The impact of treatment with mGnRHa, mGnRHa with metoclopramide, and metoclopramide on secretion of luteinizing hormone (LH), testosterone (T) and 11-ketotestosterone (11-KT) and on milt and spermatozoon characteristics was studied in male tench Tinca tinca. Male tench were divided into four groups and treated with following preparations: 0.9% NaCl; mGnRHa (25 μg kg− 1); mGnRHa (25 μg kg− 1) combined with metoclopramide (20 mg kg− 1); and metoclopramide (20 mg kg− 1). Administration of the combined treatment induced an LH surge at 12 h post injection (PI) reaching significantly higher values (P < 0.05) than was observed with stimulation by mGnRHa alone or with metoclopramide alone. Monitoring of LH levels demonstrated a rapid surge in LH release with the combined treatment versus gradual increase with mGnRHa alone (P < 0.05). Experimental treatments with GnRHa alone, metoclopramide alone and metoclopramide combined with mGnRHa significantly increased milt production and relative number of spermatozoa kg− 1 BW at 24 h PI compared to controls, with no differences among experimental groups (P < 0.05). No significant differences among groups (P < 0.05) were found in motility or velocity (VLC, VAP, VSL). The only significant decrease of VLC and VAP was detected after treatment with metoclopramide alone compared to all other groups. Nonsignificant differences (P < 0.05) were observed in T and 11-KT secretion, with the exception of a significant difference in T secretion (P < 0.05) at 24 h PI between the combined group and the metoclopramide treatment and the controls. We conclude that the use of GnRH, combined or not with metoclopramide, are suitable hormonal treatments to control the spermiation in mature tench.