Seasonal changes of gonadal histology and serum steroid hormone levels in the bambooleaf wrasse Pseudolabrus japonicus

Abstract

Seasonal gonadal develpment and changes in serum sex steroid hormone levels were investigated in female and secondary male bambooleaf wrasse, Pseudolabrus japonicus, from Ago Bay in Mie Prefecture from May to December 1991. Seasonal changes of GSI and gonadal histology indicated that the gonadal maturation occurred during October and November. In females, serum 20β-S levels increased only during the spawning season (1,560 pg/m/), but 17,20β-P showed high and constant levels (450-850 pg/ml), suggesting that 20β-S may be involved in final oocyte maturation. The serum level of 11-KT in the secondary males showed a positive correlation with the testicular development; it peaked (2,930 pg/ml) in August when spermatogenesis actively proceeded, but decreased during the spawning season (960-1,300 pg/ml) when spermiation occurred. Serum 17,20β-P in the secondary males fluctuated at low levels (160-420 pg/ml) throughout the experimental period.