Seasonal observations on the plasma, red cell, and blood volumes of two turtle species native to Ontario.

Abstract

Two turtle species, Graptemys geographica and Chelydra serpentina were studied. The animals were obtained in the Kingston, Ontario area and maintained in the lake from which most of them had been taken. T-1824 and 51Cr were used to determine plasma and erythrocyte volumes respectively. In vitro and in vivo tests established that these methods were satisfactory, but mixing times in these poikilotherms were longer than mixing times in mammals. In G. geographica, plasma volume showed seasonal variations. The mean plasma volume in winter was 77.8 ml/kg, a volume significantly lower than the summer mean of 106.7 ml/kg. There was no significant seasonal variation in red cell volume; the mean for all seasons was 18.1 ml/kg. In this species lower plasma volumes resulted in significantly lower blood volumes during the winter. Evidence is presented in support of the concept that in G. geographica, in winter, an appreciable volume of plasma is sequestered and not available to the general circulation. In C. serpentina plasma volume was significantly lower than in the other species but there were no significant seasonal variations. For all seasons mean plasma volume was 65.7 ml/kg and mean erythrocyte volume was 18.5 ml/kg.