Spawning kinetics and parentage contribution of European sea bass (Dicentrarchus labrax) broodstocks, and influence of GnRHa-induced spawning

Increasing parentage contribution in aquaculture broodstocks is important, in order to take full advantage of the available genetic makeup of the chosen fish, and to avoid inbreeding and loss of allele diversity over subsequent production generations. European sea bass (Dicentrarchus labrax) broodstocks were evaluated over two reproductive seasons to examine spawning kinetics, egg production, and parentage contribution during spontaneous/volitional spawning. In addition, we obtained preliminary results on the potential of a hormonal therapy to synchronize spawning and increase parentage contribution. Spawning lasted between 25 and 66 days in January-March and consisted of 12–21 daily spawns per broodstock, with individual females spawning 1–5 times and males participating in 1–8 spawns during each reproductive season. Daily fecundity was variable during the season, without any trend, and so were all the examined egg/larval quality parameters. Parentage assignment of the produced families indicated that the majority of progeny from a whole season may belong to a very small number of breeders, with four females producing up to 80 % of the analyzed eggs, while a single male may sire up to 57 % of the fertilized eggs. No significant improvement in the overall parentage contribution was obtained with the hormonal treatment, using gonadotropin releasing hormone agonist (GnRHa). Nevertheless, the daily fecundity was higher, and parentage of the eggs from the first spawn after GnRHa treatment was more equally distributed to multiple males/females, compared to any volitional spawns. The study demonstrates the need to further improve parentage contribution in European sea bass aquaculture, through synchronization of maturation and spawning. Although the GnRHa induction experiment was not replicated in the present preliminary study, the results suggest that hormonally-induced synchronization of maturation may have the potential of producing a larger number of progenies from more families, from where to select the next generation of breeders for a breeding program.