Invasive walking fish threatens Australia


A fish that can live out of water for up to six days and crawl across dry land is being closely watched by scientists as it moves towards Australia.

The aggressive Climbing perch has already overrun Australia’s two most northerly outposts – the Torres Strait islands of Boigu and Saibai – respectively just four and six kilometres south of the Papua New Guinea mainland.

Dr Nathan Waltham of James Cook University said it would now prove very difficult to eradicate from the two islands, despite only being first officially recorded there in late 2005.

He said there was also now evidence the freshwater fish could tolerate exposure to saltwater. "It does seem to be able to handle a little bit of salt. In our trip up there in December we found it in some hyper-saline water holes, so there is some ability to resist exposure."

The fish drags itself from waterhole to waterhole and is very invasive, outcompeting native species once it is established in a new environment. It is extremely hardy, and has been known to hibernate in the mud of dried-up creek beds for up to six months. It has been witnessed swelling up when swallowed by larger predators, blocking their throats so they either choke or starve.

Dr Waltham said the perch may have come to Boigu and Saibai on a surge of fresh water from flooding rivers in the nearby Papua New Guinea mainland. But its ability to live in saltwater was a concern, in terms of it moving closer to Cape York and becoming established in mainland Australia.

"I still think the chances of it getting to Australia by swimming are quite low," said Dr Waltham. "There is more chance it will arrive in the bottom of a fishing boat or as discarded live-bait fish."

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