Effect of season on oocyte development and serum steroid hormones in LHRHa and pimozide-injected catfish clarias macrocephalus (Günther)

Abstract

Oocyte and blood samples were taken from gravid female catfish Clorias macrocephalus at 4-h intervals to monitor the stage of oocyte development and serum steroid hormone profiles after injection of luteinizing hormone-releasing hormone analogue (LHRHa) and pimozide (PIM) during the off-season (February) 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 β (E2) did not vary with season in LHRHa+PIM-injected fish. In February, ovulated eggs were stripped from three and two hormone-treated fish at 16 h and 20 h post-injection, respectively. In August, ovulation was observed in all hormone-treated females (n=5) at 16 h post-injection but stripping of the eggs was possible only 4 h thereafter. Serum E2 levels were significantly different only with varying time post-injection; a marked increase occurred at 12 h, but the elevation was higher in 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 during the peak season (17-23 ng/ml) than those injected during the off-season (10-20 ng/ ml) at 4-12 h post-injection. Serum 17α,20α-dihydroxy-4-pregnene-3-one (DHP) levels of hormone-treated fish during the off-season were only about half the level (0.29 and 0.52 ng/ ml) of those treated with 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 hormone profiles after LHRHa+PIM-induced ovulation provide basic understanding of the processes that mediate final oocyte maturation and ovulation in captive C. macrocephalus.