The present study describes and validates a novel yet simple system for simultaneous in vivo measurements of aquatic CO2 production (MCO2) and oxygen consumption (MO2) rates, thus allowing the calculation of respiratory exchange ratios (RER). Diffusion of CO2 from the aquatic phase into a gas phase, across a hollow fibre membrane, enabled aquatic MCO2 measurements with a high-precision infrared gas CO2 analyser. MO2 was measured with a PO2 optode using a stop-flow approach. Injections of known amounts of CO2 into the apparatus yielded accurate and highly reproducible measurements of CO2 content (R2=0.997, p<0.001). The viability of in vivo measurements was demonstrated on aquatic dragonfly nymphs (Aeshnidae; wet mass 2.17 mg - 1.46 g, n=15) and the apparatus produced precise MCO2 (R2=0.967, p<0.001) and MO2 (R2=0.957, p<0.001); average RER was 0.73±0.06. The described system is scalable, offering great potential for the study of a wide range of aquatic species, including fish.
- Received September 27, 2016.
- Accepted December 30, 2016.
- © 2017. Published by The Company of Biologists Ltd