Effects of mammalian gonadotropin‐releasing hormone analogue, pimozide, and the combination on plasma gonadotropin levels in different seasons and induction of ovulation in female catfish

Abstract

In the catfish Heteropneustes fossilis, 0.5μg g‐1 B.W. mGnRH‐A alone or the low dose of 0.05 μg g‐1 B.W. in combination with pimozide [a dopamine (DA)‐receptor antagonist, 5 or l0μg g‐1 B.W.], caused a preovulatory surge in plasma gonadotropin (GTH) and induced a high rate of ovulation. The ovulatory response of the catfish to the low dose of mGnRH‐A when given alone was not effective in the early (July) but was effective in the late spawning season (August). Plasma GTH response to these treatments showed seasonal variations. Pimozide administration potentiated the response to mGnRH‐A in a season‐dependent manner, being effective only in the prespawning and spawning phases. Pimozide treatment alone did not affect plasma GTH. These observations suggest that the release of GTH from the pituitary is subject to seasonal differences in the sensitivity of the GnRH system and the degree of its modulation by dopamine.