The oxygen consumption of Theodoxus fluviatilis (L.) and Potamopyrgus jenkinsi (Smith) in brakish and fresh water

Abstract

1) Theodoxus fluviatilis and Potamopyrgus jenkinsi are present both in brackish and fresh water. Apparently T. fluviatilis has immigrated into fresh water in the early interglacial period, while P. jenkinsi at the end of the nineteenth century has migrated from brackish to fresh water. P. jenkinsi was for the first time observed in fresh water in Denmark in 1945. 2) T. fluviatilis and P. jenkinsi are unable to keep up a constant oxygen consumption when the oxygen percentage of the water is falling; the oxygen consumption decreases as soon as the oxygen content in the surrounding water falls, (Fig. 2, 3, 4 and 5). 3) The oxygen consumption for T. fluviatilis and P. jenkinsi at different temperatures agrees with Krogh's curve. T. fluviatilis from fresh water follows the curve up to c. 29° C, while the brackish water animals go up to c. 35° C, whereupon the oxygen consumption decreases rapidly. P. jenkinsi follows the curve up to c. 29° C and 32° C for brackish and fresh water animals respectively, whereupon the oxygen consumption shows a rapid decrease (Figs. 6 and 7). 4) T. fluviatilis has the same oxygen consumption whether it lives in brackish water (11.1% salinity) or in fresh water. P. jenkinsi from brackish water has, however, a greater oxygen consumption than the animals living in fresh water, (Figs. 8 and 9). The most probable cause of these conditions is discussed.