To investigate the puzzle of whether metabolic rate depression is involved in winter dormancy in fishes, we studied the cunner (Tautogolabrus adspersus), an abundant western North Atlantic wrasse. Like other temperate wrasses [16,29,30], cunner are winter-dormant: they seek refuge within the substrate and become inactive when the ocean cools below approximately 5°C in autumn, and emerge at approximately 5°C the following early summer [31–33]. This winter dormancy in cunner has been associated with a large decrease in metabolic rate that occurs rapidly (within hours) below 5°C and is maintained over the winter [ten,18]. The Q10 of metabolic rate over the transition from active to dormant temperatures has been reported to be greater than 10 in cunner, as in other winter-dormant wrasses , whereas at warmer active temperatures, the Q10 is between 2 and 3, a typical value for fishes [10,34]. Based on this, and consistent with simultaneous reductions in tissue protein synthesis and suppression of appetite and digestion [33,36,37], metabolic rate depression has been implicated as a central component of winter dormancy in cunner. Using cunner as a model, we investigated the hypothesis that the mechanism underlying the energy savings (i.e. low metabolic rate) of winter dormancy in fishes is not metabolic rate depression, but rather a behavioural reduction in activity. We carried out three experiments using automated optical respirometry to allow for multi-day, high-resolution monitoring of whole-animal oxygen consumption rate ( ; a proxy for metabolic rate) even at frigid temperatures. In experiment 1, we examined the influence of acute exposure to low winter temperature on the diel cycle of metabolic rate. In experiment 2, we examined the effect of acute exposure to darkness and low temperature, which are characteristic of the winter refuge, on the diel cycle of metabolic rate and spontaneous activity (measured simultaneously). In experiment 3, we investigated whether chronic acclimation to low temperature can trigger a metabolic rate depression. If metabolic rate depression is involved in winter dormancy, we predicted that the thermal sensitivity (i.e. Q10) of metabolic rate would remain high at all times when cooled below approximately 5°C, including when fish are at rest (i.e. at their SMR at night, as cunner are active during the day ). Alternatively, if reduced activity explains energy savings under winter dormancy, then the thermal sensitivity of metabolic rate during resting periods would indicate physico-chemical effects alone (Q10 ? 2–3) regardless of acute or chronic cold exposure and, in experiment 2, variation in activity would largely explain variation in metabolic rate.
(a) Animals
Adult cunner of combined sexes was basically grabbed having hoop barriers within the summer 2013 for the Conception Bay (47°37?42? N, Amarillo Texas hookup 52°51?31? W), Newfoundland, Canada. The brand new seafood was basically gone to live in holding tanks at the Ocean Sciences Centre (OSC), Memorial College out of Newfoundland, supplied with move-through, temperature-controlled seawater (8–10°C) and confronted by a wintertime photoperiod (eleven L : 13 D). The latest fish was provided so you’re able to satiation regular which have sliced herring.
Teenager cunner out of combined genders have been the 2013 kids of wild-caught mothers away from Placentia Bay (47°42?47? Letter, 53°58?06? W) and Conception Bay, Newfoundland. Spawning, hatching and you can rearing occurred during the OSC on 15°C and several L : a dozen D photoperiod. 3 months ahead of tests, juveniles were relocated to holding tanks, provided with flow-owing to, temperature-regulated seawater (8–10°C) not as much as a wintertime photoperiod (11 L : thirteen D), and you will provided inactive pellets (Gemma; Skretting, St Andrews, NB, Canada).
dos. Situation and methods
An 11 L : thirteen D photoperiod was applied regarding studies because it takes place inside the southeastern Newfoundland, whenever cunner try energetic but getting ready to enter dormancy (October; ocean heat: approx. 9°C and you can air conditioning) or in wintertime dormancy (February; approx. 0°C) [31–33]. Experiments was in fact presented ranging from , for the normal Newfoundland dormancy several months (November–June) .