Reproductive Physiology of Female European Eel

• Main Author: Jørgensen, Michelle Grace Pinto
• Format: Book
• Language: English
• Published: DTU Aqua 2020
• Subjects: European eel
• Online Access: https://orbit.dtu.dk/en/publications/51b2afdb-3d10-4026-9a45-b30cdfcb1c1b; https://backend.orbit.dtu.dk/ws/files/219765552/PhD_Thesis_MichelleJ_rgensen_09062020_edited.pdf

The European eel is known for its complex life cycle and long migration from continental habitats in Europe and North Africa to their spawning area in the Sargasso Sea. Still, significant gaps in knowledge remain on their reproductive development, spawning and early life history. As for all vertebrates, gonadal development in fish is controlled through endocrine regulation on the brain-pituitary-gonad axis triggered by external and internal cues. In eels, a dual neuro-endocrine control on the brain-pituitary axis prevents sexual maturation in continental habitats. In captivity, this inhibition remains and consequently, farmed eels do not reproduce naturally. From a commercial perspective, this impedes closed cycle production and development of a sustainable aquaculture of this species that presently is critically endangered. Nonetheless, gonadal development can be induced through hormonal treatments in captivity. For female eels, this is achieved using treatments with pituitary extracts from carp (CPE) or salmon. The extracts contain the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that stimulate the activity of two key organs, the ovary and liver, which are responsible for ovarian development and vitellogenesis. Furthermore, treatment with a maturation inducing steroid is needed to complete oocyte maturation and ovulation. Current hormonal treatments are suboptimal and the resultant reproduction success and egg quality are exceedingly variable. In this context, the focus of this PhD thesis was on studying characteristics of hormonally induced ovarian development and vitellogenesis in European eel with emphasis on the endocrine regulation in and between the ovary and liver. The thesis includes three interrelated experimental studies. The objective of the first study was to expand insights into the endocrine regulation of induced ovarian development and vitellogenesis with focus on the ovary and liver, as well as subsequent reproductive success. Two commonly used CPE treatment ...