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ment as to what length of stream constitutes a most appropriate and cost-effective collecting activity. In many standardized procedures, a reach of 100 m has been adopted for small- to medium-sized streams. In contrast, my collections at a site have always in- cluded a minimum of 200 m-often up to 400 m-of stream, in order to sample sufficient distance to find representative habitat for all species that are pres- ent. In 1988, I compared fish collections in adjacent 100-m sections of Brier Creek at a total of 5 sites, or 10 segments. Typically, the overall fish assem- blage in spatially adjacent 100-m segments had per- cent similarity in composition of only 60-70%, and hence a different picture of the fish community re- sulted if a total of 200 m was included in the sample instead of only 100 m. Accordingly, in at least some midwestern streams, I suggest that more than 100 m of stream reach should bl'l sampled, whether the goal of the study is assessment of some par- ticular effect or the acquisition of long-term data on basic ecological properties of the fish community. ~ FISH COMMUNITY STRUCTURE 17 Information Sources Gelwick, F. P. 1990. Longitudinal and temporal com- parisons of riffle and pool fish assemblages in an Ozark stream. Copeia 1990. In press. Harvey, B. C. 1987. Susceptibility of young-of-the-year fishes to downstream displacement by flooding. Trans. Am. Fish. Soc. 116:851-855. Matthews, W. J. 1986. Fish faunal structure in an Ozark stream: stability, persistence, and a catastrophic flood. Copeia 1986:388-397. Matthews, W. J. 1987. Physicochemical tolerance and selectivity of stream fishes as related to their geographic ranges and local distributions. Pages 111-120 in W. J. Matthews and D. C. Heins, eds. Com- munity and evolutionary ecology of North American stream fishes. University of Oklahoma Press, Norman. 310 pp. Matthews, W. J., R. C. Cashner, and F. P. Gelwick. 1988. Stability and persistence of fish faunas and assemblages in three midwestern streams. Copeia 1988:947-957. Ross, S. T., W. J. Matthews, and A. A. Echelle. 1985. Per- sistence of stream fish assemblages: effects of environ- mental change. Am. Nat. 126:24-40.