Goldfish could use estuaries as ‘saltbridge’ to spread between rivers

September 19, 2017

River raider: Goldfish could be using estuaries as a 'saltbridge' to access new waterways (Pic by Mark Allen)

River raider: Goldfish could be using estuaries as a 'saltbridge' to access new waterways (Pic by Mark Allen)

Goldfish invaders have been discovered in Australian estuaries, meaning they can tolerate salty water and can potentially use it to move between river systems.

The latest discovery by Murdoch University researchers has major implications for the management and control of this invasive species.

A research team led by Dr James Tweedley from the Centre for Fish and Fisheries Research, made the alarming finding while conducting fish surveys in the Vasse and Wonnerup estuaries near Busselton in south west Western Australia.

Dr Tweedley said the invasive goldfish are vigorous feeders, uprooting and consuming vegetation, silting up waterways and releasing harmful nutrients into the water.

Last year, the scientists discovered goldfish that had grown as big as footballs – 40cm long and weighing more than two kilograms – were stalking the waterways.

In the latest research, across three surveys, a total of 526 goldfish were caught in the Vasse estuary, which is connected to its Wonnerup counterpart in wet winters by Malbup Creek.

This year, for the first time, goldfish have also been caught from the Wonnerup estuary, the researchers say.

Goldfish have been caught frequently and in large numbers by Murdoch researchers from the Lower Vasse River since 2003.

“This research indicates that goldfish could start using estuaries as a ‘saltbridge’ to invade and colonise new river systems,” said Dr Tweedley.

“Goldfish have been recorded in estuaries elsewhere around the world, but they have been confined to the uppermost parts of those systems or their presence has coincided with periods of high freshwater flows associated with heavy rains.

“However, we discovered the goldfish in the Vasse Estuary in the middle of summer. This is before it becomes very salty, but clearly the fish are capable of tolerating saline conditions for several months.

“This raises the concerning possibility that goldfish might use the estuary to access and expand its distribution into new waterways, such as the Sabina, Abba and Ludlow rivers.

“The reports of goldfish in the Wonnerup estuary are especially concerning as it seems to indicate their raids are already happening.

“The invaders may even exacerbate the regular algal blooms that occur in the system, and goldfish are a known vector for the introduction of parasites and diseases,” he added.

“This is bad news for native fish species and the overall health of our precious estuary and river systems.”

Often flushed down the toilet or released into waterways as an unwanted pet, goldfish love breeding conditions in the Vasse River.

Dr Tweedley said it was important that unwanted goldfish are returned to reputable aquariums rather than released into rivers.

“Our waterways are unique, helping to enhance our health and wellbeing, and we should try to do all we can to protect them,” added Dr Tweedley.

A paper on the research has been published online in the International Aquatic Research journal and can be viewed here.

The research was supported by the South West Catchments Council and the Department of Water.

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