In parasite news...

More than 90% of popular freshwater game fish in Southern California contain an introduced parasite capable of infecting humans, according to a new study by researchers at UC San Diego's Scripps Institution of Oceanography. 

The parasites found in the study—two species of flatworms called trematodes—typically cause gastrointestinal problems, weight loss or lethargy when they infect humans. In some rare and severe cases, the parasites have caused strokes or heart attacks.

The findings, published in the Journal of Infectious Diseases, suggest that these parasites pose a previously unrecognized public health risk in the United States.

"Americans don't usually think about parasites when they eat freshwater fish because it hasn't historically been an issue here," said Ryan Hechinger, an ecologist and parasitologist at Scripps and the study's senior author. "But these trematodes have now been widely introduced in the U.S. and that means that doctors and the public should be aware."

Hechinger emphasized that there is "no need to panic" as the risks posed by these parasites are easy to mitigate: Fully cooking fish or freezing any intended to be eaten raw for at least one week should kill the trematodes, per Food and Drug Administration guidelines. 

I wonder what the situation is with Australian freshwater fish?  Well, Google leads me to a recent article:

Australia has a highly endemic freshwater fish fauna, but basic biological knowledge for most is lacking. This includes an understanding, and description, of their parasite fauna. Additionally, the impacts of introduced fish species, and their parasites which have transferred across to native species, are also mostly unknown. This review provides the current level of knowledge of parasitic infection of the freshwater fish in Australia, both introduced and native. Only about a third of the native freshwater fish, but almost two-thirds of introduced fish, have been reported as a host for a parasite. The majority of records occur along the eastern coastline of Australia and throughout the Murray Darling Basin; two drainage regions were yet to record any parasite infections. Of the 124 fish species, across 43 families, found as hosts in Australia, only 11 species had more than 10 reports of infection, with 31% of fish species only having single reports. A total of 13 different types of parasites were reported, with digeneans, protozoans, nematodes and monogeneans the most commonly reported. Significant gaps in the knowledge of parasites, and their potential impacts, of Australian freshwater fish still exist, and the need for fish biologists and fish parasitologists to work together is highlighted to ensure that as much information about each group can be obtained.