SEASONAL-CHANGES OF GONADAL HISTOLOGY AND SERUM STEROID-HORMONE LEVELS IN THE BAMBOOLEAF-WRASSE PSEUDOLABRUS-JAPONICUS

Seasonal gonadal development and changes in serum sex steroid hormone levels were investigated in female and secondary male bambooleaf wrass e, 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 20 beta-S levels increased only during the spawning sea son (1,560 pg/ml), but 17,20 beta-P showed high and constant levels (4 50-850 pg/ml), suggesting that 20 beta-S may be involved in final oocy te maturation. The serum level of 11-KT in the secondary males showed a positive correlation with the testicular development; it peaked (2,9 30 pg/ml) in August when spermatogenesis actively proceeded, but decre ased during the spawning season (960-1,300 pg/ml) when spermiation occ urred. Serum 17,20 beta-P in the secondary males fluctuated at low lev els (160-420 pg/ml) throughout the experimental period.