NUTRITIONAL SUITABILITY OF SOME UNIALGAL DIETS FOR FRESH-WATER CALANOIDS - UNEXPECTED INADEQUACIES COMMONLY USED EDIBLE GREENS AND OTHERS

1. Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Trop odiaptomus spectabilis) were measured on mono-specific diets of compar ably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas s p., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capric ornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17 degrees C) and food supply lev el (1 mg Cl-1). 2. All diets other than Scenedesmus and Selenastrum su pported complete naupliar development at broadly comparable times with in and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between d iet types, and both Chlamydomonas and Cyclotella were inferior or inad equate for copepodid development. 3. Both naupliar and copepodid stage s ingested radiolabelled Scenedesmus and Selenastrum readily. Comparat ive incorporation rate measures of Selenastrum and Cryptomonas respect ively exceeded estimated metabolic maintenance needs of stage 3/4 naup lii of T. spectabilis by some 56% and 790%. Scope for growth ('surplus ' energy) was accordingly fourteen-fold greater on Cryptomonas than on Selenastrum/Scenedesmus. The dietary inadequacy of these two green al gae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.