A YY male goldfish from mating estrone-induced XY female and normal male.

A YY male of the goldfish, Carassius auratus, was detected among offspring of an estrone-induced XY female mated with a normal XY male. There is convincing evidence of the reality of inversion of sex differentiation in the XY zygote by estrone as well as male heterogamety (hence, female homogamety) in the goldfish.