Salmon broodstock management Endogenous and environmental control of ovarian development and spawning

Available data indicate that the biological process of sexual maturation of Atlantic salmon, as of most temperate fish species, is governed by environmental cues in order to ensure correct timing of the spawning event. Leading up to this event, oogenesis, oocyte and follicle maturation and ovulation are developmental processes that are controlled by the endocrine system to ensure high egg quality at spawning. Thus, environmental cues are likely to influence the endocrine control over the whole period of o varian development. Photoperiod and temperature are key environmental variables in this regard, and can easily be manipulated during broodstock management. In order to establish protocols for environmental control, especially for out-of-season production of high-quality eggs, it is important to establish how photoperiod and temperature interacts with the endocrine control of oocyte growth and maturation. This pertains primarily to the hypothalamic-pituitary-gonadal axis, with the GnRH-FSH/LH system and th e GH-IGF-I system, and the effects of these hormones on oocyte development and steroidogenesis. The research will combine in vivo and in vitro approaches, and will apply molecular, endocrine and morphometric methods. Particular attention will be given to effects of photoperiod and temperature on gene expression of GH, IGF-I, FSH-beta, LH-beta, FSH-R, LH-R, mPR, nPR, GH-R and IGF-I-R, and plasma levels of GH, IGF-I, FSH, LH, T, E2 and 17,20betaP. These data will be related to ovarian development, which wil l be monitored by GSI, by analysis of oocyte size distribution, and by studies on the dynamics of the granulosa cell population. Egg quality will be assessed by measurement of egg size and survival to the eyed stage.