A microencapsulated analog of LH-RH accelerates maturation but without stimulating sex reversal in the protandrous black porgy, Acanthopagrus schlegeli.

Abstract

The objective of this study was to regulate the reproduction and levels of gonadal steroids in 3-year-old protandrous black porgy (Acanthopagrus schlegeli) by treatment with microencapsulated D-Trp6-luteinizing hormone-releasing hormone (LH-RH analog) during the prespawning season. Twenty-four previously male black porgy were equally divided into 2 groups and injected with vehicle (control group) or with microencapsulated LH-RH analog (LH-RH analog group), respectively. Spermiation and plasma levels of testosterone (T), estradiol-17 beta (E2) and 17 alpha-hydroxyprogesterone (17 alpha-OH P) were measured, after treatment, at intervals of 1-2 weeks for 4 months. Oocyte diameters were also measured after 4, 10, 12, 14 and 16 weeks of treatment. The microencapsulated LH-RH analog accelerated the onset of spermiation by at least 5 weeks. Oocyte diameters were also significantly increased in the LH-RH analog group. The microencapsulated LH-RH analog did not increase the number of sex-reversing females compared with the number in the control group. High levels of plasma E2 were found in the sex-reversing females in the LH-RH analog and control groups during the prespawning and spawning season. Low levels of plasma E2 were observed in the non-reversed males in both the LH-RH analog and the control groups. Similar profiles of plasma T levels were detected in male and in reversing female black porgy in the LH-RH analog and control groups. Plasma 17 alpha-CH P levels were low and constant throughout the experimental period in fish in each group. These findings indicate that the microencapsulated LH-RH analog accelerated gonadal maturation in the black porgy during the prespawning season. Plasma levels of E2 seem to be closely related to the occurrence of natural sex reversal in the protandrous black porgy, A schlegeli.