Ctenopharyngodon idella). The full-length cDNA was successfully cloned by RT-PCR and rapid amplification of cDNA ends (RACE). The full-length cDNA was 916 bp, consisting of a 735 bp open reading frame (ORF) encoding 244 amino acids, a 89 bp 5′untranslated region (5′ UTR), and a 92 bp 3′ untranslated region (3′ UTR). The molecular weight of this mature peptide was estimated to be 26 162.5U. Multiple alignment analysis revealed that grass carp C1qC shares the highest identity with zebrafish C1qC (71%). We constructed a phylogenetic tree using the neighbor-Joining (NJ) method. Grass carp were grouped most closely with zebrafish ( was significantly up-regulated in most tissues following challenge with grass carp reovirus (GCRV). The expression of expression differed during the various stages of embryonic development. Our results suggest that plays an important role in early embryonic development and in the response to GCRV-related diseases in grass carp. Our result provide a basis for further evaluation of the role of grass carp in immune function.