'Monster' goldfish measuring more than half a metre caught in suburban Perth lake

A "monster" goldfish thought to be one of the longest ever caught has been reeled in from a suburban lake in Perth.

The fish, measuring 52 centimetres, was captured by aquatic biologist Dr Dulana Herath in Blue Lake Park in Joondalup, in Perth's north.

The creature is part of a growing goldfish problem taking over the city's waterways, mostly caused by people dumping unwanted pets.

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"Yeah, he was a monster," Herath told 9News.

Part of the reason the fish are growing so big is because there are abundant resources in the waterways, and the issue is so widespread even small ponds are home to many big fish.

"There's a lot of food resources here, so you've got tadpoles, you've got plants, soft-body plants which they'll feed on, you've got ample amount of space," Herath added. 

But feral fish are disrupting the natural ecosystem by taking up these resources

"Goldfish and carp have a feeding habit where they cruise along the bottom and basically mumble through the sediment, and that stirs it up and they'll eat anything they can get their mouths around in the sediment of the lake," Dr Stephen Beatty from Murdoch University explained.

To try and combat the issue, hundreds of fish were pulled out of Blue Park Lake during a three-day exercise, including the "monster".

It measured nearly five centimetres longer than the current Guinness World Record holder, a 47.4-centimetre fish caught in the Netherlands in 2003.

However, the Perth catch will not make it into record books due to the fact it has already been euthanised.

There are sometimes stories in the global media about other giant goldfish being caught, which perhaps also failed to register as a Guinness World Record for similar reasons.