• Anglers in Australia and New Zealand are being asked to help Charles Sturt University research to improve understanding of the spread of parasite-infected ‘mushy fish’
• Fish can be infected with a suspected parasite (a microscopic Cnidarian) which are known to cause flesh altering conditions among other fish species world-wide
• Evidence suggests the prevalence of infections is on the rise under climate change

A new Charles Sturt University research project based in Port Macquarie seeks the help of anglers around Australia and New Zealand to improve our understanding of the spread of the ‘mushy fish’ issue.

Lecturer in Ecology Dr Jessica Tout-Lyon (pictured inset above) in the Charles Sturt School of Agricultural, Environment and Veterinary Sciences in Port Macquarie and the Charles Sturt Gulbali Research Institute of Agriculture, Water and Environment is the lead researcher of the Mushy Fish Project.

“Imagine tucking into a freshly caught Yellowtail Kingfish (Seriola lalandi) which is highly prized for sashimi and sushi only for it to crumble and have the texture of wet newspaper,” Dr Tout-Lyon said.

“This issue has been close to my heart for more than 15-years and last year was by far the worst year I’ve experienced with the abundance of mushy fish caught along the mid north coast of NSW.

“Caught in waters along the New South Wales coast, these fish can be infected with a suspected parasite (a microscopic Cnidarian - think corals and jellyfish) and this group of parasites are known to cause flesh altering conditions among other fish species worldwide, and in some cases can even result in food-borne illnesses.

“The prevalence of infections appears to be on the rise due to climate change and is becoming a familiar issue facing anglers in and around Sydney and further south.”

The first documented case of infected Kingfish in Australia was in 1982 off the coast of Brisbane, through the work of Bob Lester. Since then, species distributions are expanding, resulting in range-shifts and the issue is now found throughout NSW waters.

Dr Tout-Lyon said infected fish are indistinguishable from those not harbouring the parasite when live or dead.

When prepared and eaten raw as sashimi, infected fish appear exactly like un-infected fish; the flesh smells, tastes and looks the same.

It remains unknown whether the parasite affects human health, but anecdotal reports and her own experience indicate any ill-effects remain hidden.

“Cooking, smoking or preparing as ceviche is the only method to confirm parasite presence in Kingfish,” she said.

“The parasite releases an enzyme resulting in tissue disintegration leading to the familiar ‘mushy flesh’ and rendering the fish unpalatable.

“This results in a lower market value for commercial fishers, wasted effort for recreational anglers, an unpalatable dinner for consumers, and a wasted product overall. It is absolutely devastating taking the life of an animal only to find out later that night, it cannot be eaten.

“Even thinking creatively about how to use the flesh of an infected fish, such as in fish cakes, isn’t a great option as the texture has been lost, and some dogs have been known to turn their nose up at the infected fish.

“But if you eat the same fish raw as sashimi, it is still beautiful, and you have absolutely no idea it is a ‘mushy fish’.”

She said Mahi Mahi or Dolphin fish (Coryphaena hippurus) are also known to suffer from mushy flesh, but this species presents a little differently to infected Kingfish and suffer from post-mortem myoliquification, or essentially, can turn to jelly in the esky.

“There have been several reports and videos posted on social media in the last two weeks documenting these beautiful fish just turning to paste in the esky,” Dr Tout-Lyon said.

“Again, it is tragic that this happens to both the fish and the angler alike.”

In addition, many anglers throughout NSW waters have also reported other species of fish with similar issues.

Dr Tout-Lyon asks fishers that when they catch a mushy fish to log it on the research project’s website with its story map and click on the embedded survey, or follow the survey link or QR code. No download or login required.

“This data will help us better understand the spread of this issue along our coast, and you don’t need to be in NSW, we welcome fishers from all over Australia and New Zealand,” Dr Tout-Lyon said.

“To improve our understanding of the spread of the mushy fish issue in Australia, we seek the help of anglers ─ line fishers, spearfishers, First Nations cultural fishers, commercial or recreational fishers ─ to log their mushy fish catches.

“The last documented evidence was recorded in 1982, so it is important to collect new information so we know if the parasite is spreading, how far it has travelled and whether anglers elsewhere will soon be facing a similar issue.”

Dr Tout-Lyon said the research team has been busy this year conducting preliminary investigations into this issue in waters along the mid north coast of NSW and in Sydney Harbour with anglers donating both fish tissue and water samples so we can detect if the parasite is present.

Results from this preliminary study are promising as they have validated molecular tools to identify the parasite and have also found the parasite appears to be present in fish that don’t present as mushy at all.

“This points to a more complex issue and interaction than we originally thought, and I’ll be relying on the continued efforts of the passionate Kingfish fishing community Australia-wide to help unravel the mushy fish mystery,” she said.

If anglers would like to contribute fish tissue samples or water samples to the project, please get in touch with Dr Tout-Lyon by emailing jetout@csu.edu.au