Weers, P.M.M., R.D. Gulati
Abstract:
The importance of fatty acids for growth and development for Daphnia galeata was investigated using algal diets varying in fatty acid composition. The quality of the algae was tested in life-history experiments. We found that Chlamydomonas reinhardtii was rich in polyunsaturated fatty acids with an acyl chain length of 16 and 18 carbon atoms. Changes in the degree of unsaturation of algal fatty acids, in response to P- and N-limited growth conditions, were not responsible for differences in algal food quality for D. galeata. Cryptomonas and Rhodomonas, algae species rich in poly-unsaturated fatty acids (PUFAs) with a carbon chain length of 20 and 22 (mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)), were of a higher quality than green algae. Addition of PUFAs in the form of emulsion particles, which included 30% EPA and DHA, to a diet composed of Scenedesmus acutes led to an improvement of algal food quality. On the other hand, daphnids fed with a mixture of Scenedesmus algae and emulsion particles composed of low quality fatty acids (myristic, palmitic and oleic acid) resulted in a lower nutritional value of the food. Even though we did not find Scenedesmus and Chlamydomonas to contain EPA or DHA, daphnids were able to develop normally on a diet composed of these algae. Therefore, we belief that C20 and C22 PUFAs are not essential compounds in the algal diet of the daphnids in spite of the stimulatory effect of these C20/22 PUFAs.
(Netherlands Institute of Ecology, Centre for Limnology, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands)