Fisheries experts in the south-west are increasingly concerned about an unidentified disease in wild salmon off the coast.
Up to 300 fish have died so far in rivers, and preliminary findings have ruled out ulcerative dermal necrosis (UDN), a disease that involves a white fungus.
The mystery disease appears as a red linear patching underneath the skin on the salmon's underbelly.
It came to light when fishery officers were investigating cases of sunburn among fish in rivers. The officers found that fish with the combination of sunburnt backs, UDN and this new disease were dying within days.
First noticed in freshwater salmon, the red markings on the fish are now showing up on salmon in drift nets off the coast, according to Mr Aidan Barry, chief executive of the South Western Fisheries Board.
All staff in the Cork area have been involved in attempting to map the disease. Consultants have been brought in, and samples are now being taken from the Kerry coast.
Veterinary experts from the Marine Institute are to visit the south-west again in the next days to carry out further tests.
"It is worrying from our point of view in that we haven't seen this disease before," Mr Barry said.
The most affected area is the Ballycotton to Bantry coastline.
Mr John Lucey, the EPA representative on the fisheries board, has asked if affected, fish could go to market. Mr Barry said all the coastal fish were being sent to market. They looked perfectly healthy except for this slight patch of redness underneath the skin, and a virus was ruled out.
Yesterday, Mr Leo Foyle, of the department of veterinary pathology at UCD, said the patchiness could be a naturally occurring bacteria, or it could be markings made by lamprey eels.