, although there is still some uncertainty about the records in the Pomahaka. The map shows our best knowledge of its distribution to date and the description below refers to the Taieri roundhead galaxias.
The number of caudal fin rays can be used to distinguish the roundhead galaxias (16 fin rays) from the dusky (14 fin rays) and Eldons galaxias (15 fin rays), both of which also occur in the Taieri River catchment. The roundhead galaxias, flathead galaxias and koaro all have 16 caudal fin rays, and distinguishing characteristics for these species rely on the teeth, colour pattern, and shape of the head. Although roundheads are only known to co-exist with flathead galaxias in a single stream, and roundheads have never been found with koaro, positive identification is probably best left to the experts.
Roundhead galaxias grow to a maximum size of about 130 mm, but are rarely found larger than 90 mm long. They occupy a diverse range of low gradient streams, from small weedy drains to braided cobble streams. The roundhead is tolerant of high water temperatures and low flows, surviving droughts by living in remnant pools that remain in ephemeral streams. They spawn in early spring, laying their eggs amongst loose gravel and cobbles in riffles and at the stream edge. Spawning sites are used by many fish, and up to 40 individuals can be found at once in areas smaller than 10 x 10 cm.