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Why you should never put a goldfish in a park pond … or down the toilet

Goldfish might look nice, but they can also spread a variety of decidedly not-nice viruses. kaori/pixabay.com

Why you should never put a goldfish in a park pond … or down the toilet

Have you ever walked past a fountain in the park and seen beautifully coloured fish swimming about, and wondered how they got there? Often with the best of intentions, people leave unwanted pet fish in public fountains, ponds and natural waterways for a variety of reasons, including boredom with their pet, moving house, or frequent illness in their fish.

But these places are not a natural home for ornamental fish, and they can harm Australia’s unique ecosystems.

Fish are very popular pets, for good reason. They take up very little space or time and can add a calming presence to any living room. But fish come with the same responsibilities as any other pet. Much as (I hope) you wouldn’t turn a dog or cat loose to fend for itself in the local area, there is no place for pet fish in our waterways.

Alien fish species harm our ecosystems

Rehoming pet fish in natural waterways causes two big issues. The first is that most fish kept as pets are not naturally found in Australia, so releasing them means introducing an alien species into the wild.

These alien fish are pests and can outcompete native fish for shelter, food and other resources. Australia has 34 alien freshwater fish species living in the wild, two-thirds of which are ornamental fish such as goldfish, cichlids, guppies and gourami. Once an alien fish species becomes established, it is impossible to get rid of it.

Better left indoors: a dwarf gourami. Jvarszegi/Wikimedia Commons

The second problem is the inadvertent release of exotic diseases. Australia imports 19 million ornamental fish every year – almost one per person! Your pet might appear healthy, but it can carry exotic bacteria and viruses.

When introduced to a new waterway, these pathogens can potentially wipe out entire populations of native fish. What’s more, many unique Australian fish such as Murray cod and Macquarie perch are particularly sensitive to exotic pathogens.

Unsurprisingly, Australia has strict import conditions for ornamental fish (and other pets too). However, there have been two key cases of exotic viruses hitchhiking with imported pet fish.

Goldfish get herpes too!

The first involves a disease called herpesviral haematopoietic necrosis, which affects only goldfish. It is caused by the virus Cyprinid herpesvirus 2 (CyHV2), first isolated in 1992 in Japan after a spate of goldfish deaths. Since then, CyHV2 has caused large goldfish kills in Taiwan, the United States and Britain, and it is now present in Australia. It is not known how long a goldfish can spread the virus once it becomes infected.

You never know what’s under the surface. aussiegall/Wikimedia Commons, CC BY

Before 2010, CyHV2 was considered exotic to Australia and all imported goldfish were required to be certified as free of the virus. Despite this, in 2008 sick goldfish from several pet shops in Sydney tested positive for it. Pet shops stock a mix of imported and domestic fish, so the source of infection was unknown.

To try to trace the source of the virus, my colleagues and I have tested goldfish from farms across Australia and in wild populations. We found CyHV2 at two farms, one in Victoria and one in New South Wales. More importantly, the virus was found in wild goldfish collected from Cotter Reservoir, ACT, and the Ovens and Murray River in Victoria.

Our results confirmed that CyHV2 was present in both domestically farmed and wild goldfish populations. The virus is now considered an established pathogen in Australia, and in 2011 the Department of Agriculture dropped the requirement for goldfish to be certified free of CyHV2 before entering the country.

Goldfish were first introduced to Australia in 1876 and have long been established in all states except the Northern Territory. Although we can’t be sure when the introduction of CyHV2 occurred, it is assumed to have been within the past two decades.

Once established, pathogens like this are almost impossible to eradicate. The good news is that CyHV2 infects only goldfish, which is an alien species and is not vital to our ecosystems.

Lessons learned

The second case involves a pathogen called infectious spleen and necrosis virus (ISKNV). This belongs to a group of viruses called the megalocytiviruses, notorious for killing large numbers of fish farmed for human consumption as well as ornamental fish. ISKNV kills Murray cod, and our soon-to-be-published research suggests it can also cause disease in Macquarie perch and Golden perch.

Research has identified imported ornamental fish infected with ISKNV both before and after quarantine. Infected fish have also been found at pet shops and at a fish farm in Queensland. However, all the ornamental fish collected from the wild tested negative for the virus. From March 2016 onwards, regulations for imported fish have been tightened to clamp down on this virus.

ISKNV is still considered exotic to Australia. To protect Australia’s biodiversity and aquaculture industries, changes to importing ornamental fish were introduced from March 2016. This shows how, with the right monitoring, exotic pathogens can be spotted and dealt with before they become established in the wild.

Caring for your fish – and the environment

Like any pet, the decision to bring a pet fish home should be made with the care and thoughtful consideration that is owed to these beautiful creatures. If you can no longer care for your pet fish, the best choice is to find another living room for it to enjoy. Alternatively, you can take it to your veterinarian who can kill it humanely. If your fish has died, throw it in the rubbish bin, not down the toilet!

Ornamental fish are devastating to our natural waterways. Greater awareness of responsible pet fish ownership could have avoided alien species establishing themselves in the wild and prevented death and disease among Australia’s native fish.

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