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To determine the e¡ect of gonadotropin releasing hormone-analogue (GnRHa) treatment on the milt quality of endangered Caspian brown trout, Salmo trutta caspius, the sperm motility (percentage and duration of motility), sperm production (sperm density, spermatocrit and milt volume) and milt pH were measured for GnRHa-treated (the treatment group) and untreated groups (the control group) during the spawning season. For untreated brooders, the values of the motility per cent, sperm density and spermatocrit decreased continuously during the spawning season while the milt volume, duration of motility and milt pH showed only a signi¢cant decrease at the end of the season. For GnRHa-treated males, these parameters increased 14 days after GnRHa treatment (¢rst milt collection) and then decreased continuously towards the end of the season. In addition, the values of milt and sperm density yielded per treated male were higher than that in the untreated group, although these were not statistically di¡erent. In any case, the total sum of yielded milt from the treatment group over the spawning season was higher than that in the untreated group. In this experiment, signi¢cant positive correlations were found between milt parameters as follows: sperm motility vs. milt pH; sperm density vs. spermatocrit; milt volume vs. spermatocrit; and milt volume vs. sperm density. The results show that the treatment of Caspian brown trout by GnRHa can improve the milt quality in terms of sperm motility and sperm production during a spawning season.

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The sex steroid profile of Caspian brown trout was investigated after gonadotropin-releasing hormone analogue (GnRHa) injection throughout the spawning season, i.e. December and January. The values of testosterone (T), 11-Ketotestosterone (11-KT), progesterone (P), cortisol (C) and 17α, hydroxyprogesterone (OHP) were measured for GnRHa treated (the treatment group) and untreated groups (the control group) during the spawning season. In treated males, the values of 11-KT, OHP and C increased 14 days after GnRHa treatment and only showed a significant decrease at the end of the season. Also, the T and P levels showed increases 14 days after GnRHa treatment and then decreased continuously towards the end of the season. In untreated males, sex steroid peaks were observed 27 days after first stripping. In conclusion, our results showed that the GnRHa treatment of Caspian brown trout promotes the final maturation by clear effects on the sex steroid profile.