A novel respirometer for online detection of metabolites in aquaculture research: Evaluation and first applications

In this study we describe a novel flow-through respirometer with automated and semi-continuous detection of key water variables. The recirculating aquaculture system was designed to house aquatic organisms in culture-like conditions and allow long-term, high-precision measurements. Nine respirometry tanks (250 L in volume each) housed animals, and a tenth (without animals) acted as a reference tank. A single measurement unit made sequential measurements of each tank to eliminate the problem of sensor variation associated with multi-probe setups. The accuracy of the analyzers in relation to measurement range was: O2 = 1%; CO2 < 1%; NH3 = 2%; temperature ≤ 0.25%; and pH ± 0.01. Dissolved CO2 was measured using air–water equilibration coupled with non-dispersive infrared detection of carrier gas, and NH3 was quantified using a reagent-based assay and spectophotometric autoanalyzer. Though expensive and not common in aquaculture or physiology research, these two automated metabolite analyzers could operate in both fresh and seawater, and offered high precision and accuracy. We report on the performance of these instruments for aquaculture research in two trials using a freshwater (rainbow trout, Oncorhynchus mykiss) and seawater fish species (turbot, Scophthalmus maximus). One of the main constraints imposed by the sequential measurement of multiple tanks was the measurement frequency of each tank. In the aforementioned system, NH3 analyzes took the longest (12 min), followed by CO2 (7 min), O2 (6 min), and pH (3 min).

► A novel respirometer was constructed to measure metabolite flux for aquaculture studies. ► O2, CO2 and NH3 were analyzed using high precision automated equipment. ► Correcting for washout was important for resolving hourly, but not daily, variation. ► The system was found to perform well in both fresh and saltwater applications.