Ching-Fong Chang

Annual cycle of gonadal histology and steroid profiles in the juvenile males and adult females of the protandrous black porgy, Acanthopagrus schlegeli

Abstract The objectives were to investigate the changes in gonadal histology and plasma levels of gonadal steroids from the bisexual to the male phase in the juvenile male black porgy, Acanthopagrus schlegeli . The reproductive cycle in the adult females was also studied. The gonad consisted mainly of testicular tissue at 5 months of age. The ovarian tissue in the stage of primary oocytes was well developed at 7 months of age. The gonad underwent an intensive spermatogenesis at 9 months of age. During the first and second spawning season, the testicular tissue was dominant, which made the fish male. The ovarian tissue became dominant at 18 months of age during the non-spawning season. The chronological order of histological features in black porgy was suggested to be testicular, bisexual, male, bisexual, male, and female. Maximum plasma levels of estradiol-17β and testosterone occurred simultaneously before the first spawning season in juvenile males and might have an important function in spermatogenesis. For females, gonadosomatic index, oocyte diameter, and levels of estradiol-17β and testosterone increased during the spawning season. Peak levels of progesterone and 17α-hydroxyprogesterone were not observed in juvenile males and adult females during the spawning season.

Estradiol-17β stimulates aromatase activity and reversible sex change in protandrous black porgy, Acanthopagrus schlegeli

The objective was to investigate the effects of estradiol-17β (E2) on gonadal development, spermiation, gonadal aromatase activity, and the concentrations of plasma sex steroids and vitellogenin in 2-year-old protandrous black porgy, Acanthopagrus schlegeli. Black porgy were divided into two groups, one fed a control diet and the other a diet mixed with E2 (4.0 mg/kg feed) for 4½ months. Significantly lower GSI was observed in the E2 group. Fish treated with E2 showed completely suppressed spermiation, and 38% had developing vitellogenic oocytes in the gonad (an evidence of sex reversal in 2-year-old fish). Higher gonadal aromatase activity and plasma E2 concentrations and lower concentrations of plasma 11-ketotestosterone (11-KT) were observed in the E2 group. After finishing 4½ months of E2 treatment in the early spawning season, the gonadosomatic index increased and spermiation resumed in the E2 group (which was fed a control diet) during the mid- or late-spawning season. Steadily increasing levels of plasma T and 11-KT and decreasing gonadal aromatase activity and plasma vitellogenin concentrations were observed in the E2 group. The present data show that E2 induced a temporary and reversible sex change (only a small proportion of the fish). Elevated aromatase activity in gonads, elevated E2 levels in plasma, and diminished levels of plasma 11-KT are associated with the occurrence of sex reversal in protandrous black porgy. J. Exp. Zool. 280:165–173, 1998.

The concentrations of plasma sex steroids and gonadal aromatase during controlled sex differentiation in grey mullet, Mugil cephalus

Abstract The objective of the study was to investigate plasma levels of sex steroids and gonadal aromatase activity during the period of controlled sex differentiation in grey mullet, Mugil cephalus . Six-month-old juvenile grey mullet were divided into three groups, control ( n =100), ethynyloestradiol (EE 2 , n =100) and 17α-methyltestosterone (17α-MT, n =100), respectively. EE 2 and 17α-MT groups were fed diets containing 20 mg EE 2 and 20 mg 17α-MT/kg of feed, respectively, for 4 months (from June 25 to October 25, 1993). The majority of control fish (70%) were still at the undifferentiated stage after 4 months of experiment. By contrast, after 2 months of EE 2 and 4–5 months of 17α-MT treatments, all the fish had differentiated into females and males, respectively. Plasma testosterone (T) remained low over the first 4-month period and gradually increased later in the control group. Plasma T was significantly higher in the EE 2 group in August after 2 months of treatment and in 17α-MT group in October after 4 months of treatment compared to the controls. Low levels of plasma oestradiol-17β (E 2 ) ( 2 group than in the other two groups. However, gradual increases of plasma 11-KT levels were observed in all three groups during the experimental period. Gonadal aromatase activity in the EE 2 group was significantly higher than in the 17α-MT and control groups from July to November. These data indicate that the concentrations of plasma T and gonadal aromatase activity are closely correlated with the development of controlled sex differentiation in grey mullet.

Hepatopancreas is the likely organ of vitellogenin synthesis in the freshwater prawn, Macrobrachium rosenbergii

The objective of the present study was to investigate the source of vitellogenin in the freshwater prawn, Macrobrachium rosenbergii. Ovarian development of M. rosenbergii was classified into five stages (stage I-V). Vitellin/vitellogenin was detected in the ovary and the hepatopancreas in different stages by native-PAGE and Western blotting. Two and three subunits of vitellin were observed in the ovary at the early- (I-II), mid- and late- (III-V) stages, respectively. The subunit of vitellogenin was not detected in the hepatopancreas at different stages of prawns. Hepatopancreas had positive immunocytological staining (against vitellin antibody) in different ovarian stages of prawn. Only vitellogenic oocyte but not previtellogenic oocytes and follicle cells had a positive immunocytological staining. Hepatopancreas could synthesize radiolabeled immunoreactive proteins after incubation with radiolabeled glycine on the basis of immunoprecipitation (against vitellin antiserum). Therefore, it is concluded that hepatopancreas is the most likely organ to synthesize vitellogenin in the freshwater prawn, M. rosenbergii.

Effects of LHRH-A and HCG on the steroid profiles of bisexual and mature male and female protandrous black porgy, Acanthopagrus schlegeli

Abstract The major objective was to investigate plasma steroid profiles after stimulation with LHRH-A or HCG during the bisexual, mature male and female phases in black porgy, Acanthopagrus schlegeli, a marine protandrous hermaphrodite. The responses of milt volume and oocyte diameters were also studied. Two-year-old black porgy during the non-spawning (bisexual stage) and spawning season (male phase), and wild-captured mature females, were injected with a superactive analogue of mammalian luteinizing hormone releasing hormone (LHRH-A) and human chorionic gonadotropin (HCG). Plasma samples were taken from fish before and after injection. Milt volume and oocyte diameters were also measured in mature males and females. Plasma testosterone in the bisexual and mature male phase increased significantly after treatment with LHRH-A or HCG. Plasma estradiol-17β and testosterone also increased in mature females after treatment. Peak levels of plasma testosterone occurred earlier in the mature male phase than in the bisexual stage. Spermiation and oocyte maturation were also stimulated during the spawning season after injection of LHRH-A and HCG. Peak levels of plasma progesterone and 17α-hydroxyprogesterone were not found after stimulation.

Stimulation of ovulation in ayu, Plecoglossus altivelis, by treatment with antiestrogens and luteinizing hormone-releasing hormone analog

Abstract The objectives of this study were to investigate the negative feedback effects of estrogen in ayu, Plecoglossus altivelis , by treatment with enclomiphene (cis-clomiphene), zuclomiphene (trans-clomiphene), clomiphene and LHRH analog (D-Ala 6 , des-Gly 10 LHRH ethylamide) based on ovulation and plasma steroid levels. Ovulation was stimulated in some fish by enclomiphene and clomiphene. The majority of ayu injected with LHRH analog ovulated. Injection of enclomiphene or clomiphene al 20 mg/kg wt induced a better ovulation response than 2 mg/kg wt. Enclomiphene increased plasma levels of estradiol-17β (E 2 ) and testosterone (T) at both dosages. In contrast, plasma T and E 2 levels increased significantly at the high dose of clomiphene. Only one fish (3%) ovulated and no increase of plasma steroids was observed in the zuclomiphene group. Enclomiphene seemed to have antiestrogenic potency. Negative feedback inhibition of estrogen in mature female ayu is therefore suggested.