TheSTAT5(signal transducer andactivator of transcription 5) genewas isolated and characterized froma round-spotted pufferfish genomic library. This gene is composed of 19 exons spanning 11 kb. The full-length cDNA ofTetraodon fluviatilis STAT5(TfSTAT5) contains 2461 bp and encodes a protein of 785 amino acid residues. From the amino acid sequence comparison,TfSTAT5 is most similar to mouse STAT5a and STAT5bwith an overall identity of 76% and 78%, respectively, and has