As with other types of animals, there is a great diversity of freshwater fish in the Wet Tropics. 78 of Australia's 190 species occur here. One of the most common families is the rainbow fish which is found throughout the area, except around Cape Tribulation. Another widely distributed small fish is the Pacific blue-eye. Larger species found in the coastal reaches of Wet Tropics rivers include jungle perch, catfish, sooty grunter and mangrove jack - all popular among recreational anglers. The numbers of endemic fish (species that occur nowhere else) are surprisingly low. Only eight Wet Tropics endemic species have been identified so far, but this could change radically if more taxonomic work is done.
The streams of this area contain many barriers to fish migration (such as waterfalls at one end and saltwater at the other) so that many upland watercourses have been isolated for a long time. Such isolation often leads to a high level of endemism, at least to the subspecies level if not the species level. Unfortunately, there haven't been many studies of northern fish apart from those with a demonstrated commercial or recreational value.
For example, the small rainbow fishes and gudgeons haven't received much attention. As more taxonomic and DNA studies are completed, we will probably see many more uniquely Wet Tropics subspecies and possibly species being confirmed, bringing the endemism levels for our freshwater fish into line with other types of animals.
Many fish species seen on the Great Barrier Reef as adults actually started their lives in streams and brackish water estuaries (mixed fresh and saltwater). The reverse also takes place with some freshwater fish migrating to saltwater to breed. The freshwater rivers and streams of the Wet Tropics also support a myriad of fauna in addition to fish such as platypus, crayfish, aquatic insects, frog and tadpoles, terrestrial insect larvae, shrimp and even some marine species.
You can read all about freshwater fish and other freshwater fauna in the 2012 - 2013 Annual report and State of Wet Tropics Report [3MB]. The State of the Wet Tropics report describes in detail aquatic habitats, biodiversity and water resources in the Wet Tropics.