Induction of spawning of cultured greater amberjack (Seriola dumerili) using GnRHa implants

The objective of the current study was to examine the possibility of maturing Mediterranean greater amberjack (Seriola dumerili) in culture at two different facilities in Greece and inducing spawning using gonadotropin releasing-hormone agonist (GnRHa) implants. Males in both stocks (n = 8) were in spermiating condition in mid June, though sperm motility was low ranging between 5% and 30%, while motility duration ranged between 2.1 and 2.5 min. Females of the first stock (n = 4) at the same time had ovaries with either primary oocytes or early vitellogenic oocytes at advanced stages of atresia, indicating a failure in oogenesis. On the contrary, the only female of the second stock contained oocytes at all stages of oogenesis, including early final oocyte maturation (FOM; oocyte diameter 650 mum). Implantation with a GnRHa implant induced the first spawn about 36 h later. In the absence of another spawn, a gonadal biopsy was taken 15 days later, indicating the existence of more oocytes at post vitellogenesis and some with almost complete lipid droplet coalescence. A second GnRHa implantation at this time resulted in consecutive egg releases after 36 h, 4 and 5 days, with fertilized eggs only at 36 h and 5 days. The study underlines the existence of important reproductive dysfunctions of greater amberjack in captivity, and demonstrates that GnRHa implants can be used for the induction of multiple spawns of viable eggs. (C) 2004 Elsevier B.V. All rights reserved.