Effect of season on oocyte development and serum steroid hormones in LHRHaand pimozide-injected catfish Clarias macrocephalus (Gunther)

Oocyte and blood samples were taken from gravid female catfish Clarias macr ocephalus at 4-h intervals to monitor the stage of oocyte development and s erum steroid hormone profiles after injection of luteinizing hormone-releas ing hormone analogue (LHRHa) and pimozide (PIM) during the off-season (Febr uary) and the peak of the natural breeding period (August). Results showed that the onset of final oocyte maturation (12 h) and ovulation (16 h), and levels of serum estradiol-17 beta (E-2) did not vary with season in LHRHa+P IM-injected fish. In February, ovulated eggs were stripped from three and t wo hormone-treated fish at 16 h and 20 h post-injection, respectively. In A ugust, ovulation was observed in all hormone-treated females (n=5) at 16 h post-injection but stripping of the eggs was possible only 4h thereafter. S erum E-2 levels were significantly different only with varying time post-in jection; a marked increase occurred at 12 h, but the elevation was higher i n fish induced to ovulate during the peak (16.8 ng/ml) than off-season (7.7 ng/ml). Hormone-treated fish showed higher serum testosterone (T) levels d uring the peak season (17-23 ng/ml) than those injected during the off-seas on (10-20 ng/ml) at 4-12 h post-injection. Serum 17 alpha,20 beta-dihydroxy -4-pregnene-3-one (DHP) levels of hormone-treated fish during the off-seaso n were only about half the level (0.29 and 0.52 ng/ml) of those treated wit h the same hormones during the peak season (0.54 and 0.9 ng/ml) at 8 and 12 h post injection, respectively. Development of oocytes and serum steroid h ormone profiles after LHRHa+PIM-induced ovulation provide basic understandi ng of the processes that mediate final oocyte maturation and ovulation in c aptive C. macrocephalus.