Experts say fish carrying a parasite that turns their flesh into mush could be travelling further south in New South Wales as sightings become more common around Sydney.
Species affected by the microscopic parasites include kingfish, mackerel and mahi mahi.
Craig McGill is a professional fishing guide on Sydney Harbour and says he has recently caught more kingfish with the parasite in waters off Sydney.
“It’s really prominent this year,” he said.
“I’ve caught more in the last two seasons than I have in 30 years combined fishing.”
Mr McGill said there were no tell-tale signs a fish had the parasite when it was caught, but it became obvious when it was cooked.
“As soon as you put the heat on the flesh, it just goes to liquid,” he said.
“Best-case scenario, it’s like mash-potato consistency. Worst case [you can get] a bag of fluid.”
Diagnostic test in the works
There are several types of parasites that can infect various fish: One (kudoa) can turn the infected fish to mush once it is killed. Another (Unicapsula seriolae) liquefies the fish once cooked.
The Fisheries Research and Development Corporation (FRDC) said it was expected to sign a contract with RMIT University to create a rapid diagnostic test to identify whether a fish had the parasite.
If successful, the test would be used on yellowtail kingfish and mahi mahi to help Australian fishers avoid serving a plate of liquid fish.
Dr Julien Pepperell, a Queensland-based researcher and independent marine biologist, said the parasite was effectively trying to escape the dead host.
“When the kingfish is killed, and especially when it is cooked, the little parasite is still alive and it tries to escape the host by liquefying the muscle around it,” he said.
“But in doing so, the flesh of the fish turns mushy.”
Mushy fish syndrome, as it is known, has been documented in northern New South Wales and southern Queensland waters.
The first detection of the parasite in Australia was near Brisbane in 1982.
Jessica Bolin, a University of the Sunshine Coast joint PhD candidate in marine ecology, said it was “entirely plausible” the parasites were moving further south to Sydney.
“[They could be] hitching a ride on the east Australian current, but we need more baseline information,” she said.
Kudoa parasites have been found in several fish species right around the world, including countries such as Japan, Norway and Canada.
According to experts, there is no evidence in Australia of side effects to humans from eating kingfish or mahi mahi infected with the parasite.
“If you ingest or eat the parasite, you’re not going to get sick from it,” Ms Bolin said.
Researchers are calling for citizen scientists to record and report any fish they catch that are found to have the parasite.
