水温23-25°Cで飼育した雌walking catfish Clarias batrachusにおける成熟度の変化

抄録

To investigate the changes in ovarian maturity in the tropical walking catfish, 15 females and 15 males (7 months old) were maintained under constant warm water temperature (23-25°C) and natural photoperiod until the age of 31 months old. Blood and ovarian oocytes were sampled monthly. Histological observation of the oocytes revealed that 10-31 months old females always possessed mature oocytes which had completed vitellogenesis. However, the percentages of mature oocytes fluctuated and atretic oocytes were also observed. No spontaneous ovulation or spawning occurred during the experiment. However, all females which had received a human chorionic gonadotropin (HCG) injection (0.8 IU/g BW) had succeeded in ovulation by the end of the experiment. Plasma estradiol-17β and testosterone started to increase at 8 months old, and there-after fluctuated at high levels. However, testosterone levels became higher in 2-year-old fish than did those in yearling fish. 17α-hydroxyprogesterone (17α-P) levels also fluctuated, but average levels were lower than those of estradiol-17β and testosterone. Plasma 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-P) and progesterone were below detectable limits. These results indicate that female walking catfish can maintain conditions of maturity for an extended period under warm water and natural photoperiod.