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Parasitic leech found off Kollam a likely threat to native fish health

KOLLAM: A parasitic marine leech previously found only along the Atlantic and Mediterranean coasts has been reported for the first time in Indian waters off the Kollam coast. The finding has raised concern among researchers about the parasites potential impact on fish health, fisheries productivity and the marine ecosystem. The species, Pontobdella muricata, was found among the trawl bycatch that landed at Sakthikulangara harbour. The specimen was found attached to the ventral side of a ray fish, confirming a new parasite-host association for a leech previously restricted to colder European waters. Researchers say the leech poses no direct threat to humans but warn that it could severely affect native fish populations. Even a single leech can cause lesions, draw blood and create wounds that allow secondary infections reducing fish health and market value, says the study. The finding has triggered concerns about what else may be silently shifting to Keralas waters. The current detection is limited to deepwater skates, but researchers warn that the shift in parasite distribution may indicate changing ocean conditions, altered migration routes or broader ecological imbalances. Our marine ecosystem is already under extreme stress due to global warming, pollution, deep-sea fishing and declining fish stocks. With fisheries under unprecedented pressure, the emergence of a new parasite is a red flag, said Sarlin Pathissery, head of the zoology department, Fatima Mata National College, Kollam, who led the study. The new parasite could harm fish populations in the long run, especially in waters already stressed by overfishing, warming seas and species degradation. But how exactly this will affect the fishing community and the wider environment requires in-depth study, she said. If such parasites spread to commercially important species, small fishers who depend on healthy, clean catch for their livelihood will be the most affected, the study notes. Impact of parasites may be huge, need further study The exceptionally high genetic similarity (more than 99%) between the Kollam specimen and populations from the Atlantic and Mediterranean coasts underscores the need for focused comparative assessments to determine whether similar ecological or pathological effects may arise in Indian waters. Researchers argue that monitoring such hidden parasites is crucial not just for biodiversity records but to understand subtle ecological shifts that ultimately influence coastal livelihoods. The discovery of the parasite is a reminder that what is hiding under the ocean will reach the market fish stall and our homes sooner than we expect. These parasites may be small, but their impact could be huge. Thats why further study is needed, said Sandie Moris, a chemical engineering student at Government Engineering College, Thrissur, who assisted the study. Savio Morris, chemical engeneering student at TKM Engineering College, Kollam, and Sancia Moris of the Fraunhofer Institute for Chemical Technology, Germany, were also part of the study. It has been published in a peer reviewed international journal, Taylor & Francis Biodiversity. First time in Indian waters Its for the first time that parasitic marine leech, Pontobdella muricata, is found in Indian waters, says the study The species was previously found only along the Atlantic and Mediterranean coasts The leech could severely affect native fish populations