This species has only been recorded from the Thee and Noordhoeks Rivers, both small tributaries of the Clanwilliam Olifants river in the Western Cape, South Africa. It is extremely uncommon in these two streams it inhabits. A. barnardi inhabits riffles among loosely bedded rocks and coarse sand. Other species that occur in this area include Pseudobarbus phlegethon, Barbus calidus, and Austroglanis gilli. The reproduction of this species is unknown.
These fish reach a length of about 8 centimetres (3 in) SL. The head is flattened, the snout is broad, and the mouth is subterminal (downturned). There are three pairs of barbels. Their color is golden-brown with dark brown blotches.
A. barnardi is threatened by habitat destruction from several causes associated with agricultural development, including stream channelisation, water abstraction, and sedimentation, all of which reduce the incidence of their obligate riffle habitat. They are also threatened by introduced predators. Introduced plants may have an extensive effect on their habitat.