Effects of gonadotropin-releasing hormone analog on milt production enhancement in starry flounder Platichthys stellatus

Abstract

The treatment of exogenous gonadotropin or gonadotropin‐releasing hormone analog (GnRHa) is able to solve some problems that are caused by small milt volume or viscous milt in artificial insemination of flatfish species. However, the mechanism of the action of the exogenous hormones on milt production has not been well understood. Therefore, experiments were carried out to study the effects of GnRHa on the milt production and characteristics of seminal plasma in starry flounder Platichthys stellatus. Males were implanted with GnRHa pellets at three different dosages (50, 100 or 200 μg/kg body weight) during their natural spawning season. Milt volume and sperm production increased in a dose‐dependent manner after GnRHa pellet treatments. Spermatocrit and sperm concentration were significantly lower in GnRHa treated groups than in the control group. The sperm motility index was high from day 4 to day 49 in all experimental groups including the control group, and it declined after day 49 in all groups except the 200 μg treated group in which it remained high until day 85. During the experimental period, osmolality, K+ and total protein tended to be higher in the control group than in the GnRHa treated groups. The results suggested that GnRHa treatment increased the milt volume and sperm production ability in starry flounder. The increase of milt volume was twice as rapid as the increase of sperm production. No significant differences in physicochemical composition of blood plasma and seminal plasma were found according to GnRHa dosages, but there were significant differences between GnRHa treated groups and the control group.

Sperm quality of Brazilian flounder Paralichthys orbignyanus throughout the reproductive season

“…The pH values of Brazilian flounder seminal plasma throughout the reproductive season averaged 6.8, similar to the pH values recorded for the seminal plasma of L. ferruginea (6.8) (Clearwater & Crim 1998), but smaller than those recorded for P. maxima (7.1–7.6), P. stellatus (7.3–8.0) and H. hippoglossus (7.3–7.6) (Dreanno et al 1998; Lim et al 2002; Babiak et al 2006).…”

“…The spermatozoa density for P. orbignyanus ranged from 8.9 to 12.7 × 10 9 cells mL −1 , within the same range reported for other Pleuronectiformes, such as P. maxima , starry flounder Platichthys stellatus (Pallas) and H. hippoglossus (Suquet, Omnes, Nomant & Fauvel 1992; Lim, Han & Chang 2002; Babiak et al 2006). Changes in sperm density throughout the breeding season have been reported for several marine species, including P. maxima and H. hippoglossus , whose spermatozoa concentration increased during the reproductive season (Suquet, Dreanno, Dorange, Normant, Quemener, Gaignon & Billard 1998; Babiak et al 2006).…”

Effect of exogenous hormones on ovulation and gonadal steroid plasma levels in starry flounder, Platichthys stellatus

“…The arrow indicates the timing of the second injection Different superscripts indicate significant differences between treatments (P \ 0.05) (Lim et al 2002;Moon et al 2003;. hCG and GnRHa, administered short or long term via injection or pellet implant, increased the milt volume in previous experiments with starry flounder (Lim et al 2002;Moon et al 2003;. However, the effect of exogenous hormones on starry flounder ovulation is unknown.…”

“…GnRHa and hCG treatment has been tested successfully in starry flounder males and has been shown to be an effective strategy for enhancing milt quantity The superscripts indicate significant differences between treatments at that sampling time (P \ 0.05). The arrow indicates the timing of the second injection Different superscripts indicate significant differences between treatments (P \ 0.05) (Lim et al 2002;Moon et al 2003;. hCG and GnRHa, administered short or long term via injection or pellet implant, increased the milt volume in previous experiments with starry flounder (Lim et al 2002;Moon et al 2003;.…”

“…Thus, it is important to characterize the response to these treatments. Protocol development for brood stock management has included studies of the effects of GnRHa on the stimulation of milt production and spermiation in male starry flounder (Lim et al 2002;Moon et al 2003;. Treatment of male starry flounder with GnRHa increased the milt volume, confirming the role of GtH in stimulating milt volume increase in this species over long periods.…”