It is important that diel variation in feeding activity is documented before the commencement of studies on the trophic ecology of fishes. If diel patterns in feeding activity are pronounced, then sampling without consideration of such patterns may introduce significant variation into dietary data sets, and even mask spatial and temporal patterns of diet composition that are of primary concern in studies of fish trophic ecology and riverine food webs. Once diel feeding periodicity is understood, it is advisable to concentrate sampling effort on periods of active feeding (Boisclair & Leggett, 1988). Sampling during these peak feeding periods ensures that individual fishes are likely to contain food in their stomachs and avoids the complication that individuals collected at different times of day may be drawn from different feeding populations.