An in situ Evaluation of the Day-to-Day Variation in the Quantity of Food Consumed by Fish

We tested the hypothesis that the mean quantity food consumed by fish in situ does not vary significantly over successive days. The daily ration of minnows (Phoxinus eos × P. neogaeus) was estimated over 5–12 consecutive days (June 1–5, July 6–17, and August 3–9, 1992). Mean daily ration ranged from 0.60 to 1.32 g dry∙100 g wet−1∙d−1 and varied significantly over consecutive days in June and July, but not in August. Average day-to-day variation in food consumption rates ranged from 7.0 to 16.3%. Mean daily ration was not influenced by either water temperature or percent cloudiness. Simulated long-term consumption rates of minnows did not vary by more than 19.3% among sampling intervals ranging from 1 to 30 d. We conclude that long-term consumption rates can be accurately determined using time series of daily ration estimated at 3- to 4-wk intervals.