The present study was designed to investigate the in vivo dose-response of mammalian GnRH analogue [d-Ala6, Pro9, NEthylamide]-mGnRH in stimulating a pre-ovulatory LH surge and subsequent ovulation in female tench. Five doses of mGnRHa (1, 2.5, 5, 10, and 20 μg kg− 1) and a control group (0.9% NaCl) were tested under hatchery conditions. Concentration of plasma LH and ovulation success were evaluated. All mGnRHa treatments yielded significantly higher LH levels and ovulation success compared to control. The only difference in LH levels was a higher level with 10 μg kg− 1 at 24 h post-treatment. No differences were observed in ovulation success (≥ 60% of females) among mGnRHa treatments. However, non-linear regression analyses indicated increasing LH concentration and ovulation rate with increasing mGnRHa dosage. This trend implies that dosages in the range of 10–20 μg kg− 1 of mGnRHa can be considered reliable and effective concentrations.