Two major isoforms,with an insertion (+KTS) or exclusion (-KTS) in amino acid sequences,resulting from alternative splicing,were cloned from the gonad of rice field eel Monopterus albus by RT-PCR.The length of cDNA sequence of the two WT1 isoforms,WT1 (-KTS) and WT1 (+KTS),were 1 236 bp and 1 245 bp,respectively.The results showed that the amino acid sequences of WT1 (-KTS) and WT1 (+KTS) in M.albus shared 93.2% and 93.0% identity with WT1a in Epinephelus coioides respectively.They also contained highly similar zinc finger domains.The phylogenetic analyses showed that the two isoforms and WT1a of E.coioides were clustered in the same branch.The semi-quantization results revealed that high expression levels of WT1 gene can be found in gonads,kidney,intestine,spleen and heart.The real-time PCR results showed that WT1 gene was expressed at each stage of the gonad development,and the expression increased first and then decreased.