Scientia Marina, Vol 66, No 3 (2002)

Group-synchronous ovarian development, spawning and spermiation in the European sea bass (Dicentrarchus labrax L.) could be regulated by shifts in gonadal steroidogenesis


https://doi.org/10.3989/scimar.2002.66n3273

Juan F. Asturiano
Instituto de Acuicultura de Torre de la Sal (CSIC) - Grupo de Investigación en Recursos Acuícolas. Departamento de Ciencia Animal. Universidad Politécnica de Valencia, Spain

Lisa A. Sorbera
Instituto de Acuicultura de Torre de la Sal (CSIC), Spain

Jesus Ramos
Instituto de Acuicultura de Torre de la Sal (CSIC), Spain

David E. Kime
Department of Animal and Plant Sciences. University of Sheffield, United Kingdom

Manuel Carrillo
Instituto de Acuicultura de Torre de la Sal (CSIC), Spain

Silvia Zanuy
Instituto de Acuicultura de Torre de la Sal (CSIC), Spain

Abstract


European sea bass (Dicentrarchus labrax L.) is a species with group-synchronous ovarian development. A mechanism is required which enables maturation to occur in the first clutches of oocytes without inducing maturation in subsequent clutches. The present study examined the individual plasma variations of testosterone (T), 17,20?-dihydroxy-4-pregnen-3-one (17,20?P) and 17,20?,21-trihydroxy-4-pregnen-3-one (20?S) in both sexes, estradiol (E2) and vitellogenin (VTG) in females (n=15) and 11-ketotestosterone (11KT) in males (n=21), in an effort to elucidate the hormonal control of the reproductive cycle in this species. A sample of oocytes was obtained at every sampling from each female and the stage of development of the most advanced clutch of oocytes was determined and related to the individual hormone plasma levels. Total expressible milt was collected from males at each sampling during the spawning period and variations in the sperm production were related to hormone plasma levels. Successive elevations of plasma T and E2 levels were observed prior to peaks of progestagens, which resulted from the shift in gonadal steroidogenesis and coincided with the maturation-ovulation of the different clutches of oocytes or with increases in the sperm production. Following each progestagens wave, a new shift in gonadal steroidogenesis, resulting in a new elevation in plasma T and E2, was observed. This hormonal pattern was repeated several times depending on the number of ovulations per female. Results from the present study suggest a mechanism, based on shifts in gonadal steroidogenesis, which may be responsible for regulation of group-synchronous ovarian development, ovulation and spermiation in this species. In addition, evidence is presented which supports a role for both 17,20?P and 20?S as the maturation-inducing steroids (MIS) in male and female European sea bass.

Keywords


Dicentrarchus labrax; reproduction; hormones; maturation-inducing steroid; fish

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