Spawning performance and plasma levels of GnRHa and sex steroids in cultured female Senegalese sole (Solea senegalensis) treated with different GnRHa-delivery systems

Abstract

The aquaculture of Senegalese sole (Solea senegalensis) is limited by the poor spawning performance of the F1 generation cultured broodstock. The present study compared the efficiency of two sustained-release delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa) and a single GnRHa injection on the stimulation of oocyte maturation (OM), sex steroid hormone secretion and spawning.Analysis with an ELISA showed that the administered GnRHa was no longer detectable in the plasma 3, 7 and 14 d after administration via a single injection, microspheres and an implant, respectively. All GnRHa treatments induced a transient elevation of testosterone (T) and 17β estradiol (E 2 ) plasma levels after 1-3 d. Only three spawns were obtained from controls on days 35, 41 and 42 of the study and ovarian biopsies showed abundant fully vitellogenic oocytes, but little OM. Fish given a GnRHa injection spawned sporadically and fist spawn was 20 days post treatment (dpt). In contrast, both GnRHa implants and microspheres stimulated OM and daily spawning from 4-5 dpt for a period of 28 d. Total fecundity in the broodstock treated with GnRHa-delivery systems was 15-22 times greater than controls and 3-5 times greater than GnRHa-injected fish. Although egg quality appeared to be high, no fertilization was obtained. The results suggest that GnRHa-delivery systems are highly efficient on stimulating OM and spawning in Senegalese sole, presumably through the long-term elevation of pituitary luteinizing hormone release, which in turn stimulated the appropriate changes in ovarian steroidogenesis. However, the effectiveness of the treatment was negated by possible dysfunctions of the male breeders or of the reproductive behavior of the broodstock. ACCEPTED MANUSCRIPT

Comparative effects of human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone agonist (GnRHa) treatments on the stimulation of male Senegalese sole (Solea senegalensis) reproduction

“…In Japanese eel (Anguilla japonica) weekly hCG injections stimulated active courtship behaviour before spermiation (Dou et al, 2007). injections (Agulleiro et al, 2006), slow-release microspheres (Guzmán et al, 2009a) and slow-release EVAc-implants (Agulleiro et al, 2006;Guzmán et al, 2009a) induced egg release, with highest efficiency of the slow-release delivery systems (Guzmán et al, 2009a). Effects on males were less conclusive and showed that GnRHa injections and GnRHa implants, given alone or in combination with 11-ketoandrostenedione, slightly stimulated spermatogenesis and milt production (Agulleiro et al, 2006(Agulleiro et al, , 2007.…”

“…On April 2 nd 2005, when external signs of gonad maturation were clearly evident in the broodstock (Guzmán et al, 2008(Guzmán et al, , 2009a copolymer (EVAc, Elvax; DuPont Chemical CO., DE) as 2-mm diameter x 3-mm cylinders (Zohar et al, 1990). Both injections and implants were applied in the dorsal musculature of the fish.…”

“…Both injections and implants were applied in the dorsal musculature of the fish. The doses of GnRHa were based on previous studies in other fishes, including Senegalese sole Guzmán et al, 2009a). The dosage of hCG was based on previous hCG treatment protocols used in other fishes (Schiavone et al, 2006;Dou et al, 2007).…”

“…This has been correlated with reproductive dysfunctions detected in both male and female cultured breeders, evidenced by diminished sperm production in males and low fecundity in females . Cultured females complete vitellogenesis and show elevated plasma profiles of vitellogenin (VTG) and sex steroids during the reproductive season that correlated well with gonadal growth (Guzmán et al, 2008), but they often fail to complete oocyte maturation and ovulation, and most of postvitellogenic oocytes undergo atresia (García-López et al, 2007;Guzmán et al, 2009a). Cultured males complete spermatogenesis and show well correlated profiles of plasma androgen levels (García-López et al, 2006), but sperm production is reduced compared to wild-caught breeders, which is thought to limit significantly the fertilization success in cultured broodstocks (Cabrita et al, 2006).…”

“…In these studies all spawning obtained from both non-treated and GnRHa-treated fish were unfertilized, indicating that the tested hormonal protocols were not successful to induce fertilized tank spawning. It has been hypothesized that failure of cultured broodstock to produce fertilized spawning is highly related to male reproductive dysfunctions, inhibited breeding behaviour and failed synchronization of gamete release (Guzmán et al, 2009a;Howell et al, 2009). …”