Multiple spawning and egg quality of individual European sea bass (Dicentrarchus labrax) females after repeated injections of GnRHa

Abstract

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.