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Scientists tackle costly parasite damage devastating fish farmers around the world

At the heart of the Amazon, researchers are investigating a mysterious parasite which is devastating fish farms around the world.

Parasites called myxozoa infect fish populations with deadly diseases, leading to severe losses in types of fish including salmon and trout. This loss of fish stock costs the fishing industry more than £50 million annually worldwide.

In the Amazon basin, home to one of the greatest diversities of fish, an international team of scientists led by King's College London and Universidade Federal de São Paulo (UNIFESP) have found more than 50% of all fish examined are infected by parasites. This threatens the livelihood of fish farmers, alongside biodiversity and recreational fishing. Elsewhere, some streams in the western United States have lost 90% of their trout due to parasitic infection.

To find out more about these parasites, the team from King's, UNIFESP, Federal University of Western Pará Brazil, University of Zagreb Croatia, University of Cambridge and Natural History Museum London set up a lab on a boat traveling along the Amazon basin in Brazil where the Tapajós and Amazon rivers converge, close to the city of Santarém, State of Pará. The paper is in the journal GigaScience.

They hope that investigating the different ways the parasites control their genes could hold the key to understanding the parasite and devising treatments.

Professor Paul Long, expert in marine biotechnology, Faculty of Life Sciences & Medicine, King's College London, said, "We work in the Amazon because the diversity of life in the Amazon basin is undisputed and still little-known. This is especially true when it comes to parasites, which are hidden inside their hosts.

"Knowledge of parasites is fundamentally important for understanding the tree of life. How parasites co-evolve with their hosts and these complex relationships will influence biodiversity as well as ecosystem structure and function.

"To our surprise we uncovered a new process of gene regulation that was previously believed not to exist in these parasites. Fish farming is a key contributor to global food security. Understanding how genes are turned on and off opens the opportunity to develop gene-based vaccines to control these economically significant fish pathogens.

Professor Edson Adriano, a parasitology expert from the Department of Ecology and Evolutionary Biology-UNIFESP, said, "The vast Amazon basin is home to the largest diversity of freshwater fish in the world. This makes it a perfect setting to study fish parasites.

"Our discoveries about epigenetic processes in myxozoans open new avenues for understanding how the distinct conditions encountered by the parasite throughout its life cycle can affect genetic regulation. This becomes even more important when considering the impact scenarios predicted by climate change."

Dr. Santiago Benites de Pádua, a veterinarian and manager of Brazilian Fish Company, added, "Studies on these parasites are essential for developing strategies to control or reduce their impact on the health of farmed fish."