The colouration is generally a mottled brown on the upper surface and sides above lateral line, with this pattern continuing over the head and snout.

The downstream distribution is unknown, but may have been more widespread in the past before the advent of introduced trout, which appear to have reduced and broken up its range.

[2] A wholly freshwater fish without a salt water phase in its lifecycle, G. brevissimus has only been found in one clear, open and gently flowing, small creek that was about 1 metre (3.3 ft) across and around 300 millimetres (12 in) deep.

[2] Breeding biology is unknown, however all adults examined during mid March were at an early stage of gonad development.

The smallest fish collected during this time, 49.4 millimetres (1.94 in), indicates a possible breeding season of late winter or early spring.