Gonadotropin-releasing hormone(GnRH)is a conservative neurodecapeptide family,which plays a crucial role in regulating the gonad development and in controlling the final sexual maturation in vertebrate.Two differing cGnRH-Ⅱ cDNAs of common carp,namely cGnRH-Ⅱ cDNA1 and cDNA2,were firstly cloned from the brain by rapid amplification of cDNA end(RACE)and reverse transcription- polymerase chain reaction(RT-PCR).The length of cGnRH-Ⅱ cDNA1 and cDNA2 was 622 and 578 base pairs(bp),respectively.The cGnRH-Ⅱ precursors encoded by two cDNAs consisted of 86 amino acids,including a signal peptide,cGnRH-Ⅱ decapeptide and a GnRH-associated peptide(GAP)linked by a Gly-Lys-Arg proteolytic site.The results of intron trapping and Southern blot showed that two differing cGnRH-Ⅱ genes in common carp genome were further identified,and that two genes might exist as a single copy.The multi-gene coding of common carp cGnRH-Ⅱ gene offered novel evidence for gene duplication hypothesis.Using semi-quantitative RT-PCR,expression and relative expression levels of cGnRH-Ⅱ genes were detected in five dissected brain regions,pituitary and gonad of common carp.With the exception of no mRNA2 in ovary,two cGnRH-Ⅱ genes could be expressed in all the detected tissues.However,expression levels showed an apparent difference in different brain regions,pituitary and gonad.According to the expression characterization of cGnRH-Ⅱ genes in brain areas,it was presumed that cGnRH-Ⅱ might mainly work as the neurotransmitter and neuromodulator and also operate in the regulation for the GnRH releasing.Then,the expression of cGnRH-Ⅱ genes in pituitary and gonad suggested that cGnRH-Ⅱ might act as the autocrine or paracrine regulator.