Respiratory Regulation of the Crayfish (Cambarus immunis).

Some 600 modified Winkler oxygen consumption tests were made to determine (1) the normal variation in oxygen consumption of crayfish under constant oxygen tensions, CO₂ content and H-ion concentration, (2) the effect of H-ion concentration on oxygen consumption, and (3) the oxygen consumption under successively lowered oxygen tensions.

Crayfish were found to exhibit considerable variation in their normal oxygen consumption from hour to hour, the consumption being frequently doubled or halved. Both sexes, in weights ranging from 1.5 to 28.0 gm., exhibit this respiratory fluctuation.

Oxygen consumption determinations for 6 consecutive hours, during which crayfish were tested in water ranging in pH from 6.8 to 5.2, gave no evidence within these limits of a possible effect of H-ion concentration on respiration. The variation in oxygen consumption from hour to hour was of the same magnitude previously determined for normal variation in oxygen consumption under a constant pH.

Respiratory regulation under different oxygen tensions was determined by measuring the oxygen consumption, for successive hours, of crayfish which were steadily lowering the oxygen tension of the water by means of their own respiration. Crayfish were tested individually and in groups of 10. The range of oxygen tensions investigated was from 115% to 8% saturation, partial pressure, at 25° C. Grouping the data according to the weights of the individuals revealed that large animals averaging 17.1 gm. were able to regulate oxygen consumption in a normal manner, down to about 40% saturation Medium-size8 animals, averaging 9.0 gm. regulate down to about 30% saturation, while smaller individuals averaging 4.3 gm. are able to regulate down to about 20% saturation.