The notion that less interest explains lower metabolic rates inside winter season-inactive fishes originated early work because of the Crawshaw and you will co-specialists [nine,19,20]

_ten ? 2–3) in largemouth bass and brown bullhead catfish when cooled to winter temperatures, concluding that metabolic rate depression is not involved in these species during winter dormancy. Crawshaw and co-workers recognized that cold-induced decreases in activity were characteristic of winter dormancy, but they were cautious about specifying its contribution to reductions of metabolic rate . In part, this reflected the greater logistical challenges at that time of making simultaneous measurements of metabolic rate and activity, as well as the fact that they seem to have serendipitously measured metabolic rate under relatively inactive periods so never saw substantial variation in metabolic rate. Additionally, they calculated Q₁₀ values over wider temperature ranges, which can obscure more sensitive periods that may occur when the fish transitions across the active–dormant threshold temperature. In any case, their results have been widely interpreted as being species-specific responses that contrasted with the numerous other winter-dormant fishes where metabolic rate depression has been implied on the basis of relatively high thermal sensitivity of metabolic rate at low temperatures [10,13–18]. However, the thermal sensitivity of SMR in cunner is no different from that in the largemouth bass or catfish studied by Crawshaw and co-workers [9,19 https://datingranking.net/it/valuta-il-mio-appuntamento/,20] and, combined, our studies suggest the absence of metabolic rate depression in winter-dormant fishes.

(b) This new influence out-of darkness with the hobby and k-calorie burning away from winter season-inactive fishes

The persistent inactivity in winter-dormant cunner is induced by low temperatures, but an additional key environmental influence to consider is the darkness that is characteristic of the winter refuge buried within the substrate. Wrasses, including cunner, are diurnal fishes with distinct day–night cycles of activity and sleep-like behaviour at night . Typical of day-active fishes [49,50], cunner under warm conditions showed a diel rhythm of elevated metabolic rate during the active daytime and stable low metabolic rate during night-time rest (figures 1a and 2a). Low temperature greatly dampens these diel cycles (figure 1a) such that day- and night-time metabolic rates are similar under winter-dormant conditions (figure 1b,c). To our knowledge, this is the first demonstration that low temperature can abolish diel cycles in activity and metabolic rate in fish. Perpetual darkness (0 L : 24 D) at warm temperature has the same effect, similar to other wrasse species , though more variability in rates is visually apparent (figure 2a,b). The combination of cold and dark resulted in a particularly marked flatline in activity and metabolic rate (figure 2a). Although darkness has been implicated as a metabolic signal in hibernating mammals and possibly reptiles , darkness is not a trigger for metabolic rate depression in winter-dormant cunner; metabolic rate in the cold and dark did not show elevated Q₁₀ when compared with warm inactive periods (figure 2b and table 1). Interestingly, even after 2 days of cold and darkness, cunner remain vigilant of light as they responded to reappearance of light by becoming temporarily active and thus increasing metabolic rate (figure 2a). Thus, although low temperature alone can trigger the behavioural and metabolic phenotype of winter-dormant cunner, the darkness of the refuge may be an additional cue that further minimizes fluctuations in activity and thus metabolic rate during winter dormancy. Vigilance to light occurs even in profoundly metabolically depressed hibernating turtles , and may be a general attribute of winter-dormant animals to detect changes in seasonal photoperiod in preparation for exit from dormancy. The influence of darkness may be particularly important for winter-dormant fishes in polar regions , where the seasonal change in photoperiod is massive while temperature changes marginally.