Freshwater Fish Lice Argulus Project

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 2005 they were again 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 these parasites could do significant damage to fish stocks.

As a result of the increased occurrence in 2005 it was considered necessary to establish the extent of the range of Argulus within the Tay system, for only then could any practicable management actions be considered. This survey, which the Tay Foundation supported, was conducted during the summer of 2006. The report is available by clicking here.

Since 2006 reports of Argulus have been relatively few, presumably on account of the fact the summers have generally been wetter.