A simple and affordable calorespirometer for assessing metabolic rates of fishes

Richards

2017

Self Cite

The rate of hypoxia induction (RHI) is an important but overlooked dimension of environmental hypoxia that may affect an organism's survival. We hypothesized that, compared with rapid RHI, gradual RHI will afford an organism more time to alter plastic phenotypes associated with O 2 uptake and subsequently reduce the critical O 2 tension (P crit ) of the rate of O 2 uptake (Ṁ O2 ). We investigated this by determining P crit values for goldfish exposed to short (∼24 min), typical (∼84 min) and long (∼480 min) duration P crit trials to represent different RHIs. Consistent with our predictions, long duration P crit trials yielded significantly lower P crit values (1.0-1.4 kPa) than short and typical duration trials, which did not differ (2.6±0.3 and 2.5 ±0.2 kPa, respectively). Parallel experiments revealed these timerelated shifts in P crit were associated with changes to aspects of the O 2 transport cascade that took place over the hypoxia exposures: gill surface areas and haemoglobin-O 2 binding affinities were significantly higher in fish exposed to gradual RHIs over 480 min than fish exposed to rapid RHIs over 60 min. Our results also revealed that the choice of respirometric technique (i.e. closed versus intermittent) does not affect P crit or routine Ṁ O2 , despite the significantly reduced water pH and elevated CO 2 and ammonia levels measured following closed-circuit P crit trials of ∼90 min. Together, our results demonstrate that gradual RHIs result in alterations to physiological parameters that enhance O 2 uptake in hypoxic environments. An organism's innate P crit is therefore most accurately determined using rapid RHIs (<90 min) so as to avoid the confounding effects of hypoxic acclimation.

Section: Respirometrymentioning

confidence: 99%

Rates of hypoxia induction alter mechanisms of O2 uptake and the critical O2 tension of goldfish

Richards

2017

Self Cite

Section: Calorespirometermentioning

confidence: 99%

“…The design and operation of the calorespirometer are described in detail in Regan et al (2013). Briefly, the metabolic heat of a fish is detected as a voltage by a collection of Peltier units (Custom Thermoelectric Peltier module 12711-5L31-03CQ, Bishopville, MD, USA) via the Seebeck effect and converted to wattage using an empirically determined calibration coefficient (see Regan et al, 2013). The design of the calorespirometer allows for the simultaneous measurements of metabolic heat and ṀO 2 using P O2 optodes (Ocean Optics OR125, Dunedin, FL, USA) placed on the inflowing and outflowing water lines as well as in the fish chamber.…”

Section: Calorespirometermentioning

confidence: 99%

“…We used calorespirometry because it is the 'gold standard' of MR measurements and the only way to accurately measure MR on hypoxemic animals in real time (see Kaiyala and Ramsay, 2011;Nelson, 2016). Despite the superiority of calorespirometry, only a few studies have measured the metabolic heat of fishes (Addink et al, 1991;Regan et al, 2013;Stangl and Wegener, 1996;van Ginneken et al, 1994van Ginneken et al, , 1997van Ginneken et al, , 2004van Waversveld et al, 1989), and only three of these (van Ginneken et al, 1994(van Ginneken et al, , 1997(van Ginneken et al, , 2004 have measured metabolic heat at Pw O2 other than normoxia and anoxia. While the data from these studies suggest that MRD is employed at hypoxic Pw O2 values, they exposed their organisms to progressive hypoxia over sometimes prolonged periods of time and they did not relate their measurements to P crit nor directly assess the contributions of anaerobic metabolism at various hypoxic Pw O2 values.…”

Section: Introductionmentioning

confidence: 99%

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Calorespirometry reveals that goldfish prioritize aerobic metabolism over metabolic rate depression in all but near-anoxic environments

Gill

Richards

2016

Self Cite

Metabolic rate depression (MRD) has long been proposed as the key metabolic strategy of hypoxic survival, but surprisingly, the effects of changes in hypoxic O 2 tensions (Pw O2 ) on MRD are largely unexplored. We simultaneously measured the O 2 consumption rate (Ṁ O2 ) and metabolic heat of goldfish using calorespirometry to test the hypothesis that MRD is employed at hypoxic Pw O2 values and initiated just below P crit , the Pw O2 below which Ṁ O2 is forced to progressively decline as the fish oxyconforms to decreasing Pw O2 . Specifically, we used closed-chamber and flow-through calorespirometry together with terminal sampling experiments to examine the effects of Pw O2 and time on Ṁ O2 , metabolic heat and anaerobic metabolism (lactate and ethanol production). The closedchamber and flow-through experiments yielded slightly different results. Under closed-chamber conditions with a continually decreasing Pw O2 , goldfish showed a P crit of 3.0±0.3 kPa and metabolic heat production was only depressed at Pw O2 between 0 and 0.67 kPa. Under flow-through conditions with Pw O2 held at a variety of oxygen tensions for 1 and 4 h, goldfish also initiated MRD between 0 and 0.67 kPa but maintained Ṁ O2 to 0.67 kPa, indicating that P crit is at or below this Pw O2 . Anaerobic metabolism was strongly activated at Pw O2 ≤1.3 kPa, but only used within the first hour at 1.3 and 0.67 kPa, as anaerobic end-products did not accumulate between 1 and 4 h exposure. Taken together, it appears that goldfish reserve MRD for near-anoxia, supporting routine metabolic rate at sub-P crit Pw O2 values with the help of anaerobic glycolysis in the closed-chamber experiments, and aerobically after an initial (<1 h) activation of anaerobic metabolism in the flow-through experiments, even at 0.67 kPa Pw O2 .

“…Heat calibration, completed using the procedure described by Regan et al (2013), showed that 1 mV was equal to 0.67 mW. The calibration also revealed that the calorimeter achieved thermal equilibrium after approximately 2 h. This time lag was factored out of the heat traces using an 'instantaneous correction' (Bartholomew et al, 1981) for flow-through respirometry corrected for calorimetric heat data.…”

Section: Calorimetermentioning

confidence: 99%

Characterizing the metabolic capacity of the anoxic hagfish heart

Gillis

Cox

et al. 2015

Pacific hagfish, Eptatretus stoutii, can recover from 36 h of anoxia at 10°C. Such anoxia tolerance demands the mobilization of anaerobic fuels and the removal of metabolic wastes -processes that require a functional heart. The purpose of this study was to measure the metabolic response of the excised, cannulated hagfish heart to anoxia using direct calorimetry. These experiments were coupled with measurements of cardiac pH and metabolite concentrations, at multiple time points, to monitor acid-base balance and anaerobic ATP production. We also exposed hagfish to anoxia to compare the in vitro responses of the excised hearts with the in vivo responses. The calorimetry results revealed a significant reduction in the rate of metabolic heat production over the first hour of anoxia exposure, and a recovery over the subsequent 6 h. This response is likely attributable to a rapid anoxia-induced depression of aerobic ATP-production pathways followed by an upregulation of anaerobic ATP-production pathways such that the ATP production rate was restored to that measured in normoxia. Glycogen-depletion measurements suggest that metabolic processes were initially supported by glycolysis but that an alternative fuel source was used to support the sustained rates of ATP production. The maintenance of intracellular pH during anoxia indicates a remarkable ability of the myocytes to buffer/regulate protons and thus protect cardiac function. Altogether, these results illustrate that the low metabolic demand of the hagfish heart allows for near-routine levels of cardiac metabolism to be supported anaerobically. This is probably a significant contributor to the hagfish's exceptional anoxia tolerance.