| This study established the maturational time line for Brienomyrus niger and identified discrete developmental stages, characterized by the appearance of prominent osteological sexual dimorphisms (support structures of the anal-fin). The study proceeded with an investigation of androgen-induced transformations in juvenile and adult fish. 17alpha-methyltestosterone (17MT) exposure induced male-typical transformations of reproductive structural and behavioral traits in juveniles of both sexes and in subadult and adult females. These transformations were partial and masculinized only secondary sexual traits: (1) large expansions of the anal fin ray bases and thickening of fin ray shafts, (2) inferred increases in attached muscle leading to an indentation of the dorsal margin of the anal fin, (3) structural modifications of the electric organ, i.e. a thickening of the anterior face of the individual electrocytes, and (4) temporal changes in the electric discharge it generates. Following hormone withdrawal, osteological modifications remained permanent, whereas the male-typical elongation of the electric organ discharge and body wall indentation returned to pre-treatment conditions. 17MT treatment did not masculinize female gonads, but, on the contrary, resulted in a dramatic hypertrophy of gonadal tissue in females and induction of normal oocytic development. There was no evidence of intersex gonads. |
