THE ROLE OF DIETARY FATTY ACID COMPOSITION FOR GROWTH, EMERGENCE, AND FECUNDITY IN CHIRONOMUS RIPARIUS.

W. Goedkoop¹, M. Hancke¹, and G. Ahlgren². ¹Dept. Environmental Assessment, Swedish Univiversiy of Agricultural Sciences, Uppsala, Sweden, ²Dept. of Limnology, Uppsala University, Uppsala, Sweden

Chironomus larval growth, emergence, adult size, and fecundity were determined in laboratory experiments with different diets. Experimental diets consisted of Tetraphyll® (rich in ALA and EPA), oatflakes (low ALA, lacking EPA), Spirulina (low ALA, low EPA), Scenedesmus obliquus (rich in ALA, lacking EPA), and EPA-enriched S. obliquus (rich in ALA and EPA) and were approximately equal in their carbon and nitrogen concentrations. Additionally, larvae were grown without food additions on a food-poor artificial sediment. At low food concentrations larval growth was higher on Tetraphyll® than on other food types. At high food concentrations no difference in growth were found among treatments with Tetraphyll®, oatflakes, and Spirulina, but larvae showed substantial lower growth on both Scenedesmus diets due to the lower digestibility of Scenedesmus cells. Growth and development in the food-poor artificial sediment was extremely low and neither ALA nor EPA was detected in larvae. These results show that Chironomus lacks the ability for de novo synthesis of ALA. However, Chironomus readily synthesized EPA from dietary ALA, even at low dietary levels. Both food type and food concentration affected adult size and emergence, indicating that the biochemical composition of food may have strong repercussions on sexual maturation and reproduction.