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 b 0.05) than was observed
with stimulation bymGnRHa alone orwith metoclopramide alone.Monitoring of LH levels demonstrated a rapid
surge in LH release with the combined treatment versus gradual increase with mGnRHa alone (P b 0.05). Experimental
treatmentswith GnRHa alone, metoclopramide alone and metoclopramide combinedwithmGnRHa 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 b 0.05). No significant differences among groups
(P b 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 b 0.05) were observed in T and 11-KT secretion, with the exception of a significant difference in T secretion
(P b 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.