Sustained administration of GnRHa increases milt volume without altering sperm counts in the sea bass

Abstract

The role of gonadotropin‐releasing hormone (GnRH) in spermiogenesis and spermiation is not well understood. This study examined the effects of different modes of administration of a GnRH analog (GnRHa; [D‐Ala6,Pro9NEt]‐mGnRH) on spermiation in the sea bass, Dicentrarchus labrax. Groups of sea bass received either GnRHa injection in saline (I; 25 μg/kg body weight [BW] or one of three types of GnRHa sustained release polymeric device: a fast‐releasing implant (ethylene‐vinyl acetate copolymer [EVAc]; 100 μg/kg BW), a slower‐releasing implant (ethylene‐vinyl acetate copolymer [EVSL]; 100 μg/kg BW), or biodegradable microspheres (M; 50 μg/kg BW). Total expressible milt was collected and assessed for volume, motility, and counts at various intervals for 44 days. Untreated males produced a total of 9.4 ± 3.4 ml/kg BW (mean ± SEM) of milt over the 44‐day experimental period, with milt production ending by day 28. All GnRHa treatments stimulated a significant increase in total milt volume (ml/kg BW) peaking by day 2 (I: 11.8 ± 1.8) or day 7 (EVAc: 20.0 ± 1.5; M: 26.8 ± 2.7; EVSL: 27.9 ± 4.3) posttreatment. While milt volumes in injected males returned to control values by day 14, all groups treated with sustained GnRHa delivery systems maintained significantly elevated milt volumes for 21 days (EVAc group) or 35 days (EVSL and M groups). Sperm motility was consistently good to excellent (70–100% vigorously active) in all groups when expressible milt volume was above 1.0 ml, and there were no significant differences in sperm counts (averaging 5.5 ± 0.1 × 109 spermatozoa/ml). These data show that sustained administration of GnRHa significantly increases and prolongs spermiation in the sea bass without altering sperm concentration or quality. © 1996 Wiley‐Liss, Inc.

Effects of re-stripping on the seminal characteristics of pacu ( Piaractus mesopotamicus ) during the breeding season

“…These results indicate that this management does not induce depletion, regression or rest in RS1 or RS2 males. Thus, it is possible that using GnRHa for hormonal induction may have influenced positively the milt quality in re-stripped pacu, as has been reported for D. labrax treated with GnRHa, which exhibited increased and prolonged spermiation (Sorbera et al, 1996). Hormonal stimulation of spermiation and re-stripping of pacu need to be explored in future studies.…”

Luteinizing Hormone Plasmid Therapy Results in Long-Lasting High Circulating Lh and Increased Sperm Production in European Sea Bass (Dicentrarchus labrax)1

“…Sperm samples were collected 2 days before the first injection and weekly until Day 34. This period largely covers the time of response to spermiation induction already reported in sea bass [37,38]. Before sperm collection, the genital area was cleaned with fresh water and thoroughly dried.…”

“…In addition, the total milt collected was more than double in treated fish, both scLh protein and plasmid, than in control fish. This is in the range of the milt production obtained with different GnRHa-releasing devices in sea bass [37]. It is remarkable that the increase in sperm release did not alter its quality, in terms of density, showing levels similar to those obtained by Sorbera et al [37].…”

“…This is in the range of the milt production obtained with different GnRHa-releasing devices in sea bass [37]. It is remarkable that the increase in sperm release did not alter its quality, in terms of density, showing levels similar to those obtained by Sorbera et al [37]. This is an important issue to consider for a maturation-inducing method, and because the methodology used in the present work is more direct in its action than the use of GnRHa, we consider that our approach could be suitable to induce gonad maturation and spawning.…”

Changes in Plasma Gonadotropin II and Sex Steroid Hormones, and Sperm Production of Striped Bass after Treatment with Controlled-Release Gonadotropin-Releasing Hormone Agonist-Delivery Systems1

“…The apparent absence in most fish of a down-regulation of GTH II release in response to sustained GnRHa stimulation [19] has led to the development of sustained-release GnRHa-delivery systems for the induction of gonadal development and maturation [12,20,21]. The effectiveness of sustained GnRHa treatment in enhancing spermiation has been the focus of recent investigations [21,22], but except in Atlantic salmon (Salmo salar) [17], the long-term effects of GnRHa-delivery systems on the plasma profiles of important reproductive hormones have been examined only in females.…”