In Finland, most of inland water areas are either private or state-owned. Most private waters are owned by a shareholders' association for areas held in common by a registered village, represented by a fishing co-operative. This kind of joint possession of private waters is a feature in Finnish legislation that distinguishes fisheries management from elsewhere in Europe, except Sweden. State-owned waters are managed by fisheries region management units as regards public waters, or their management is handed over to a state-owned enterprise. Due to mosaic ownership many fishermen utilise simultaneously private and state-owned waters, termed here combined waters. The aim of this study, which involved 53 out of a total of 225 fishermen active in 1990, was to examine how the type of water ownership affected professional fishing practices. The data were collected through personal interviews. On the basis of the fishermen's behaviour in response to diminishing fish stocks they have been classified into four groups. Efforts were made to determine whether the pattern of ownership influenced the process of adaptation. Vendace ( Coregonus albula L.) is the most important commercial species in Finnish inland waters. State-ownership facilitates the starting up of professional fishing enterprises, providing for equality in obtaining fishing licences, use of the most effective fishing technology, trawling, and highest turnover. The joint possession of private waters in fishing co-operatives results in conservative decision-making and encourages the use of less efficient gear, winter seine. In waters of fishing co-operatives, fishing rights are allocated between shareholders not as dependent on fishery income as fishermen using state-owned waters. The average annual catch per enterprise in winter seining was half of that of trawling. Restrictive policy in fishing co-operative waters results in biological under-utilization of vendace resources, because effective fishing is considered as being the best way of managing vendace stocks. The most prominent distinctive feature of these types of ownership was the attitude to entrepreneurship, which was hampered in privately owned waters. All fishermen expressing a passive form of `adaptation' to diminishing fish stocks fished in waters belonging entirely or partly to fishing co-operatives.