Multiple spawning and egg
quality of individual European sea bass (Dicentrarchus labrax)
females after repeated injections of GnRHA
C.C. Mylonas, I. Sigelaki, P. Divanach, E. Mananős,
M. Carrillo, A. Afonso-Polyviou-2003
Aquaculture, 221(1-4): 605-620
Abstract:
Using multiple injections of gonadotropin-releasing
hormone agonist (GnRHa) (10 µg kg-1 bw) spaced 7–14 days
apart, we investigated the multiple-batch group-synchronous spawning
kinetics of individual European sea bass females (n=6) and examined
batch fecundity and egg quality parameters. Spawning was obtained 3–4 days
after each GnRHa injection. A mean of 2.8 spawns female-1 was
obtained, with a minimum of 2 and maximum of 4. Mean relative fecundity of
the first spawn was 320,211 eggs kg-1 bw and decreased
continuously in subsequent spawns, reaching 52,381 eggs kg-1.
Total mean relative fecundity for all spawns was 637,900 eggs kg-1.
Mean fertilization success did not vary significantly among sequential
spawns and ranged between 67% and 91%. On the contrary, there were
significant differences among the four spawns in embryo survival 1 day after
egg collection, hatching percentage and larval survival 4 days after egg
collection, but there was no consistent trend during the study. Significant
positive correlations existed between 4-day larval survival and hatching
percentage (P=0.0002), and between hatching percentage and embryo
survival 1 day after egg collection (P=0.03), indicating that 1-day
embryo survival can be a potential biomarker for egg quality in commercial
hatcheries. The results of the study demonstrate that European sea bass can
produce up to four sequential spawns of high quality eggs in response to
repeated acute treatments of GnRHa, and suggest that a pulsatile treatment
of GnRHa may be necessary to induce the appropriate cycles of hormone
changes for the recruitment, maturation and ovulation of multiple batches of
viable eggs.
(Institute of Marine Biology of Crete, P.O. Box 2214,
Iraklion, Crete 71003, Greece, e-mail: mylonas@imbc.gr)