Gonadal maturation and spawning of hatchery-produced immature greater amberjack (Seriola dumerili) following administration of single-chain recombinant greater amberjack gonadotropins
Creators: name: Lancerotto, Stefano
name: Jimenez, I.
name: Fakriadis, Ioannis
name: Sigelaki, I.
name: Papadaki, Maria
name: Mylonas, Constantinos
Publisher: name: Zenodo
Year: 2023

description: Introduction
Reports describing reproductively dysfunctional breeders are recurrent in greater amberjack (Seriola dumerili) held under farming conditions. The resulting discontinuity in the supply of gametes of good quality, highlights the priority of alleviating reproductive dysfunctions and augmenting spawning performance to secure egg production. Two experiment were conducted in order to examine the potential of recombinant single-chain Seriola dumerili gonadotropins (rsdGths) in inducing gametogenesis, in pre-pubertal or adult fish. We report here the efficacy of rsd Follicle stimulating hormone (Fsh) and Luteinizing hormone (Lh) in promoting gonadal recrudescence and enhancing reproductive success of greater amberjack.
Methods
In a first experiment, twenty-month-old hatchery-produced F1 immature male and female greater amberjack were treated with rsdFsh (8 - 12 μg kg-1), and rsdLh (10 - 12 μg kg-1) every 7-days for 12 weeks. In the second
experiment, rsdGths (starting at 6 μg and increasing to 12 μg kg-1 of rsdFSH and rsdLH) were administered weekly for six weeks to enhance maturation in 5-year-old adult hatchery-produced F1 greater amberjack reared in tanks. At the expected spawning season, fish were examined for maturation and gonadotropin-releasing hormone agonist (GnRHa, 50 μg kg-1) was administered to induce spawning. Plasma levels of sex steroids were measured using LC-MS/MS and reproductive performance was evaluated through estimation of relative fecundity, fertilization success, larval survival and of sperm quality parameters.
Results & Discussion
Administration of rsdGths for 12 weeks increased significantly plasma androgen levels in both sexes. All treated males were in spermiation, whereas in Control males the testes were dominated by spermatogonia, with spermatocysts with spermatocytes at various stages representing only a small fraction of the gonadal content. On the contrary, no induction of vitellogenesis was observed in rsdGth-treated females, and ovaries were occupied with oocytes at primary growth. In the second experiment, 5y-old untreated females did not mature and no spawns were obtained. On the other side, all fish treated with rsdGths underwent complete gametogenesis. Ovarian biopsies of treated females indicated a steady increase of oocyte diameter over time, with the most advanced ones exceeding 750 μm at week 6 after treatment, while spawning initiated earlier than expected, at week 4 with four spawns in the month of May. Nine additional spawns were obtained after GnRHa implant administration, and its usage allowed to increase both mean (SD) relative fecundity and total fertilization success from 2,283 ± 508 before GnRHa induction to 5,961 ± 1,568 eggs kg-1 and from 7 to 35 %, respectively. The effect of rsdGTHs in plasma steroid levels and sperm quality in 5-year old fish is still under analysis, however the current results prove that the combined usage of weekly rsdGths and a final administration of GnRHa might be beneficial in promoting gametogenesis, maturation and spawning, and in enhancing the reproductive output in F1 greater amberjack maintained in tanks.