The Southern Regional Fisheries Board has ordered a full scientific survey into a serious outbreak of a fungal disease which may have affected up to 10 per cent of wild salmon stocks on the Blackwater river.
The disease was confirmed this week as ulcerative dermal necrosis (UDN), and is the first such outbreak among salmon stocks in the State in 34 years. Ironically, the condition is partly caused by overpopulation of fish, indicating that wild salmon stocks are plentiful.
A board spokesman said an estimated 500 to 600 fish may have died on the river below Fermoy as a result of the outbreak. It is conducting a survey with UCC to assess the extent of the outbreak.
The Minister for the Marine and Natural Resources, Dr Woods, has requested daily updates from the fisheries board, and has said he is fully supportive of the board's efforts.
UDN is a disease found in salmon, sea trout and occasionally brown trout, which manifests itself as lesions infected with white fungus on the back of the fish's head. It poses no danger to human health, but may spread to other fish.
The white fungal patches make the fish very visible in rivers as they move upstream or when they congregate in pools. However, the white fungal coating may not appear for some time after the infected salmon have entered freshwater. The fungal action spreads the lesion, and the condition proves fatal.
There is no definitive explanation for the cause of UDN, but three common factors to the previous two outbreaks here - in 1877 and 1965 - have been noted by scientists. In each previous case, there was a peak in the number of wild salmon in the particular river system; temperatures had dropped by several degrees in the water; and high water levels in springtime were recorded.
UDN is predominantly a condition of the head skin of salmonid fish native to British and Irish waters, but has occurred in the Baltics and north-west France. It has not been reported in farmed fish to date.
