Carp herpes virus could help reduce degradation of Logan, Albert river systems

An introduced herpes virus could be the solution to reducing the number of carp that are ravaging native aquatic life in the Logan and Albert Rivers.

Key points: Carp were first seen in the Logan and Albert rivers after the floods of 1974. Carp consume the vegetation of the native fish and affect their habitat. The koi herpesvirus can cause further problems within the ecosystems

Carp have survived well in most Australian waterways because they can tolerate extreme temperatures – from 4 degrees to 40 degrees Celsius.

They are native to Central Asia and were brought to Australia as a sport fish in the 1800s.

University of Queensland School of Biological Sciences researcher Andrew Barnes said carp were not picky eaters and could extract nutrients from sediment and algae.

“They tolerate little oxygen and require very little water, which means they are very successful in many freshwater environments and simply crowd out the local population by making better use of the available resources,” Professor Barnes said.

Carp can die within days of contracting the virus. (Credit: Cameron Atkins)

Logan and Albert Fish Management Association secretary Lloyd Willman told ABC Radio Brisbane’s Steve Austin the introduced pest species was first found in south-east Queensland river systems after the 1974 floods.

He said state and federal governments have been working on plans to activate the herpes virus without affecting the environment since the release of the National Carp Control Plan at the end of 2022.

“[Carp] are definitely in large numbers in the river,” said Mr Willman.

He said the virus that will be introduced is a common carp virus.

“It’s normally overtaken by the carp contacting each other, and then within a few days they die,” he said.

Impact on native species

Mr Willman and Dr Barnes said there were concerns about the introduction of the virus where the carp population is high.

“Most viruses and hosts adapt over time, so it’s not a sure-fire solution, and the carp herpes could very well become Murry River cod virus,” Dr Barnes said.

Dr Barnes says the introduction of carp herpes could affect native species. (Provided: Carp Frenzy Facebook)

“Natural systems are complicated, and you can’t replicate them in a test situation.”

Dr Barnes also said if the herpes virus was introduced, the carp could continue to affect the native fish after they died.

“In a localized area with a lot of carp, the virus would cause problems, as the dead carp would decay, and would decrease the water quality, lower the oxygen and increase ammonia, which is toxic in the water,” he said.

“This impact can remove many native fish and other aquatic animals from the drop in water quality.

“If the virus is introduced, the dead carp will have to be removed every day so they don’t continue to affect the native species.”

Success not guaranteed

Dr Barnes said viruses such as herpes killed the carp in different ways and although experiments in fish farms worked well, there was no guarantee of the success rate in the wild.

Dr Barnes says even the dead can negatively affect native wildlife. (Provided: Andrew Barnes)

He said the virus can burst the fish’s cells, suppress the immune system or weaken the animal enough that it becomes prey.

“While Koi herpesvirus has been quite nasty in experimental infection models and in fish farms, mortality rates in a natural outbreak can be quite low,” Dr Barnes said.

“This means that the effectiveness as a biocontrol agent may not be quite as good as hoped or expected.

“It cannot be predicted how quickly or how many fish the virus can kill in a natural system.

“There will be a whole lot of variables that will affect that.”

A spokesperson for Biosecurity Queensland said the National Carp Control Plan was a work in progress.

The spokesman said the plan suggests further work on a number of important issues before a decision is made on the release of the virus.

“This may include further research into the safety of the virus for non-carp species, regulatory approvals, agreements from all relevant jurisdictions and extensive consultation with stakeholders,” the spokesperson said.

They said the government would develop its response to the plan once the outstanding issues were addressed.

“The government in principle supports the use of biocontrol methods to manage invasive pests,” said the spokesperson.

Carp is a restricted harmful fish under the Biosecurity Act 2014 and must not be kept, fed, given away or released into the environment without a permit.

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