Mixtures of microencapsulated lipids and Scenedesmus quadricauda grown at different degrees of P limitation were used as food for Daphnia galeata in two growth experiments. Thereby, food quality in terms of ω3‐fatty acid (ω3‐FA) or phosphorus (P) content could be assessed without interference from other factors. 2. ω3‐highly unsaturated fatty acids (ω3‐HUFA), given to Daphnia as fish oil or eicosapentaenoic acid (EPA) together with non P‐limited algae, decreased the time to first reproduction. When fed fish oil, somatic growth and survival were also enhanced. Linolenic acid also decreased the time to first reproduction but to a lesser extent than EPA. 3. Food quality depended to a large extent on the degree of P limitation of Scenedesmus , which is consistent with P limitation of Daphnia. The overall impact of P was always larger than the effect of ω3‐FA. Growth, survival and reproduction were elevated when Daphnia were fed non P‐limited Scenedesmus compared to treatments with P‐limited algae. 4. The relative importance of ω3‐HUFA and P content in the food changed over a C : P gradient, with stronger effects of ω3‐HUFA at low C : P ratios.
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Sundbom et al. (1997) studied this question.