Epsilon Archive for Student Projects

Abstract

Laboratory experiments were conducted to study the importance of polyunsaturated fatty acids (PUF A), in particular eicosapentaenoic acid (EPA, 20:5ro3), for growth, development, and fecundity of the detrivorous midge Chironomus riparius. Larvae were fed Tetraphyll®, a commercial fish food, oatflakes, and the cyanobacteria Spirulina sp. Tetraphyll® is rich in the essential fatty acids of the ro3- and ro6- families and contains modest concentrations of EPA (PUF A content 36% ). Oatflakes are rich in linoleic acid (18:2ro6) and relatively poor in a.-linolenic acid (18:3ro3) (PDFA 44%) and lack long­chain (>20 C) PDFAs. Spirulina, in contrast, contains y-linolenic acid (18:3ro6) and low concentrations of EPA (PUF A 21 % ). Additionally, feeding experiments were conducted with the green alga Scenedesmus obliquus (rich in 18:3ro3, poor in 18:3ro6, but lacking EPA, PDFA 47%), and with artificially EPA-supplemented Scenedesmus. Experimental endpoints were larval and adult size, survival, fatty acid composition of larvae, development rate, and fecundity.
Growth rates of larvae were affected both by food type and food concentration for Tetraphyll®, oatflakes and Spirulina, but only by food concentration for Scenedesmus and EPA-supplemented Scenedesmus. Highest growth rates were reached in the Tetraphyll®, oatflakes and Spirulina treatments. Growth was not improved with supplementation of Scenedesmus with EPA. In larval bodies, palmitic acid (16:0), palmitoleic acid (16:lro7) and linoleic acid (18:2ro6) were the dominant fatty acids. Adult midge size showed strong positive relationship with food concentration in treatments with Tetraphyll® (r=0.97), oatflakes (r=0.98) and Spirulina (r=0.93) whereas no relationship was found between fecundity and food type.
The FA analysis of larval bodies showed that Chironomus is able to synthesise long­chain PDF A from shorter precursor FA and that the conversion capacities apparently meet their physiological demands. The results also showed that even at low concentrations Chironomus growth is apparently not limited by the absence oflong-chain PDF A, thereby contradicting results from zooplankton studies.