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temperatures averaged 13.20C (range 11-160C). Daily backwater temperature fluctuation was not as great (i60C) as in April (i90C), and catches were lower (Table 1). Squawfish abundance was not significantly correlated with water temperature (r= 0.64, p= 0.17). Thirty-five young fish were captured and recaptured in more than one habitat, and 17 fish marked in habitats on one side of the river (Figure 2) were subsequently recaptured on the other side (Table 1, Figure 2). Only thirty-one young Colorado squawfish were captured in November, 1981. Of these, 21 were new captures (n= 21, x= 43, SO= 8) and 10 were recaptures that were marked in October. Most of these (96.8%) were captured in the backwater, including all of the marked fish (Table 1). Backwater and main channel temperatures averaged only 8.60C (range= 7- I20C) and 7.30C (range= 6.S-8.S0C), respectively. Fish abundance was not correlated with backwater temperatures (r=0.04, p= 0.94). Ten fish species were sympatric with young Colorado squawfish. Of 5,30S fish captured in backwaters used by young squawfish in 1981, the most abundant were red shiner ~otropis lutrensis (8S.6%), Colorado squawfish (7.8%), fathead minnow Pimephales promelas (S.2%), and flannelmouth sucker Catostomus latipinnis (1.1%). Captures of red shiner and fathead minnow varied between sample periods but were not correlated with water temperatures in April, October, or November (red shiner, r<0.17, p>0.38; fathead minnow, r<0.34, p>O.SO). Discussion I found that young Colorado squawfish used backwaters but also moved into other shoreline habitats. Some marked fish were recaptured in locations that were directly across the river channel. This demonstrated their ability to negotiate river currents, ostensibly to seek more suitable habitats. Other workers have also reported that young Colorado squawfish occupy shoreline backwater habitats (Taba et al. 1965, Holden and Stalnaker 1975, Seethaler 1978), but their movements between backwaters and nearby habitats have been little studied. Holden (1977) marked 87 age-O Colorado squawfish in a backwater, but recaptured only about 3% of the marked fish during a two-day period at that location. He speculated that the fish were still present in the backwaters but were hard to catch (Holden 1977). My study indicated that the fish moved among different habitats during a 24-h period but may remain in the same general area for up to a month. Most Colorado squawfish were captured in backwaters in April, when water temperatures equalled or exceeded mainstream temperatures (i.e. from late morning to evening). Fewer fish were captured in backwaters when mainstream temperatures were higher (i.e. early to mid-morning) or in autumn when water temperatures were low. Thus, diel backwater abundance was positively related to backwater temperatures and negatively related to river temperatures. This relationship was highest when the backwater/main-channel temperature differential was high and lower when the differential was low. Other environmental factors also vary within a 24-h period, and identification of specific factors providing "zeitgebers" (signals) for biorhythms in these riverine fish may be difficult to determine. In general, the most important factor influencing diel activity of fishes has been attributed to the alteration between light and dark period that occurs at dawn and dusk (Muller 1978). Young squawfish did not move into, or leave backwaters directly in response to dawn or dusk (e.g., high/low numbers at dawn or shortly thereafter or low/high numbers at dusk), thus the light/dark alteration did not appear a major influence on diel activity. However, interacting factors (e.g., phototaxis or a response to other parameters) may have also affected diel movements, and 48