A novel technique for the precise measurement of CO2 production rate in small aquatic organisms as validated on aeshnid dragonfly nymphs.

The present study describes and validates a novel yet simple system for simultaneous in vivo measurements of rates of aquatic CO2 production (ṀCO2) and oxygen consumption (Ṁ O2), 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 ;ṀCO2 measurements with a high-precision infrared gas CO2 analyser. ṀO2 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 ṀCO2 (R²=0.967, P<0.001) and ;ṀO2 (R²=0.957, P<0.001) measurements; 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. [ABSTRACT FROM AUTHOR]