Cybium, International Journal of Ichthyology
Copyright © 2005 Société Française d’Ichtyologie

Christine CHEVALIER, Christine DE CONTO, Vincent GOUBIER, Isabelle HARDY & Jean-Marie EXBRAYAT (1)

(1) Laboratoire de Biologie générale, Université catholique de Lyon et Laboratoire de Reproduction et Développement des Vertébrés EPHE, 25 rue du Plat, 69288 Lyon cedex 2, FRANCE.

Résumé. - L’apron du Rhône, Zingel asper L., est un percidé endémique au bassin du Rhône, actuellement en voie d’extinction. La connaissance des modalités de sa reproduction paraît fondamentale pour une conservation patrimoniale. L’étude présentée ici a porté sur une population de femelles issues de la reproduction artificielle en mars 2000 et élevées en bassins extérieurs. L’examen microscopique des ovaires a permis de décrire cinq stades d’évolution des ovocytes et de leurs follicules, notés de I à V. Des follicules postovulatoires ainsi que des atrésies folliculaires sont également observés. L’évolution des ovocytes et follicules a été suivie pendant les 28 mois suivant la naissance. De jeunes ovocytes sont présents dans tous les prélèvements, laissant penser qu’il s’agit de zones de recrutement. Des follicules atrétiques de divers stades sont observés pour toutes les périodes, à partir de l’âge d’un an. Dans les conditions de l’élevage, la maturité sexuelle est atteinte à l’âge de deux ans. L’ovogenèse se déroule pendant l’hiver et le début du printemps, selon un mode synchrone par groupe.

Abstract. - The development of ovarian follicles of Zingel asper (Percidae).

The endemic Rhodanian Percidae Zingel asper L. lives in the Rhone basin. It was found in all this basin at the beginning of 20^th century, but now its repartition is 17% along the 380 km of this area and it is only represented by a few thousand individuals that are scattered in several isolated populations. Z. asper is the subject of a conservation program, but only a few studies were devoted in the past to its reproduction and development. The material included 38 females that were obtained by artificial fertilization in March 2000, and bred in external basins (Allex, Drôme, France). The females were observed from the juvenile stages to the adult condition. The evolution of oocytes and of their follicles was described in five stages, I to V. Stage I (Ia to Ic) concerned the youngest follicles and oocytes without any characteristic cytoplasmic inclusion. At stage II, oocytes were characterized by the presence of fatty droplets; the follicle cells were flattened. At stage III, some cortical vesicles had appeared in the periphery of the oocytes; follicle cells (granulosa) had increased. At stage IV, small yolk globules were observed in the oocytes, fat globules were fused near the nucleus, and the follicle cells became cuborbital. At stage V, the follicle reached its maximal size, yolk fused globules had invaded almost all the cytoplasm of the oocytes and follicle cells again became flat. Some atretic follicles were also observed. The evolution of oocytes and follicles was observed during 28 months after hatching. Small young oocytes and atretic follicles were observed in each sample. In these captive specimens, sexual maturity was reached after two years. The most advanced follicles (stage V) were observed for the first time in 18 month-old individuals, indicating sexual maturity. Stage V follicles were at their maximal size with a lot of yolk fused globules filling the oocyte cytoplasm. In addition, postovulatory follicles were observed in the ovary in July 2002.

Key words. - Percidae - Zingel asper - Sexual development - Follicle oocytes.