SynopsisThe effect of siltation on stream fish in northeast Missouri was evaluated using community structural measurements and a functional approach that emphasized feeding and reproductive guilds. As the percentage of fine substrate increased, the distinction among riffle, run, and pool communities decreased, primarily because the number of individuals of typical riffle species decreased. Within the riffle communities the abundance of fish of two feeding guilds -benthic insectivores and herbivores -was reduced as the percent of fine substrate increased. The abundance of fish in other feeding guilds was not affected. The only reproductive guild to be similarly affected was the simple and lithophilous, whose members require a clean gravel substrate for spawning. Species within each guild affected by siltation had significantly similar trends in abundance. The guild analysis indicated that species with similar ecological requirements had a common response to habitat degradation by siltation.

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We monitored the movement and habitat use of 34 stream‐dwelling smallmouth bass Micropterus dolomieui in Jacks Fork River, Missouri, by radiotelemetry. Observations were made 24 h/d in all seasons. Definite patterns of diel activity and habitat use were evident and were modified by seasonal changes in water temperature. Fish remained in restricted home ranges for most of the year but tended to disperse in spring when all of the radio‐tagged fish left their home pool; 75% returned during the same season. Equal numbers of fish moved upstream and downstream. However, the median distance moved upstream was greater. Intrapool movement of smallmouth bass peaked soon after sunrise and again after sunset in all seasons. Average intrapool movement was 120 m/d when water temperatures were lowest (4°C) and 980 m/d when temperatures were highest (27.5°C). In the warmer seasons, fish preferred logjams and root wads by day and increased their use of boulders at night. In cooler seasons, fish used boulders almost exclusively. Regardless of season, open water without cover was used most during the period just after sunrise but was never used in proportion to its availability. Boulders were the most preferred substrate, and gravel was the least preferred. Small mouth bass used intermediate depths the most and showed no daily or seasonal changes in depth preferences. Fish preferred velocities less than 0.2 m/s at all times of day and in all seasons. Movements in floods did not differ from those observed during normal discharges; however, single logs were selected in significantly greater proportion than logjams.