Respiratory energy losses in the protozoan predator Didinium nasutum Müller (Ciliophora).

Respiration in Didinium nasutum, an active protozoan predator, was investigated in relation to cell weight at 10, 15, and 20° C by means of cartesian diver microrespirometry. Oxygen uptake increased progressively over the 10-20° C temperature range; a table of Q related to weight is presented. Regression coefficients of log weight versus log oxygen uptake (b) were 0.96 at 10° C, 0.98 at 15° C and 1.00 at 20° C. D. nasutum was shown to expend very much higher levels of respiratory energy than a mainly sedentary carnivorous ciliate of comparable weight.