We know Australia has a range of unique and endemic freshwater species – but how much do we actually know about the parasites they might carry?

Recently, a parasite known as Eustrongylides excisus or more commonly red-worm-of-trout, was found outside its known distribution range. This is cause for concern as this particular parasite can spread to other mammals which eat uncooked or undercooked fish, including humans. Professor Shokoofeh Shamsi, a parasitologist at Charles Sturt University, says there needs to be research on exactly how far spread the parasite is.

Keep in mind this is just one type of parasite. Australia's freshwater fish host a diverse array of parasites, yet our understanding of this relationship is somewhat limited. An article published in 2023 entitled, "Freshwater fish as hosts for parasites in Australia: How much do we really know?", looked to examine the host-parasite relationships in Australian freshwater fish. The study was published in Ecology of Freshwater Fish and revealed sizable gaps in knowledge that have critical implications for both fish health and ecosystem management.

Key findings

Host-Parasite Diversity

There is a high level of diversity in the parasites found in Australian freshwater fish, but the distribution of these parasites across different fish species is uneven. Of the 124 fish species included in the study, only a few had extensive documentation on parasitic infections, while many had very limited data. There is a significant lack of detailed studies on the parasitic fauna of many fish species. This gap poses challenges for managing fish health and conservation efforts effectively. Additionally, the lack of detailed information complicates efforts to understand the full impact of parasitic infections on both individual species and broader aquatic ecosystems.

Human Health Risks

Some parasites found in Australian freshwater fish pose direct risks to human health. For instance, the aforementioned Eustrongylides excisus has been detected in several native fish species, including Murray cod and galaxiids. This parasite can infect humans if they consume undercooked fish containing the larvae. The consequences of such infections can be severe, as the parasite can burrow into human tissue, leading to painful and potentially life-threatening conditions. This highlights the importance of public awareness and education on the risks associated with consuming undercooked or raw freshwater fish.

Invasive Parasites

The introduction of non-native parasites further complicates the management of freshwater ecosystems in Australia. One prominent example is the Asian fish tapeworm (Schyzocotyle acheilognathi), which has established itself in various water bodies across the continent. This invasive parasite is highly successful in colonising new environments and poses significant risks to native fish populations. It can lead to severe health issues in infected fish, including weight loss, reduced growth rates, and increased mortality. The presence of such invasive species underscores the importance of robust biosecurity measures to prevent further introductions and to manage existing infestations effectively.

Conclusion

Ultimately, the article calls for increased research and monitoring efforts to address the significant gaps in our understanding of freshwater fish parasites in Australia. Comprehensive studies are needed to document the full range of parasitic infections across different fish species and geographic regions. This information is crucial for developing effective management strategies to mitigate the impacts of parasitic infections on fish populations and to protect human health.

The authors emphasize the importance of involving parasitologists in environmental health and biosecurity efforts. Their expertise is essential for accurately identifying parasites, understanding their life cycles, and assessing their impacts on host species. Enhanced collaboration between researchers, government agencies, and industry stakeholders is needed to develop and implement effective biosecurity protocols that can prevent the introduction and spread of invasive parasites.

Full article available here.