Effect of closed v. intermittent‐flow respirometry on hypoxia tolerance in the shiner perch Cymatogaster aggregata

Abstract

This study compares the critical oxygen saturation (O 2crit ) levels of the shiner perch Cymatogaster aggregata obtained using two different methods wherein hypoxia is induced either by the fish's respiration (closed respirometry) or by degassing oxygen with nitrogen (intermittent-flow respirometry). Fish exhibited loss of equilibrium at a higher O 2 saturation in the closed respirometry method when compared with the intermittent-flow method. Utilization of closed respirometry yielded O 2crit measurements that were almost twice as high as those obtained with intermittent-flow respirometry. The lower hypoxia tolerance in closed respirometry is consistent with additional stress, caused by a build-up of ammonia and carbon dioxide and a faster rate in dissolved oxygen decline. The results indicate that these two methods of determining hypoxia tolerance in aquatic organisms are not comparable, and that much care should be given to method choice.

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

“…These technique-specific differences in P crit are consistent with a recent study comparing closed and intermittent-flow respirometry (Snyder et al, 2016), which attributed the higher P crit in closed respirometry to metabolic waste accumulation and a faster decline in Pw O2 . Similar factors may be at play in our closed-chamber calorespirometry experiments, resulting in an overestimation P crit .…”

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

“…Though none of these techniques are ideal for all experimental scenarios, intermittent flow respirometry is generally regarded as superior because it avoids the potential accumulation of metabolic end-products presumed to occur in closed respirometry and it has greater temporal resolution than flow-through respirometry (reviewed by Clark et al, 2013;Steffensen, 1989;Svendsen et al, 2016). It has been suggested that the choice of respirometric technique used to determine P crit may influence the results, and indeed P crit in shiner perch (Cymatogaster aggregata) shifted from ∼9.9 kPa to ∼6.1 kPa when using closed-chamber versus intermittent flow respirometry, respectively (Snyder et al, 2016). The authors attribute this to technique, but also discuss the possibility that duration of the P crit trials (∼1 h for closed-chamber, ∼5 h for intermittent flow) may play a role (Snyder et al, 2016).…”

“…It has been suggested that the choice of respirometric technique used to determine P crit may influence the results, and indeed P crit in shiner perch (Cymatogaster aggregata) shifted from ∼9.9 kPa to ∼6.1 kPa when using closed-chamber versus intermittent flow respirometry, respectively (Snyder et al, 2016). The authors attribute this to technique, but also discuss the possibility that duration of the P crit trials (∼1 h for closed-chamber, ∼5 h for intermittent flow) may play a role (Snyder et al, 2016). In the present study, we used modified versions of all three respirometric techniques for our long duration P crit trials, and, despite technique specific-differences and challenges (e.g.…”

“…Keys, 1930;Rogers et al, 2016;Snyder et al, 2016;Steffensen, 1989), but measurements of metabolic end-products in the respirometer chamber are rarely, if ever, reported. To address this knowledge gap, we ran a separate set of closed-circuit P crit trials (91±10 min) to measure accumulated levels of CO 2 and nitrogenous end-products (NH 3 +NH 4 + ).…”

“…We also ran parallel hypoxic exposures of different RHIs to investigate morphological and physiological traits of goldfish that might play causal roles in a time-related shift in P crit , including (among other traits) gill morphometry and Hb-O 2 binding affinity. Furthermore, our use of different respirometric techniques allowed us to disentangle the effects of time and technique on the determination of P crit , thereby addressing a longstanding concern over the use of closed-chamber respirometry and its associated metabolic endproduct accumulation for the determination of P crit (Keys, 1930;Rogers et al, 2016;Snyder et al, 2016;Steffensen, 1989). And finally, we chose goldfish as our study species because they have well-characterized responses to hypoxia exposure (Dhillon et al, 2013;Mitrovic et al, 2009), including a well-resolved P crit as determined by closed-chamber respirometry (Dhillon et al, 2013;Fry and Hart, 1948;Fu et al, 2011;, which could aid our analysis of how RHI might influence the underlying physiology of P crit .…”