The effects of testosterone implants on ovarian morphology in the bluehead wrasse, Thalassoma bifasciatum (Bloch) (Teleostei: Labridae)

Abstract

The effects ofexogenous testosterone pellet implantsat 21 and 40days on the ovary of Thalassoma hifasciaturn, a protogynous marine fish, are described. The characteristic markings of the terminal blue phase appeared by 4 to 5 days and were complete by 18 days. There was no shift in sex ratio in the treated fish when compared to an untreated control group. None of the ovaries showed signs of precocious transformation, i.e., spermatogenic tissue was lacking, and there was no evidence of duct formation. Instead, however, the ovaries of the treated fish showed marked degenerative changes characterized by oocyte breakdown, fat infiltration, vacuolization, the accumulation of fibrous PAS+ material and the appearance of small eosinophilic cells.These findings conflict with earlier studies on the same organism that employed different procedures. However, they resemble more closely the results obtained from work on another protogynoid, the ricefield eel, Monoprerus afbus. They add new light on the role of sex hormones in the reversal process of T. bifasciaturn and hermaphroditic fishes in general.

Gonadal structure and P450scc and 3?-HSD immunoreactivity in the gobiid fish Trimma okinawae during bidirectional sex change

“…However, a testosterone implant in females failed to induce the development of male tissues in Monopterus albus and Thalassoma duperrey (Tang et al, 1974;Kramer et al, 1988). These results suggest that testosterone productivity is important for development of female tisuues.…”

Estradiol-17? suppresses testicular development and stimulates sex reversal in protandrous black porgy, Acanthopagrus schlegeli

“…The E 2 to androgens ratio also significantly increased during the course of sex reversal in the protandrous anemonefish, Amphiprion melanopus (Godwin and Thomas 1993). However, administration of androgens failed to induce a functional sex change in the protogynous ricefield eel, Monopterus albus and bluehead wrasse, Thalassoma bifasciatum (Tang et al 1974;Kramer et al 1988). The physiological importance of a decrease in androgens such as 11-KT in the sex reversal of protandrous black porgy is still unclear.…”

Sex-change and gonadal steroids in sequentially-hermaphroditic teleost fish

“…In some species, T concentrations are relatively independent of sexual stage, thus suggesting that T is not directly involved in the transition (Nakamura et al, 1989;Cardwell and Liley, 1991;Guiguen et al, 1993). However, the administration of T and (or) T derivatives can induce sex-change in some protogynous species (Kuo et al, 1988;Tan-Fermin et al, 1994;Lee et al, 1995;Hassin et al, 1997;Glamuzina et al, 1998;Yeh et al, 2003), but not in others (Kramer et al, 1988;Kroon and Liley, 2000). In estuary grouper (Epinephelus coioides), small doses of T and T derivatives promoted ovarian development (Yeh et al, 2003), while in bluehead wrasse (Thalassoma bifasciatum), T or 5a-dihydrotestosterone induced ovarian degeneration (Kramer et al, 1988).…”

“…Since that time the number of studies investigating the relationship between sex-change and steroids has increased, as has the number of hypotheses about this relationship. Research has also expanded to include both the 'downstream' effects of steroids on reproductive tissues during sex-change (Kramer et al, 1988;Nakamura et al, 1989), and the 'upstream' brain and pituitary activities that affect subsequent steroid biosynthesis (reviewed by Grober, 1998;Bass and Grober, 2001).…”