en aquaculture aquaculture پژوهشي Orginal research papers The present study investigates the effects of varying levels of dietary fermented <em>Aspergillus oryzae </em>(0 g Kg^-1 as control group, 10, 20 and 30 g Kg^-1) on performance and haemato-immunological indices of common carp (<em>Cyprinus carpio</em>) fingerlings. Common carp fingerlings (n=240, w=4.56<span dir="RTL">&plusmn;</span>0.17 g) were supplied, randomly stocked in 12 aquaria and fed with experimental diets for 7 weeks. The results revealed no significant differences between performance parameters of fermented <em>A. oryzae </em>fed test and control diets (<em>p</em>˃0.05). Also, evaluation of haematological parameters (RBC, Hct, Hb) and white blood cell (WBC) counts showed no notable changes between experimental groups (<em>p</em>˃0.05). However, respiratory burst activity was meaningfully higher in fish fed fermented <em>A. oryzae</em> compared to control group (<em>p</em><0.05). The present results showed that possible effects of administration of fermented <em>A. oryzae</em> on immune responses in carp fingerlings. Diet, Fish immunology, Hemato-immunological indices, Prebiotic 1749 1756 http://jifro.ir/browse.php?a_code=A-10-452-3&slc_lang=en&sid=1 S.A. Hedayati hedayati@gau.ac.ir 100319475328460035532 100319475328460035532 Yes Gorgan University of Agricultural Sciences and Natural Resources T. Bagheri 100319475328460035533 100319475328460035533 No Offshore Fisheries Research Center, Iranian Fisheries Science Research Institute, Agricultural Research Education and Extension Organization, Chabahar, Iran S.H. Hoseinifar 100319475328460035534 100319475328460035534 No Gorgan University of Agricultural Sciences and Natural Resources H. Van Doan 100319475328460035535 100319475328460035535 No Department of Animal and Aquatic Sciences, Faculty of Agriculture, Chiang Mai University, Chiang Mai 50200, Thailand