Australia was once partially covered by an inland sea and during this time, many of the Wet Tropics fish arrived from elsewhere. When the sea receded, these species became isolated in northern rivers and streams and continued their evolution independently. One such isolated relic species is found only in the Bloomfield River.The Bloomfield River cod (Guyu wujalwujalensis) is very ancient and very rare and its survival may be due to the fact that a similarly sized species with a similar diet, the sooty grunter, does not exist upstream of the falls in the Bloomfield River. Were the sooty grunter (Hephaestus fuliginosus) or other large predatory fish to be translocated (deliberately or otherwise) into the Bloomfield River upstream of Wujal Wujal Falls, it might spell the end of the Bloomfield River cod, a species which has been around for roughly 60 million years!
This fish has a truly amazing story of extinction and survival. Several rainbow fish are present throughout various parts of the Wet Tropics but the Lake Eacham rainbow fish (Melanotaenia eachamensis) was found only in one place.
Lake Eacham is a volcanic crater which filled with water and is isolated from any other watercourse (making it an enclosed catchment). How any fish arrived there to begin with is a mystery in itself, but somehow the Lake Eacham rainbow fish, which is very similar to the eastern rainbow fish, found its way there. Unfortunately for the small species, other larger native fish like mouth almighty were introduced into this closed system and eventually, these larger fish ate the Lake Eacham rainbow fish into extinction - well, at least as far as the lake was concerned.
As it turned out, hobbyists had been collecting the fish from the Lake Eacham National Park (illegally) and were very successful at breeding them. These private collections were used to restock the lake, but of course the new fish were eaten too.
However, since then researchers have found what looked like Lake Eacham rainbow fish in the Tully, Herbert and Johnstone Rivers and Dirran Creek. Some of them were genetically identical to the Lake Eacham rainbow fish, while others had interbred with the eastern rainbow fish. We don't know how long they have been there.
The barramundi (Lates calcarifer) is one of the most well-known fish in Australia. Barra are the stuff that anglers dream of. They are the perfect sporting catch, lovely to eat and plenty of meat at a maximum of 60kg. The demand for this fish has sparked a multi-million dollar aquaculture and commercial fishing industry. However, it can be an aggressive predator of endemic species if translocated into upland areas which are not its native habitat..
Sometimes, the best things come in small packages. Tiny Gertrude's blue-eye (Pseudomugil gertrudae) is one such small package. Only 30mm long, this pretty fish has rows of spots along its side and throughout the dorsal, anal and tail fins. It prefers water bodies that are densely vegetated and swamps and lagoons are a favourite. As there is tremendous pressure to develop many of the north Queensland coastal wetlands, the Gertrude's blue-eye will be a species to keep a watch over to ensure that it doesn't become a newcomer to the threatened species list.
Found in some of the most unexpected places, the spotted eel is capable of moving over moist ground to get to other bodies of water. It also manages to climb up what would seem like impossibly high barriers such as weirs and waterfalls. This eel can be found in just about any watercourse in the Wet Tropics, including high altitude rainforest streams. The spotted eel (Anguilla reinhardtii), also sometimes called the long-finned eel, is pale or light brown with greenish spots over its upper body. Usually seen at about one metre in length, they can reach more than two metres and weigh over 16kg and are more thickset than exotic eels. This eel is curious and will come to the water's surface to have a look at you!
The life cycle of the eel is very different to most fish. Wet Tropics eels spawn in the Coral Sea and migrate as planktonic leptocephali to near-shore waters where they metamorphose as unpigmented glass-eels. They move into estuaries and then migrate upstream in response to floodwaters, to grow and develop through to small, fully pigmented elvers. Generally, the elvers which penetrate further upstream ultimately become females and grow to a larger size than males. Those which develop into males remain in estuaries and the lower reaches of streams. Sexually mature 'silver-eels' undergo marked changes in appearance and physiology and undertake a once-only downstream migration to the spawning grounds, where it is believed they spawn and die.
For more information about the impacts of fish translocations you can see: