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Oxygen Consumption of Crayfish under Different Temperature Regimes
Monitoring with oxygen microsensors and the OXY-4 micro
Tanja Soukup, Joachim Henjes, and Matthew James Slater
Alfred Wegener Institute, Helmholtz Centre for Polar- and Marine Research (AWI), Bremerhaven, Germany
The narrow clawed crayfish is able to withstand increased temperatures (≥ 26 °C) for medium term periods, but it is still unknown what happens to the organism during the exposure to this kind of stress. One part of the investigation is to measure oxygen consumption at different temperatures, which is expected to increase with rising temperatures. Oxygen microsensors and the oxygen meter OXY-4 micro together with four chambers and a flow-through respirometry system have been used to measure the oxygen consumption of three animals at different temperatures during the same experimental period.
Materials & Methods
For the experimental set-up a flow-through respirometry system has been chosen, because it enables long term measurements without oxygen- or handling stress for the crayfish. Each chamber was connected with a tube to a peristaltic pump so that the water flow could be adjusted separately to the needs of each crayfish (Fig. 1, left). The four oxygen microsensors with screw thread (type Heilmeyer) could easily be connected to the current system in the tubes by a T-piece adapter, which also protected the microsensors during handling the tubes. The connection was sealed with a piece of tube and Parafilm® to prevent air leaks. Calibration of the oxygen microsensors had to be conducted every day before measurement using aerated water (100% air saturated) and a saturated sodium metabisulphite solution (0% air saturated) to ensure the correct baselines. The communication between the oxygen microsensors, the OXY-4 micro and the software was easily established using the supplied serial cables and no problems occurred using the serial to USB adapter. Due to the compact sizes of the transmitter and the microsensors the experimental set-up did not require much space.
Using the OXY-4 micro transmitter enabled measuring oxygen concentration of the outflowing water of four different chambers with different temperatures. Thus, one measurement consisted of three chambers with one crayfish each and one empty chamber as a bacterial oxygen consumption control. Due to the live view concept of the software it was easy to adjust the oxygen concentration in the chambers at the beginning of each trial and to monitor the recording (Fig. 2, right).
Results & Discussion
The live view monitoring already showed robust and applicable data. The microsensors reacted fast to changing oxygen concentrations in the current inside the tubes caused by changing oxygen concentration in the chambers. Small reactions of the crayfish to stressors like beginning molting event were easy to determine (Fig. 1, green arrow). Overall, the oxygen microsensors stayed in water over three month and were active over 100 hrs, but still working very well showing good phase and amplitude values.
Some problems occurred with the ongoing experiment especially in the systems with rising temperatures because of growing biofilm within the tubes. Frequently detached particles sticking temporarily to the used microsensors caused peaks in the oxygen readings and falsified the oxygen consumption results (Fig. 3, red arrow). Hence it was important to keep biofilm production to a minimum even so the oxygen consumption of the biofilm could be subtracted from the result using the empty chambers.
Needle-type oxygen microsensors enabled long term oxygen consumption analysis in a flow-through respirometry system. Even small stress events for the tested crayfish could be detected in the onlie measurements. During the whole experiment no problems occurred with the communication between oxygen microsensors, oxygen meter, computer software and data logging, respectively. The sensors worked reliably over the whole long term measurement period. The created “txt”-files are easy to handle and to import in Excel or other data working programs. Simultanous online monitoring with four microsensors and the live display of all measurements is a great advantage and especially eased the adjustment of starting conditions in our experiment.