Incorporation of [1‐14C] acetate into fatty acids of the crustaceansDaphnia magna andCyclops strenus in relation to temperature

Daphnia magna andCyclops strenus were maintained in aquaria containing sodium [1‐14C] acetate and the effect of temperature on labeling of their lipids was investigated. Incorporation of radioactivity in total lipids was slowed by a factor of 4 in cold‐exposed (5C) specimens compared to those incubated at 25 C. There was no significant difference in the distribution of label in the lipid classes of animals incubated at the two extreme temperatures. Decrease of the temperature from 25 to 5 C brought about a considerable reduction in the formation of palmitic and stearic acids and an increase in labeling of monounsaturated (18∶1) fatty acids inD. magna. Docosapolyenoic acids were absent from lipids of this crustacean.C. strenus directed a higher proportion of radioactivity into both oleic and docosahexaenoic acids upon cold exposure. In response to decrease of the temperature,D. magna formed a less unsaturated fatty acid population, as judged from dpm ratios of total saturated to total unsaturated fatty acids, thanC. strenus. Inability to form and accumulate docosapolyenoic fatty acids byD. magna might be related to their poor survival at reduced temperatures.