Abstract
Meaningful estimates of fish species richness in streams for assessments of environmental quality or community-level ecological analyses can be achieved only if the length of each stream segment sampled approaches or exceeds the length at which the cumulative species number becomes asymptotic. I used data from 10 representative sites on nine southern Wisconsin warm-water streams to determine the length of stream that should be sampled when species richness is estimated with a type of towed electrofishing unit commonly used in the midwestern USA. The estimated length of stream necessary to reach an asymptotic species number varied among sites; it was not related to estimated species richness, and it was only weakly and nonsignificantly correlated (positively) with stream size, Although much shorter distances were sufficient at some sites, a stream length of 35 times the mean stream width (at normal base flow), or a length equal to three complete riffle-pool sequences, ensured that the cumulative n...

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