Diel activity patterns of the fish community in a temperate stream.

The diel activity patterns of fishes in a temperate New Brunswick stream were studied during the summer over 5 years. Young-of-the year Atlantic salmon Salmo salar and blacknose dace Rhinichthys atratulus were more active during the day than at night, whereas lake chub Couesius plumbeus, brook trout Salvelinus fontinalis and adult white suckers Catostomus commersonii were more active at night than during the day. Because fishes were as likely to be nocturnal as diurnal, the data suggest that more night-time sampling is needed to provide an unbiased view of fish community structure in temperate streams.

Combined effects of chemical and visual information in eliciting antipredator behaviour in juvenile Atlantic salmon Salmo salar.

Under natural conditions, both young-of-the-year (YOY; 0+ year) and parr (1+ year) Atlantic salmon Salmo salar exhibited strong antipredator behaviour (e.g. increase in latency to resume foraging) following the exposure to damage-released chemical alarm cues relative to a stream water control. Subsequent exposure to a novel visual stimulus had contrasting results. Parr increased their reactive distance to the visual stimulus if they had been previously exposed to a chemical alarm cue, whereas YOY did not. On the other hand, both YOY and parr took significantly longer to resume foraging when exposed to a visual stimulus if they had been previously exposed to a chemical alarm cue than control groups. While YOY and parr differed in the type and intensity of antipredator responses to both chemical and visual stimuli, perhaps due to differential costs and benefits associated with age, both used the chemical and the visual information in a combined manner.