Paramecium Ecology: Electromigration for Field Samples and Observations on Density

Abstract

Direct electric current can be used to extract paramecia from samples of mud and water. Oval plastic dishes, 17 x 5.5 x 3.2 cm, hold the samples. Specimens are protected from the wire leads with agar—filled U tubes, connected with the dish by glass siphons. A voltage drop of 1.75 to 3.0 volts between siphons is employed for 3 successive periods of 30 min each. The animals migrate to the cathode. Samples taken when the water is colder than 10 C are allowed to stand at room temperature for 2 hr before electromigration. The method is estimated to be around 95% efficient in removing present. A significant increase in abundance has been observed in the field during a period of 10 days when the water temperature remained at 4 C. The increase was comparable to what can be obtained in the laboratory at 5 C. The maximum density of paramecia (P. caudatum plus P. aurelia) observed was 12.5 per ml or 250 per cm 2 of surface. Other small invertebrates are amenable to collection by the electromigration technique, but not all species migrate equally well.