inted in Great Britain A DIFFERENTIAL VOLUMETRIC MICRO-RESPIROMETER FOR USE WITH SMALL AQUATIC ORGANISMS

A micro-respirometer is described for use with small aquatic organisms whose rates of oxygen consumption fall within the range 0-1-5/il O2 h"1. The major design improvement which this apparatus has over existing models (e.g. Fenn, 1927) is a relatively large capillary bore. Kok, Veltkamp & Gelderman (1953) having shown a proportional decrease in the sensitivity of volumetric respirometers with capillaries smaller than 1 mm diameter. The most recent treatment of the theoretical aspects of differential respirometry is by Umbreit, Burris & Stauffer (1972). The apparatus (Fig. 1 A) comprises a respiration vessel with an alkali well, valve and graduated capillary containing an index drop of Apiezon oil C (Edwards High Vacuum, Crawley), connected by a short length of thin-walled polythene tubing to a compensation system. The respirometer is mounted on a perspex holder and supported by a frame in a water bath. The wide-mouthed respiration and compensation vessels, internal capacities of about 5-5 ml (1 dram vials), were supplied by F. B. G. Trident Ltd., London. The capillary tubing is manufactured by Clay Adams, U.S.A., as 100 /i \ micro-pipette