Freshwater Fish Louse Argulus

Freshwater lice, Argulus, are parasites which live on the skin of a fish, and like the much better known sea lice, they eat the skin of fish. In appearance they have similarities to sea lice, except the bodies of the adults are slightly larger, clearish in colour with prominent eyes. They thrive in warm weather and especially in slow or still water and in prolific outbreaks can cause significant damage to fish.

It is not known how this parasite reached Tayside but they appear to have been present in the lower reaches of the Earn for at least several decades and in the 1990s caused serious problems in a rainbow trout fishery near Bridge of Earn and in Glenfarg Reservoir which is supplied with water pumped from the Earn. Some were also found at that time in the lower Tay. In the last two years they have again been seen on juvenile salmon and brown trout in the lower Tay and there are reports from lochs in the Blairgowrie area. In dry warm summers like 2005, these parasites could do significant damage to fish stocks.

In the first instance it is necessary to establish exactly the extent of their range within the Tay system and only then can any practicable management actions be considered. The Tay Foundation is supporting a survey of fish during the summer of 2006 to establish this.