Effect of Oxygen Pressure on Swimming Activity of Ceriodaphnia Quadrangula

Abstract

The effect of oxygen pressure on the swimming activity of hemoglobin-rich (red) and hemoglobin-poor (pale) Ceriodaphnia quadrangula was studied at 25?C. The swimming time of red animals until final cessation of antennal movement was constant (38 min) in extremely low oxygen concentration, rapidly increased, and reached 100 min at 4.5 torr. The swimming time of pale animals was constant (24 min) at 3.5 torr, increased gradually, and reached 100 min at 11.7 torr. The swimming time of red animals in nitrogen-saturated water increased on exposure to 3.5 torr and reached a maximum of 35 min at 5.8 torr. The swimming time of pale animals increased above 10.5 torr and reached a maximum of 23 min at 16.3 torr. Hemoglobin commonly occurs in the hemolymph of Ceriodaphnia (Hoshi, 1957; Czeczuga, 1965; Kobayashi and Hoshi, 1983). As in many other cladocerans (Fox et al., 1949, 1953; Green, 1955; Kobayashi and Hoshi, 1982; Kobayashi and Nezu, 1986), the concentration of Ceriodaphnia-hemoglobin varies considerably with environmental oxygen concentration. Hemoglobin-rich (red) animals are normally found in water of low oxygen concentration, while hemoglobin-poor (pale) animals are found in well-aerated water (Czeczuga, 1965; Kobayashi and Hoshi, 1983). In general, the physiological function of hemoglobin in small invertebrates has been estimated from the reduction of oxygen consumption of animals after inactivation of their hemoglobin with carbon monoxide (Prosser, 1973; Weber, 1980). In cladocerans, pale animals have been used as natural controls for comparison with red animals, because of the marked difference in the hemoglobin concentrations between them (Kobayashi, 1974; Kobayashi and Gonoi, 1985). Functional significance of Ceriodaphnia-hemoglobin has been evaluated from the swimming distance in a glass tube (150 cm long) in pale, red, and carbon monoxide-treated red animals (Kobayashi and Yoshida, 1986). The swimming speed (43 cm/min) did not differ between pale and red animals. They both swam a distance of 5 m in oxygen pressure of 2.3 torr. At 4.7 torr, red animals swam more than 80 m, whereas pale animals swam only 7 m. Further increase in oxygen pressure induced an increase in the swimming distance of pale animals which reached 100 m at 21 torr. In red animals treated with carbon monoxide, oxygen pressures demonstrated almost the same effect on the swimming activity as in pale animals. Apparently hemoglobin allowed red animals to take up oxygen in low oxygen environment and to swim a longer distance than pale or carbon monoxide-treated animals even in low oxygen pressure. In oxygen-regulating animals, the critical oxygen concentration (below which the oxygen consumption depends on ambient oxygen concentration) has been determined, to study their responses to low environmental oxygen (Mangum and Van Winkle, 1973; Herreid, 1980; Lubbers, 1980). When the swimming distance was measured by the above-mentioned method (Kobayashi and Yoshida, 1986), the swimming distance was found to increase exponentially with an increase in oxygen concentration and even to exceed the upper limit of measurement. By the use of this method, therefore, it is not possible to estimate the oxygen concentration equivalent to the critical oxygen concentration.