Freshwater Fish - The Lake Eacham Rainbowfish Story

This fish is the subject of a truly amazing story, the final chapters of which have yet to be written. Several rainbowfish are present throughout various parts of the Wet Tropics but the Lake Eacham inhabitant in particular has a strange history.

Lake Eacham is actually a volcanic crater which has 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 Rainbowfish (Melanotaenia eachamensis) - which is very similar to the Eastern Rainbowfish - found its way into the volcanic lake. Unfortunately for the small species, other larger native fish were introduced into this closed system and eventually, these larger fish ate the Lake Eacham Rainbowfish 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. It actually came to pass that these private collections became the source stock to reintroduce the fish to the lake. However, the cause of the species' demise was still living in the lake and proceeded to eat up the entire population of introduced stock. But the story doesn't end there.

Fish researchers working in the Wet Tropics rivers and streams have found the Lake Eacham Rainbowfish in the Tully, Herbert and Johnstone Rivers and Dirran Creek. But the plot thickens … some of them are the genetically pure version that used to occupy the 'closed' Lake Eacham but others are hybrids caused by interbreeding with the Eastern Rainbowfish.

It's hard to predict where the next chapter will lead. Because of the complete infestation of Lake Eacham by translocated native fish from other water systems, it is futile to continue restocking the lake with rainbowfish. Getting rid of the predatory species is a major problem and a solution which is non-destructive to the species that belong in the lake is not going to be found in a hurry. The moral of this story is that the translocation of fish, even native ones, is a really bad idea that can create irreversible problems.