Overcoming dysfunctional gametogenesis in hatchery-produced greater amberjack, Seriola dumerili using recombinant gonadotropins, and spawning induction using gonadotropin releasing hormone agonist-loaded implants

Abstract

Female greater amberjack, Seriola dumerili reared in tanks have been inconsistent in entering or completing vitellogenesis. As a result, established spawning induction protocols employing gonadotropin-releasing hormone agonist (GnRHa) fail to induce oocyte maturation, ovulation and spawning. Males also exhibit reproductive dysfunctions resulting in low sperm production of relatively low quality. To ameliorate these problems, homologous Seriola dumerili single-chain recombinant Follicle stimulating hormone (sdrFsh) and Luteinizing hormone (sdrLh) were produced and administered to adult 4.8-year-old hatchery-produced (F1 generation) greater amberjack held in tanks, in order to enhance gametogenesis and increase reproductive performance (fecundity and fertilization success) upon spawning induction with GnRHa. Beginning at the onset of gametogenesis (27 April 2022), injections of sdrFsh and sdrLh were given for 6 consecutive weeks (a total of 7 treatments) in different combinations in males and females, and increasing doses. All fish treated with sdrFsh/Lh underwent complete gametogenesis, with females having oocytes in post-vitellogenesis and males producing releasable sperm at the time planned for the GnRHa spawning induction (6 June 2022). Furthermore, five of the six females initiated oocyte maturation prior to the GnRHa treatment, and at least one female also spawned spontaneously earlier (week 4). All but one untreated Control females did not complete vitellogenesis and exhibited follicular apoptosis/atresia, making them ineligible for GnRHa-induced spawning. Untreated Control males completed spermatogenesis and produced releasable sperm, but of somewhat lower spermatozoa density and significantly lower motility percentage and velocity compared to sdrFsh/Lh-treated males. GnRHa-induced spawning of the sdrFsh/Lh-treated fish enhanced mean daily relative fecundity and fertilization success, with embryo and larval survival >50%. These results are encouraging, and we expect that further optimization of dosage and administration timing can provide a reliable protocol for enhancing gametogenesis and promoting maturation in dysfunctional greater amberjack broodstocks maintained in aquaculture indoor facilities.