Anglers and fishery owners are asked to be on the lookout for salmon showing signs of bleeding and skin ulcers.
Small numbers of salmon affected have been found in at least six rivers throughout the country.
It follows reports of salmon also returning to Norway and Scotland with a red rash skin disease in recent months.
Dr Paddy Gargan, senior research officer at Inland Fisheries Ireland, says the reason for what’s happening is unclear.
He has this advice for people who see or catch such salmon:
