knowledge of lake fish communities of argentine patagonia has grown in the past 20 years thanks to the use of gill nets. however, national park officials and fisher organizations dislike their use and would prefer the use of recreational fisher catch data. the present paper addresses advantages and disadvantages of using gill nets as compared to fishers. this was accomplished by analysis of gill net and fisher catch data from lake guillelmo, parque nacional nahuel huapi for the period 1997-1999. both sets of data revealed the presence of only two salmonids, brook trout (salvelinus fontinalis) and rainbow trout (oncorhynchus mykiss). however, relative abundances of each species differed between fishing techniques, rainbow trout being dominant according to fisher catches and brook trout according to gill net catches. in addition, differences in size, age and spatial distribution brought about by the highly selective nature of fisher catches were clearly observed. this shows that fisher catch data can only be used to assess existing recreational patagonian lake fisheries in terms of current or historical trends in catch composition, structure and fishing pressure. studies of community composition, structure and processes leading to conservation or recreational fishery management should rely on gill net sampling designs tailored to different ecological and management questions, which can be complemented by fisher catch data.