Dopamine control of LH release in the tench (Tinca tinca)

Tench (Tinca tinca) is apparently the only known member of the Cyprinidae in which ovulation is stimulated following administration of a low dose of GnRH analogue (GnRHa) without a dopamine inhibitor. This study evaluated LH release effectiveness of the most commonly used GnRHa and clarified whether LH secretion followed by ovulation is subject to inhibitory dopaminergic control in tench. Fish were intraperitoneally injected with three types of GnRHa, GnRHa with dopamine inhibitor metoclopramide (combined treatment), or the dopamine inhibitor metoclopramide alone. LH concentrations at five sampling times (0, 6, 12, 24, and 33 h) together with ovulation success and fecundity index were recorded. The combined treatment triggered an almost immediate LH release peak with a gradual decline, and resulted in a high ovulation rate. In contrast to the combined treatment, an application of GnRHa alone at 10 μg kg−1 induced gradual increase of LH concentrations with peaks close to ovulation time, and with high ovulation success. Significant differences in LH concentrations at 6 and 12 h and no differences in ovulation success were found between the combined and the GnRHa alone treatments. Metoclopramide alone induced a small increase in LH with no ovulation. The study presents clear evidence of dopaminergic control of LH release in tench, with a high ovulation rate obtained after application of GnRHa alone or in combination with dopamine inhibitor.

Plasma levels of LH in females after treatments.Figure optionsDownload as PowerPoint slideHighlights
► GnRHas and GnRHa with metoclopramide were injected to female tench.
► All GnRHas resulted in a gradual increase in LH and ovulation.
► GnRHa and metoclopramide resulted in an immediate LH surge and ovulation.
► Dopaminergic inhibition does exist in the tench.