Interactions of hormones and gonadal development of Tilapia aurea fry

Abstract

Gonadal differentiation of Tilapia aurea fry reared under various photoperiods was studied. Histological sections were made of fry gonads from the first free-swimming day through day 20 from samples taken every other day. Three feeding treatments were used for each photoperiod: no hormone, 17-[alpha]-ethynyltestosterone, and 17-[alpha]-ethynyl-estradiol. Statistical analyses show no significant difference in percent of differentiated and non-differentiated fry among the photoperiods. There also was no significant difference in size of fry for each feed treatment among the photoperiods. Fry treated with 17-[alpha]-ethynylestradiol initiated differentiation four days earlier than females not receiving hormone. Males fed 17-[alpha]-ethynyltestosterone initiated differentiation two days earlier than non-hormone treated fry. There was no significant difference in percent of differentiated to non-differentiated fry by age but there was a significant difference in size by age. Differentiated fry were significantly larger than non-differentiated fry. Fry treated with 17-[alpha]-ethynyltestosterone were significantly larger than male fry not receiving the hormone and females, which included both those fed 17-[alpha]-ethynylestradiol and those not given this hormone. Females fed 17-[alpha]-ethynylestradiol were not significantly different in size from females not receiving the hormone.