Spawning induction of individual European sea bass females (Dicentrarchus labrax) using different GnRHa-delivery systems

The present study evaluated the effect of different delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa) on spawning induction, and egg and larval quality in female European sea bass (Dicentrarchus labr ax). Mature females (mean +/- S.E.M. oocyte diameter = 905 +/- 10 mum) were treated with [D-Ala(6), Pro(9) NEt]-mGnRHa using GnRHa-loaded microspheres , Mc (60 mug kg(-1) body weight, bw) GnRHa-loaded implants, EVAc (50 mug kg (-1) bw) or received a single injection of GnRHa in saline, IN (15 mug kg(- 1) bw). Controls (C) were injected with saline. Females were allocated indi vidually in 2-m(3) tanks with two GnRHa-treated males and were allowed to s pawn without further handling. All GnRHa treatments induced spawning 3 days after treatment (d.a.t.), whereas control fish did not spawn during the 21 -day experimental period. GnRHa microspheres and implants induced up to fou r consecutive spawns in one female, whereas GnRHa-injected fish spawned onl y once. Egg quality seemed relatively lower in all GnRHa-treated Groups com pared to spontaneously spawning fish (natural spawns, NAT Group) maintained in large populations (80 fish in 15-m(3) tanks), possibly due to both the isolation of individual females in separate tanks and the stress from handl ing. Mean egg quality of the first spawns was variable, but similar in all GnRHa treatments (6.6-18.2% buoyancy; 21.7-27.4% hatching). In subsequent s pawns, the Me-treated females produced eggs of higher buoyancy than the EVA c group (20.5 +/- 6.0% vs. 2.87 +/- 1.14%), and similar to the first spawn of the GnRHa-injected group. Our results indicate that, compared to a singl e GnRHa injection, GnRHa-loaded microspheres can induce multiple spawns in European sea bass, without a negative effect on egg quality. (C) 2001 Elsev ier Science B.V. All rights reserved.