Zeitschrift for Z Parasitenkd (1985)71:673-682 Parasitenkunde Parasitology Research 9 Springer-Verlag1985 Studies on the effects of cage culture of fish on the parasite fauna in a lowland freshwater loch in the west of Scotland J.B. McGuigan* and Christina Sommerville Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, UK Abstract. The parasite fauna of cultured and wild fish in an eutrophic lowland freshwater loch in the west of Scotland was studied and com- pared in order to assess the impact of 4 years' fish culture activity on the natural fauna. Strigeid metacercariae dominated the fauna but infec- tion was lower in caged trout than in feral trout and wild fish. Important protozoan pathogens were present and were probably introduced with stocked fish. Intensity of protozoa was low, probably due to therapeutic chemical treatments, with the exception of Trichodina sp. which was a persistent problem. Endoparasitic helminths typical of salmonids were absent. The introduction of a new host species had little effect at this stage on the diversity of the parasitic helminth fauna but probably in- fluenced the relative abundance of certain species. Introduction Recent years have seen increasing interest in the farming of salmonids in floating freshwater cages. From ecological as well as economic viewpoints this recent venture in fish farming is of considerable interest. New types of disease problems are to be expected within such an integrated system. For example, farming activities in a reservoir near Nottingham had to be terminated due to severe infection of trout by the plerocercoid stage of the tapeworm Triaenophorus nodulosus Pallas 1781 (Jarrams et al. 1980). Other cestodes such as Eubothrium crassum Bloch 1779 and Diphylloboth- rium dendriticum Nitzsch 1824 are becoming an increasing problem in sal- monid cage culture operations in various Scottish lochs (Matheson 1979; Wootten and Smith 1979). Relatively little work has been done to investigate the parasites and diseases of cage-cultured fish and the ecological effects of cage culture. Considering the importance of fresh water lochs for water Offprint requests to: C. Sommerville * Present address." Journal of Bone & Joint Surgery, 35/43 Lincoln's Inn Fields, London WC2A 3PN, UK