Induction of ovulation in
captive-reared dusky grouper, Epinephelus marginatus (Lowe, 1834),
with a sustained-release GnRHa implant
G. Marino, E. Panini, A. Longobardi, A. Mandich, M.G.
Finoia, Y. Zohar, C.C. Mylonas-2003
Aquaculture, 219(4): 841-858
Abstract:
Captive-reared dusky grouper were induced to ovulate
using a sustained-release delivery system (implant) loaded with
gonadotropin-releasing hormone agonist [D-Ala6, Pro9,
NEt]-GnRH (GnRHa). Thirteen females were implanted at doses ranging from
30.5 to 68.3 µg kg-1 during three experiments between late June
and early September. Of the injected females, 85% responded positively to
the GnRHa implant and ovulated between 60 and 238 h after treatment, whereas
none of control fish showed any sign of maturation. No spontaneous spawning
was observed, and the eggs were manually removed from the females using
gentle abdominal pressure. The mean number of ovulations per fish was 3.8,
with a maximum of nine for one female. Overall, a total of 42 ovulations
were obtained, resulting in the production of more than 5 million eggs. The
average relative fecundity was 118.3±16.0×103 eggs kg-1
BW, with a maximum of 202.2×103 eggs kg-1 BW. Mean
percentage fertilisation and hatching were 48.2% and 52.2%, respectively.
The results demonstrate that GnRHa administration via controlled delivery
systems is an effective method for producing good quality eggs in captive
dusky grouper.
(ICRAM Istituto Centrale per la Ricerca Scientifica e
Tecnologica Applicata al Mare, 300 Via Casalotti, 00166, Rome, Italy,
e-mail: g.marino@icram.org)