DESIGN OF AN ELECTRONICALLY OPERATED FLOW-THROUGH RESPIROMETER AND ITS USE TO INVESTIGATE THE EFFECTS OF COPPER ON THE RESPIRATION RATE OF THE AMPHIPOD GAMMARUS-PULEX (L)

The use of oxygen consumption as a measure of metabolism has resulted in the development of many types of respirometer, These can be classif ied into three types, Firstly, there is the closed system in which oxy gen concentration is measured at the beginning and end of the experime nt and an organism's respiratory rate calculated from the decrease in oxygen concentration and the volume of the vessel (e.g., Franke 1977), Secondly, there is a system in which respired oxygen is replaced by o xygen from the surrounding air and the resultant change in air volume is measured gasometrically (e.g., Pascoe et al. 1968), A third approac h, and the one employed in this study, utilises an open flow-through s ystem in which water passes through a chamber containing an animal and the oxygen concentration is measured and compared to that of a refere nce chamber without an animal, The difference in oxygen concentration is then used to determine the respiration rate of the test animal. In open flow-through systems excretory products are washed away and water is not left stagnant as may occur in closed techniques. In addition, the open flow technique provides a constant oxygen concentration, avoi ds stress to animals with oxygen concentration-dependent metabolism an d allows the simulation of low oxygen tension environments, Despite th ese obvious advantages the use of flow-through respirometers has been somewhat limited due to difficulties in calibration and complexity in construction and operation (Edwards and Learner 1960), The purpose of this investigation was to design a flow-through respirometer which is sufficiently sensitive to detect pollutant-induced respiratory changes in freshwater invertebrates and which permits automated continuous re cording of the respiration of several animals maintained individually, In order to evaluate the system the effect of copper (prepared from c upric sulphate, CuSO4.5H(2)O) on the respiration of the shrimp Gammaru s pulex was studied.