Cairnsichthys is a small genus of rainbowfish (family Melanotaeniidae) restricted to rainforest streams of far northeastern Queensland, Australia - one of the narrowest ranges of any rainbowfish genus. The atlas covers 2 species, 2.5–3.5 in, sharing the compact, laterally compressed body and two separate dorsal fins typical of the family. Both known species come from short, fast-flowing coastal drainages near Cairns and the Daintree, rather than the broader inland river systems most Australian rainbowfish occupy.
This is a genus of real conservation concern rather than a mainstream aquarium staple: the atlas records one species as Critically Endangered and the other as Endangered, and one carries a CARES conservation priority listing here. C. rhombosomoides, the Cairns rainbowfish, is the better-established species among specialist rainbowfish keepers, while C. bitaeniatus, the Daintree rainbowfish, is rarer in the hobby and known from an especially small stream range - the kind of narrow-endemic pressure typical of northeastern Queensland's rainforest fish fauna, where land clearing and stream modification threaten habitat that these fish cannot simply relocate from.