Effect of time of day on escape response in Pacific staghorn sculpin, Leptocottus armatus

Abstract

The present study aims to test both the daily locomotor activity of Staghorn sculpins (Leptocottus armatus) and the effect of the time of day on the escape response in this species. The daily locomotor activity of 12 individual fish was evaluated in 2 sets coinciding with two opposite tidal stage in nature (low and high tides). Fish displayed mainly nocturnal daily activity (82.5 % of daily activity occurring at night) during a 24 h cycle under a simulated natural photoperiod of 15 h Light: 9 h Darkness (switch on at 05:30 h and switch off at 21:30 h) independently of the tidal phase in nature. Moreover, the escape response to a mechanical stimulus was investigated at 4 different times of day (at 01:30, 07:30, 13:30 and 19:30 h). Sculpin escape response depended on the time of day since lower responsiveness (20.6% of fish showed escape responses) and longer travelled distance (26.40 cm) occurred at night (01:30 h) than during the daytime (58.8% of mean responsiveness and 16.76 cm as mean travelled distance). In contrast, no statistical differences between times of day were found in some escape response parameters, such as directionality (fish always went away), latency, turning angle and turning rate. These results suggested the elusiveness of sculpin is more reduced during their activity phase (at night), but if they then respond to the stimulus, their fast-start performance is greater in terms of travelled distance.