Effects of Long-Term Testosterone, Gonadotropin-Releasing Hormone Agonist, and Pimozide Treatments on Gonadotropin II Levels and Ovarian Development in Juvenile Female Striped Bass (Morone saxatilis)1

The ability of the juvenile female reproductive axis to re-spond to hormonal stimulation was investigated in a Perciform fish, the striped bass (Morone saxatilis) using various combina-tions of testosterone (T), GnRH agonist (GnRHa), and pimozide. A long-term treatment with T alone, or T in combination with GnRHa, increased pituitary gonadotropin II (GtH II) levels 2-and 3-fold, respectively, suggesting that T and GnRHa each stim-ulate GtH II accumulation. Release of the accumulated GtH II could be induced only by high doses of GnRHa in combination with T, indicating that GtH II synthesis and release require dif-ferent levels of GnRH stimulation. The addition of the dopamine antagonist pimozide did not affect pituitary and plasma GtH II levels but, in response to an additional acute GnRHa challenge, inhibited the release of GtH II. Although ovarian development was slightly stimulated by a combined T and GnRHa treatment, vitellogenesis was generally not initiated. The present study dem-onstrated that the juvenile striped bass pituitary is responsive to hormonal stimulation, resulting in elevated levels of GtH II in the pituitary and plasma. However, increased plasma levels of GtH II did not result in precocious puberty, suggesting that ad-ditional factors are required for the initiation of ovarian devel-opment in this teleost