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Doctoral dissertation on egg development in halibut

This knowledge will make it easier to ensure good egg quality when farmed halibut are stripped. Halibut farming is dependent on the reliable production of viable halibut larvae, which requires knowledge of the fish’s reproductive biology. Since halibut do not voluntarily spawn in captivity, it is necessary to know when the fish are ready to spawn.

By identifying the hormones and receptors that control spawning, the process can be made more predictable so that the eggs can be stripped when they reach their peak of quality. In her dissertation Kobayashi explains how asynchronous egg development is regulated in halibut. She studied two important sex hormones in the pituitary gland and their receptors located on the egg’s surface. The findings showed that the production of the two types of receptors vary throughout the different stages of egg development up to spawning. As a result, the hormones of the pituitary gland stimulate the eggs to varying degrees depending on which receptor is on the egg surface. Consequently, all the eggs eventually become ready for spawning, although the different groups of eggs are in different phases of development. Kobayashi has used molecular techniques to isolate the genes involved and to study when and how these genes are activated in the halibut throughout the spawning season.

Tamae Kobayashi is 32 years old and comes from Aichi, Japan. In 2001 she completed a Master’s of Engineering at Tokyo University of Agriculture and Technology. She first came to AKVAFORSK in Norway on an exchange through the International Association for the Exchange of Students for Technical Experience (IAESTE) and stayed to complete a doctoral degree on halibut. Her dissertation was conducted at the Norwegian University of Life Sciences (UMB) under the supervision of Professor Øivind Andersen (AKVAFORSK/UMB). The dissertation is entitled “Molecular studies of the gonadotropins and their receptors in the multiple spawner Atlantic halibut (Hippoglossus hippoglossus)”. The defence was held on 22 February 2007 at UMB, Norway.