en aquaculture aquaculture پژوهشي Orginal research papers This study compared the efficacy of different diets on the population density, specific growth rate, doubling time, and fatty acids composition of the freshwater cyclopoid copepod <a name="OLE_LINK2"></a><a name="OLE_LINK1"><em>Acanthocyclops trajani</em></a>. The experimental diets consisted of fresh binary microalgae (<em>Scenedesmus obliquus</em>+<em>Spirulina maxima</em>), dry binary microalgae (<em>S. obliquus</em>+<em>S. maxima</em>), dry <em>Gracilaria corticata</em>, and mixed dry vegetables (including spinage, coriander, and parsley). Results have showed that the highest population growth rate (0.145), mean density (1445 ind L^-1), and the shortest doubling time (4.76 d) have been obtained in copepods fed on dry binary microalgal diet. The amounts of fatty acids in <em>A. trajani</em> could be modified by feeding copepod with different diets. The amount of C22: 6n-3 (DHA) was significantly higher in copepods fed dry binary microalgae (3.75&plusmn;1.08 %) compared to the other diets. This cyclopoid copepod had higher levels of EPA and DHA than those in corresponding diets, suggesting that the <em>A. trajani</em> is probably able to accumulate EFA (essential fatty acid). This study indicates the potential of using specifically dry microalgae to improve the nutritional composition in copepods as a suitable supplementary live food for freshwater fish larvae. Acanthocyclops trajani, Specific growth rate, Doubling time, Fatty acid, Live food. 1447 1462 http://jifro.ir/browse.php?a_code=A-10-3016-1&slc_lang=en&sid=1 R. Rahmati rahmati764@gmail.com 100319475328460034838 100319475328460034838 No Sari Natural Resources University A. Esmaeili Fereidouni sohrabesmaeili70@gmail.com 100319475328460034839 100319475328460034839 Yes Sari Natural Resources University A. Rouhi roohi_ark@yahoo.com 100319475328460034840 100319475328460034840 No Sari, farah abad, Caspian Sea ecology Institute N. Agh n.agh@urmia.ac.ir 100319475328460034841 100319475328460034841 No Urmia University