Scientists at Croatia’s Ruđer Bošković Institute (IRB) have become the first in the world to decode the genes of Dentitruncus truttae, a little-known intestinal parasite found in trout in the Krka River, identifying gene sequences that could help monitor and mitigate heavy metal pollution in freshwater ecosystems, a press release from the IRB said.

The research team, led by scientists from the IRB’s Division for Marine and Environmental Research, published their findings this week in Scientific Reports, part of the Nature portfolio. Their study is the first transcriptomic analysis of an acanthocephalan parasite, a group of organisms known for their ability to accumulate toxic metals such as lead, mercury and cadmium.

“This parasite doesn’t have a mouth or a digestive tract, yet it can absorb high levels of toxic metals through the gut wall of its fish host,” said lead author Sara Šariri, a PhD candidate at the IRB. “We’ve now begun to uncover the genetic mechanisms that make this possible.”

By sequencing the parasite’s transcriptome — the set of all active genes — the scientists identified more than 1,900 proteins that bind metals such as zinc, copper, iron and nickel. These proteins, including a high number of zinc-finger proteins known for regulating gene expression, may help the parasite cope with environmental stress and detoxify heavy metals.

The findings suggest that D. truttae not only survives in contaminated waters but may also offer protective benefits to its fish host. Previous research by the team showed that trout infected with acanthocephalans had lower concentrations of toxic metals in their tissues compared to uninfected fish.

“This raises fascinating ecological questions,” said Dr. Tatjana Mijošek Pavin, co-author of the study, according to the press release. “Could these parasites actually be shielding their hosts from metal exposure? And could they serve as natural indicators of pollution in freshwater systems?”

Until now, genetic data had been published for only one of the approximately 1,300 known acanthocephalan species. The breakthrough by the Croatian researchers opens the door for new biomonitoring tools, including molecular tests that could use parasite gene expression to assess pollution levels in rivers and lakes.

“Our work provides a foundation for developing new environmental monitoring methods based on parasite biology,” said Dr. Vlatka Filipović Marijić, a co-author of the study. “At a time when freshwater ecosystems are under increasing pressure from pollution and climate change, we need all the tools we can get.”

The team said further research is needed to confirm the detoxifying role of the parasite, but their findings highlight an unlikely ally in the fight against environmental degradation.

“This organism has evolved to thrive in conditions that are toxic to most others,” said Dr. Irena Vardić Smrzlić, who heads IRB’s Laboratory for Aquaculture and Pathology of Aquatic Organisms. “Understanding how it does this could transform the way we think about parasites—not just as threats, but as potential partners in conservation.”