Induced Spermiation of Rainbow Trout, Oncorhynchus mykiss, Using a GnRH Analogue

In this study, the benefits of using the first Iranian made GnRHa [D-Ala6 des Gly10] mGnRH ethylamide, to induce spermiation in male rainbow trout, Oncorhynchus mykiss, were evaluated. In addition, its effect on acceleration and synchronization, quality and quantity of milt and the plasma Testosterone (T) fluctuations were examined.
For these purposes, 40 non-spermiating male rainbow trouts were injected with a mammalian gonadotropin releasing hormone analog (GnRHa) preparations of 0 (control), 30, 40 and 80 μg/kg B.W. or vehicle (propylen glycole). Spermiation was very synchronous and accelerated in treated groups. Six days after first injection, the cumulative spermiation rates reached respectively 40, 49 and 79% in injected groups (i.e. 30 to 80 μg/kg B.W.) while none of the control fish was spermiated. GnRHa injections advanced spermiation and reduced the average time to spermiation from 16±3.67 days for control group to14.3±2.2, 9.2±0.75 and 6.6±0.29 days for treated groups, respectively (p0.05). Circulating levels of testosterone (T) prior to the GnRHa treatment were relatively low in all groups. Treatment with GnRHa induced significant increase in plasma T after 12 h, increasing it to 43.43±5.82, 38.66±5.63, 39.72±5.07 ng/ml in groups 2 to 4, respectively, which were higher than T levels for control (i.e. 24.58±7.13 ng/ml) P