We have cloned a full length cDNA coding for activin β(B) subunit from the goldfish ovary. Sequence analysis of the goldfish activin β(B) shows that this peptide is extremely conserved across vertebrates. The mature region of goldfish activin β(B) has 93 and 98% amino acid identity with that of human and zebrafish β(B) subunit respectively. The identity of the cloned goldfish activin β(B) was further confirmed by expressing the protein in the Chinese hamster ovary (CHO) cells followed by detection of the specific activity of activin in the culture medium using F5-5 cell assay. mRNA of goldfish activin β(B) is expressed in a variety of goldfish tissues including ovary, testis, brain, pituitary, kidney and liver, suggesting a wide range of physiological roles for activin in the goldfish.