A. Barbaro, A. Francescon, G. Bozzato, A. Merlin, P. Belvedere, L. Colombo-1997
Aquaculture, 154: 349-359
Abstract:
Ovulation and spawning were induced in gilthead seabream, Sparus aurata L., which had failed to spawn spontaneously after thermal manipulation, using a long-acting commercial preparation of leuprolide acetate, an agonist of gonadotropin releasing hormone (GnRHa), in order to study the effects of this treatment on spawning periodicity, the timing of spawning, daily egg production and embryonic viability. Grouped and single females bearing yolky follicles were implanted once with 20, 40 or 80 micro g/kg (body weight) of GnRHa encapsulated in biodegradable copolymer, copoly(DL-lactic/glycolic acid ratio of 3:1). All treated females started to spawn after 48 h and about 40% of the eggs were laid during the initial 10-day period with daily peaks of 10^5 eggs/kg. The mean daily production of viable eggs ranged between 71-288 x 10^2 eggs/kg. Embryonic viability was equivalent to that of control fish which were induced to spawn with a rise in water temperature. There was, however, a significantly (P<0.01) higher egg production in the GnRHa-treated fish. While egg laying occurred regularly at dawn in controls, the long-acting GnRHa tended to shorten the normal 24-h ovulatory cycle of seabream, gradually shifting spawning from dawn to sunset. In tanks with single females, sudden spawning readjustments were observed from sunset to dawn through short 12-h ovulatory cycles. Interestingly, spawning of single females with two males resulted in a greater percentage of non-fertilized eggs in comparison to group of spawning females maintained with a similar ratio of males, presumably as a result of territorial competition when few males try to occupy the same spawning tank.
(Instituto di Biologia del Mare, CNR, Castello 1364 / A, 30 122 Venezia, Italy)