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Identifier

000448786

Title

Δυναμική της ωοθήκης της σαρδέλας, Sardina pilchardus (Walbaum, 1792)

Alternative Title

Ovarian dynamics of sardine Sardina pilchardus (Walbaum, 1792)

Author

Σέρβου, Ελένη Δ.

Thesis advisor

Σωμαράκης, Στυλιανός

Reviewer

Κουμουνδούρος, Γιώργος
Τσερπές, Γιώργος

Abstract

European sardine Sardina pilchardus (Walbaum 1792) is a commercially important small pelagic species characterized by multiple spawning along a protracted reproductive period in winter. The fecundity of sardine is indeterminate meaning that oocytes are constantly recruited from the primary to the secondary growth phase during the spawning season. The aim of this dissertation was to investigate the pattern of oocyte development and recruitment during the reproductive period of sardine. For this purpose, a suite of methods, techniques and theories in fish reproductive biology (histology, stereology, postovulatory follicle ageing, oocyte packing density theory and oocyte size frequencies distributions) were applied to ovarian samples of fish collected in the North Aegean during November 2018-Octomber 2019. This combination of methodologies allowed for the estimation of the number and size of oocytes at different developmental stages. In a subsequent step, general linear models (GLMs) were used to examine changes in the relative number of oocytes per stage of development in different gonad stages and along the spawning season. In this way, the course of oogenesis between two sequential spawning events was described in detail. The results indicated that during an ovulatory cycle, oocyte numbers remain in a state of dynamic equilibrium. When the advanced batch enters into final maturation, an intense pulse of oocyte recruitment from the primary to the secondary growth phase starts and becomes fully completed two days after spawning. Deposition of yolk occurs continuously both in vitellogenic oocytes as well as de novo but during the final maturation of the advance batch the intensity of vitellogenesis increases. The pattern of oocyte recruitment and vitellogenesis remains unchanged along the course of the spawning season. The number of oocytes in secondary growth and final maturation equals 2-3 times the batch fecundity depending on the gonadal growth phase. Oocyte sizes in different developmental stages differed between gonad stages while the sizes of vitellogenic oocytes changed during the spawning season which seemed to be related to the seasonal changes of water temperature. Finally, in contrast to batch fecundity, oocyte sizes did not relate to fish size.

Language

Greek, English

Subject

Oocyte packing density

Pattern of oocyte development

Stereology

de novo vitellogenesis

de novo λεκιθογένεση

Πρότυπο ανάπτυξης ωοκυττάρων

Πυκνότητα πακεταρίσματος ωοκυττάρων (OPD)

Στερεολογία

Issue date