Can fish change their gender?
this actually occurs in some species, it is mainly known from some marine fish, e.g. several wrasses and the well known clownfish. In case of the latter, all fry are born as males, and the strongest specimen then turns into a female.
There are still different views concerning livebearing toothcarps (swordtails in particular). There are both experts who are sure that this exists (in that case from female to male) and ones who contradict it.
Dr. Bodo Schnell