I. Macroinvertebrate abundance and production were compared between an open and shaded site of a stream in the Wasatch Mountains, Utah. Mean biomass was significantly higher at the open site for midges (Chironomidae), 4.6x; Baetis hicaudatus, 5.7x; Baetis tricaudatus, 2.3x; Drunella coloradensis, 12x and Cinygmula sp., L6x.Abundance of most other macroinvertebrates (except black flies; Simuliidae) was also greater at the open site, but differences were not significant. Black fly biomass was 1.7x greater at the shaded site.2. Seasonal production, estimated by the size-frequency and instantaneous growth rate methods, was greater at the open site than the shaded site for most taxa (except black flies) and reflected differences in standing crops between the sites rather than differences in rate of growth. Excluding black flies, production at the open site was twice as high as at the shaded site.3. The greater abundance and production of most invertebrate taxa at the open site is probably associated with either higher quality food (algae and algal detritus), or a phototactic attraction to sunlit areas.4. Sampling of large cobbles was an efficient method of sampling all taxa except Cinygmula sp. which was more abundant on smaller substrate particles.

Larval lake whitefish Coregonus clupeaformis 14–18 mm long preferred copepods, especially Diaptomus sicilis, to cladocerans and rotifers. All sizes of zooplankton were eaten but few larger zooplankters (>2.0 mm) were selected. Size, pigmentation, and movements of the zooplankters probably influence the apparent preferences of the fish as measured by the linear food selection index.

Rainbow trout Oncorhynchus mykiss cultured under hatchery conditions were exposed to hyperoxia by injection of oxygen into the rearing water. In two separate studies of 67 and 73 d, mean hemoglobin of experimental fish reared at oxygen levels averaging 147-220% saturation was 7.8-8.7% lower than that of control fish reared at mean oxygen saturations of 66-74%. Mean hematocrit of experimental fish was also 3.1-5.7% lower than that of control fish. Fish reared in hyperoxic conditions did not differ in growth, survival, or behavior from control fish. Fish exposed to hyperoxia rapidly adjusted hemoglobin and hematocrit to levels similar to those of control fish after oxygen injection was stopped.

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