CONCENTRATIONS OF WILD AND ESCAPED FISHES IMMEDIATELY ADJACENT TO FISH FARM CAGES

Beach-seine netting was carried out adjacent to five cage farms (two freshwater, three marine) and at respective control sites, in Argyll, western Scotland. Cages held captive rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri) and/or Atlantic salmon (Salmo salar) which were fed pelleted feed. In each case, the total number and weight of fishes caught beside farm cages were greater than at their respective control sites. The most common species adjacent to freshwater farms was rainbow trout. These fish were thought to have escaped from cages and many had eaten pelleted food. This was the only group to have done so. In contrast, the fish caught at marine farms were wild fishes, particularly saithe (Pollachius virens). This was the only species found to have eaten pelleted food and individuals containing pellets were caught at both farm and control sites. Reasons for the apparent large concentrations of fishes close to cages and the possible consequences for the aquaculture industry are discussed. © 1990.