Repeated measurement ofMo₂in small aquatic organisms: a manual intermittent flow respirometer using off-the-shelf components

Abstract

Measurement of rates of oxygen consumption ( Mo) in small aquatic embryos or larvae (<1 mm) in response to altered environmental conditions has traditionally been challenging. Here, using modifications of a commercially available fluorescent optode flow-through cell (FTC; PreSens FTC-PSt3) and routine laboratory supplies (syringes, stopcocks, tubing), we have constructed a manual intermittent flow respirometer (MIFR) that allows measurement of Mo in small numbers of individuals when sequentially exposed to different environmental conditions (e.g., changes in seawater pH) through a gravity-driven media replacement perfusion system. We first show that the FTC can be used in "static" mode while incubating small numbers of embryos/larvae contained within the planar oxygen sensor (POS) chamber with Nitex filters. We then demonstrate the use of the MIFR by exposing larval echinoderms ( Fellaster zelandiae, Evechinus chloroticus, and Centrostephanus rodgersii) to seawater equilibrated with elevated CO and measured Mo during acute and chronic exposure to hypercapnia. This MIFR method will allow investigators to address questions regarding the respiratory physiology of small aquatic animals, such as the thresholds for metabolic depression in embryonic and larval forms. NEW & NOTEWORTHY A manual intermittent flow respirometer (MIFR), allowing media exchange in a flow-through cell containing small aquatic organisms, permits repeated measurement of Mo of individuals not only in a single medium (e.g., technical replication), but also in different media (here, high CO-equilibrated seawater), enabling measurement of acute physiological responses to changed conditions. This versatile technique has wide-ranging implications for the study of the Mo response of aquatic organisms in the face of climate change.

Glucose uptake as an alternative to oxygen uptake for assessing metabolic rate in Danio rerio larvae

“…We did not include a mixing recirculation loop in the current study. This was omitted in favour of reducing the total volume of the respirometer, improving detection of small changes in oxygen saturation and limiting bacterial respiration, as reported for other low volume respirometry studies ( Folkerts et al, 2017 ; Baker et al, 2018b ; Rodgers et al, 2016 ). The recirculation pump in the ambient water bath in which the chambers were placed ensured consistent water temperature and caused turbulence (i.e., agitation of the chambers) similar to the gentle shaking used by ( Parker et al, 2020 ).…”

“…Regression curves were generated using AquaResp from the 300 data points collected during each trial. An R2 cut off of ≥0.85 was used ( Baker et al, 2018 ). The slope of the regression curves represents the change in oxygen saturation (ΔO 2 ) of the water within each chamber.…”

“…While 96 well plate systems exist for increasing throughput when measuring whole organismal metabolism of small animals, these systems are also costly. Indeed, due to the cost of professionally manufactured respirometry systems, there are publications designed to help interested parties build their own from off-the-shelf components ( Baker et al, 2018a ).…”

Integrative biology of injury in animals

“…By contrast, more recent studies predominantly use respirometry (e.g. Baker et al ., 2018 ; Ferreira et al ., 2020 ; Tomlinson et al ., 2018 ). Measurements of whole‐body metabolism also give little indication of changes at smaller spatial scales, such as those limited to the wound‐adjacent area, limiting our understanding of what specific processes (e.g.…”