Is the diel cycle of metabolic rate in mummichog (Fundulus heteroclitus) affected by near infrared lighting used for daytime and nighttime video recordings of behaviour?
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Date
2023-04
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University of New Brunswick
Abstract
Spontaneous activity, which is the routine volitional movements of an animal, is a fundamental behavioural trait that commonly shows a strong diel cycle in animals. Mummichog (Fundulus heteroclitus) are an important estuarine fish, with a historically documented diurnal diel cycle (i.e., being more active during the daylight hours). Recent laboratory studies, however, have reported that mummichog have a free-running (i.e., similarly active regardless of time of day) or nocturnal diel cycle of activity (i.e., more active at nighttime). In the laboratory, activity is often recorded using near-infrared (NIR) lights to illuminate the fish so that a NIR sensitive camera can visualize and record activity across the normal light-dark periods of the 24-hour day. A proxy for activity, when we cannot measure it directly, is whole-animal metabolic rate (MO2) because movement is correlated with oxygen consumption rate. Since NIR light is close to the visible light spectrum, and certain fish show some sensitivity to NIR, its use could explain the uncertainty about the diel cycle of activity in mummichogs. To determine if NIR lighting can influence diel cycles of activity, I measured MO2 of mummichogs over four-day (Experiment 1) or six-day (Experiment 2) periods with alternating on-off regimes of NIR lighting: NIR off-on (two days each) for Experiment 1, or NIR off-on-off (two days each) or the reverse (on-off-on) for Experiment 2. NIR lights did not influence the diel cycle of MO2, which strongly suggests that mummichog do indeed have a nocturnal, but relatively free-running, diel cycle of activity. NIR illumination is a suitable method to visualize mummichog during light-dark diel cycles.