Studies on the survival of the rotifer philodina after freezing and thawing

Abstract

Summary The survival of the rotifer Philodina after freezing and thawing has been examined under a variety of experimental conditions. Particular emphasis was placed on obtaining maximum survival by employing the most advantageous combination of protective additive concentration and cooling rate. Glycerol is an effective cryoprotective agent in this system at concentrations as low as 1% and exerts a maximum protective influence at a concentration of 2 to 3%. Glycerol solutions in the range of 5 to 10% result in somewhat anomalous survival curves as a function of cooling rate, although survival at these concentrations is moderately high at the extremes of the “slow cooling” range. Treatment of rotifers with a 20% glycerol solution results in death; thus, it is possible that sublethal toxic effects play a role at lower glycerol concentrations. Cooling rate optima appear in the region of 3 to 5°C per min with deviations occurring at high levels of glycerolation. Survivals of the order of 50 to 60% can be routinely achieved by employing the most suitable pretreatment and cooling rate. Animals frozen in this manner have been stored up to 20 days at liquid nitrogen temperatures without a noticeable decline in viability. In addition to manifesting normal swimming and feeding habits, survivors of freezing appear to enjoy a normal life span and reproductive capacity.