Rapid-freeze preservation minimizes radioisotope leakage from zooplankton in feeding experiments
Preservation of labelled zooplankton by rapid freezing on dry ice minimizes loss of CI4 and P32. C14 retention in frozen samples approximates 100\% even after 24 h storage. This is a major improvement over retention in chemical preservatives such as ethanol. Isotope loss in ethanol is rapid (on a time scale of minutes) and extensive (up to 72\%). P32 appears to be more labile than C14, and exposure of labelled animals to liquids must be minimized to effectively conserve this isotope. P32 retention is then improved, but may vary between 75 and 100\%. We urge continued caution in feeding experiments using P32, especially when dual labeling to measure selectivity.