North-eastern Queensland, including the Wet Tropics and southern Cape York Peninsula is a biodiversity hotspot for Australian freshwater fishes. In particular, there are seven currently recognised rainbowfish taxa, and a likelihood of additional undescribed species. All but one of the rainbowfish taxa are either endemic to the region, or reach their southerly distribution limits in the region.

Although there are large tracts of protected areas in north-eastern Queensland, coastal lowland freshwater habitats are poorly represented and potentially vulnerable to disturbance. Analysis of habitat and distribution of rainbowfishes in the region based on historical records can be misleading due to past misidentifications, translocations and possibly localised extinctions. Further, some lowland rainbowfish species have specialised habitat requirements and highly fragmented distribution patterns.

This study examines the historic and current distribution of two coastal lowland rainbowfish species (Melanotaenia trifasciata and Cairnsichthys rhombosomoides) in the Wet Tropics and adjacent regions. The current fine scale distribution of these species was determined through field surveys and included documentation of sites and habitats, local extent of populations and the discovery of some new populations. The continued viability of some populations is of concern due to their small size and restricted habitat.