FEATURE - Australian freshwater fish as unique as kangaroos
SYDNEY - Just when you thought you knew all the weird and wonderful creatures of Australia, along come the hibernating salamander fish, the stinging scorpion fish, and a lung fish that breathes but once an hour.
As aquatic oddities, the unique species bubbling up from down under are particularly interesting to scientists, because they appear on one of the driest continents on the planet.
\"Most of it is unique... There are some fantastic things that in their own right are every bit as special as kangaroos and koalas,\" fish scientist Gerald Allen told Reuters. Allen, together with co-authors Hamar Midgley and son Mark Allen, has collected decades of work in a new book: \"Field Guide to the Freshwater Fishes of Australia\", published by the Western Australian Museum and the government-backed Commonwealth Scientific and Industrial Research Organisation (CSIRO).
In contrast with the great variety of marine fish which teem off Australia\'s coasts, the country has one of the smallest number of inland freshwater fish species anywhere - the result of the arid nature of the Australian continent.
But the 300 species of freshwater fish which do exist in Australia are mostly unique and are most sensitively tuned to the harsh continent\'s environment, Allen\'s work shows.
The \"very special\" salamander fish, which usually grows to only 4.5 centimetres long and looks a little like a dark grub with fins and tail, is found only in pools in a tiny patch of sandy coastal scrubland on Australia\'s far southwestern tip.
MYSTERY SOLVED BY WATER TRUCK
The fish posed a mystery for years. It disappeared when pools dried up in summer, then magically re-appeared next year.
To try and solve the puzzle, Allen borrowed a water truck from the local council one hot summer to flood a dried-up hole.
\"It was just amazing. Within 10 or 15 minutes the pool was virtually teeming with fish,\" he said.
The experiment showed the salamanders protect their ancient lineage from extinction by burying themselves in the mud for a summer-long hibernation.
Each fish usually lives only a year, but awakens from its summer sleep in time to spawn when the rain arrives.
\"It\'s very finely tuned for the arid environment in which it lives,\" Allen said.
The Queensland lungfish is another example of an Australian rarity, even though other types of lungfish exist elsewhere.
Found only in a coastal pocket of central Queensland, the fish has existed virtually unchanged for 150 million years, an ancient contemporary of dinosaurs.
Even Allen is baffled by what makes the fish, which breathes air at the surface once or twice an hour to supplement its oxygen supply, such a successful survivor.
\"Sharks, you can understand. They\'re the ultimate predator,\" Allen said. \"But as far as lungfishes go, I\'m fascinated. I don\'t claim to fully understand (why they have survived so long).\"
POISONOUS SCORPION FISH
Allen has also found two blind cave fish that live in the perpetual darkness of subterranean water around the Exmouth area of Western Australia.
One is a colourless gudgeon which reaches a maximum size of about five centimetres, the other a cave eel which reaches a maximum 40 centimetres and looks like a long pink worm.
Neither have skin pigment or eyes, but have well developed sensory systems to detect vibrations in their dark world.
\"It seems pretty amazing that with all the underground cave terrain found in Australia, there really aren\'t any specialised cave fishes except for these two in a tiny corner of Western Australia,\" Allen said.
Then there are rainbow fish, a small, colourful group which inhabit a variety of waters from clear, fast-flowing streams to small mudholes and are unique natives of Australia and Papua New Guinea.
These days the prolific breeders are also found in aquariums around the world through now-banned exports.
TOUGH AT HOME, FRAIL ABROAD
The common thread among Australia\'s unique freshwater fish is survival responses to an arid land.
\"They tend to be like people on this continent. Most are clustered around the coastal fringes,\" Allen said.
They are so finely attuned to harsh conditions that most will remain uniquely Australian - or die.
\"It points out just how fragile many of our species are in terms of hanging in there. If anything happens to that habitat, they\'re gone. And there\'s so little of that habitat,\" Allen said.
Of Australia\'s 300 species of freshwater fish, about 100 are estuary fish that swim in both marine and freshwater systems. That leaves about 200 truly freshwater fish.
There are no man-eaters among Australia\'s freshwater fishes.
But there are nasties, including the bullrout, the world\'s only freshwater species of scorpion fish.
\"You wouldn\'t want to step on one of these,\" Allen said.
Story by Michael Byrnes
REUTERS NEWS SERVICE
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