Abstract: Exposure to the external aqueous environment enhances the suscep tibility to infectious diseases in fish gills. Tounderstand the mechanism of local innate immunity against infectious grass carp reovirus(GCRV) in the gills, we identified the partial cDNA sequence ofM x, an antiviral effectormolecule, in rareminnow Gobiocypris rarus. Realtime quantitative RTPCR (qRTPCR) was emp loyed to quantitate mRNA levels of a pattern recognition recep tor, Tolllike receptor 3(TLR3), and type I interferons indicatormoleculeM x. The artificial infection experiments revealed that TLR3 andM x mRNA exp ressions were simultaneously significant upregulation at 1h postinjection (p0.05), and the M x mRNA exp ression kep t at high transcrip tion level till moribund (p<0.05). These results highlighted the importance of the gills as a tissue capable ofmounting a local immune response, and the interferon pathway was activated to GCRV infection.