"A long standing question in the reproductive physiology of fish is how the metabolic status determines the onset of sexual reproduction, which often coincides with the start of reproductive migration. We hypothesize that swimming in that case triggers metabolic and hormonal changes critical for the induction of maturation. Studies on migrant fish like eel and salmon support the hypothesis that swimming triggers sexual reproduction, mobilises energy reserves for fuel and positively influences gamete quality. The mechanism behind this is however non-elucidated. Exercise, such as performed by migratory species, can be used as an experimental factor in studying the interaction between the metabolic processes and the onset of sexual maturation. This knowledge is important in optimising aquaculture of commercially interesting species, taking rainbow trout as a model. This study will identify the key metabolic and hormonal factors and their expression profiles in the onset of sexual reproduction as induced by swimming. Using microarray technology, the transcriptional response to exercise of all important tissues involved - gonad, muscle, liver, fat, brain and pituitary - will be analysed in a holistic approach. The main genes involved in both reproductive and metabolic functions will be identified. The role of insulin-like growth factors, the most important candidates, will be established. The expression profile of the main identified genes will be confirmed by real time PCR. The function of the main regulated genes will be investigated in vivo by implanting zebrafish cells that express each of the selected genes. The career objective of the applicant is to acquire additional skills and expertise in becoming a multidisciplinary fish reproduction expert. In addition he would have insight in the role of swimming as natural reproductive trigger. The host and collaborators have an excellent scientific status and are capable to support this project."