Relationship between the drift of macroinvertebrates and the activity of brown trout in a small stream

Brown trout Saline trutta were most active in a small stream at night. dusk and dawn when drift rate was highest, but correlations between hourly drif t rates and the trout's activity varied substantially between individuals, between different dates for a single individual, and between different peri ods of the daily cycle. On some occasions. the trout were responsive to the total drift rate, either at night or during the day, and on others to the largest drifting organisms only (terrestrial organisms, adults of Ephemerop tera, Diptera and Trichoptera). The study supports the idea that trout adap t their activity pattern to the abundance of drifting prey, either as gener alists towards any organism, or as specialists towards the largest ones. (C ) 2000 The Fisheries Society of the British Isles.