Abstract:
Changes in the peptide levels of sea bream (Sparus aurata) GnRH (sbGnRH) in the olfactory bulb, telencephalon including the preoptic area, hypothalamus, optic tectum-thalamus and pituitary during a reproductive cycle were investigated in addition to plasma levels of testosterone (T), 17β- estradiol (E2) and 17α, 20b-dihydroxy-4-pregnen-3-one (DHP) in wild female Asian sea bass Lates calcarifer in Nha Phu lagoon, Vietnam from March to September, 2010. Ovaries were classified into five stages: II Recovering spent (March -April), III Maturing (May-June), IV Mature (June), V Ripe and ovulating (July- August) and VI Spent (September). The gonadosomatic index increased significantly from the stage II (1.62%±0.12) to stage V (8.48%±0.23) and dropped thereafter in stage VI (2.05%±0.25). In the olfactory bulb and telencephalon, sbGnRH levels in stage IV and stage V were slightly higher than those in the other stages, but no significant differences in sbGnRH levels were found among the ovarian stages. In the hypothalamus and optic tectum-thalamus, although significant differences in sbGnRH level were not found among the ovarian stages, the highest level of sbGnRH was determined in stage III (594.13±152.12 pg tissue-1 and 501.37±124.35 pg tissue-1, respectively). In the pituitary, sbGnRH level in stage III (6927.03±218.92 pg tissue-1) was significantly higher than that in the other stages. In addition, plasma T, E2 and DHP levels increased significantly during ovarian maturation or ovulation with the highest level of T (2.91±0.31 ng ml-1) and E2 (4.98±1.43 ng ml-1) recorded in stage IV and DHP (389.6 ± 136.03 pg ml-1) in stage V. The results showed that sbGnRH in the anterior brain and pituitary is involved in initiation and ovarian maturation in wild Asian sea bass.
