Short Communication a Method for Long-term Multiple-channel Recording of Oxygen Consumption in Aquatic Animals

The objective of the present work has been to develop a method for measuring the rate of oxygen consumption on a routine basis during toxicity testing and environmental monitoring. This requires a method that is reliable over long periods and can be used with a minimum of maintenance work in a variable environment. The system should consist of a compact unit easily transported and available at a reasonable cost. Visual updated records of the oxygen consumption should be available at all times. A compact unit for continuous long-term multiple-channel recording of oxygen consumption in an open flow-through system has been developed. The system has primarily been designed for use in routine ecotoxicological testing and monitoring during suboptimal recording conditions. The unit is built around a single standard oxygen electrode inside a multiple-port system with 12 input channels, which successively collect water from the respiration chambers. By using frequent calibrations, the effects of chemicals on the electrode and variations in recording conditions, such as temperature changes, are compensated for. Emphasis has been placed on the use of simple mechanical components and a modular principle that allows a large degree of freedom for modifications through exchange of components. The system was tested with blue mussels (Mytilus edulis), during exposure to a number of organic and inorganic chemicals. Computer control of the system is based on a minimum of peripheral lines (two analogue inputs and two digital lines). The software is entirely screen-based and has few input variables with a number of continuously updated graphical and numerical displays that convey information about the status of the experiment. The driving force for flow through the system is the pressure difference between the inlet and the outlet created by the difference between the surface levels of the two water columns (Fig. 1). The flow into each chamber is regulated by reduction valves made from Teflon capillary tubes. The flow rate through the tube is described by the Poiseuille–Hagen equation: