An over view on the causes, types and role of hormones in fish migration

In terrestrial and aquatic organisms, migration is a very common phenomenon that occurs both on diel and seasonal bases either for, reproduction, feeding or refuge seeking from predators or adverse climatic conditions. Migration is triggers by various extrinsic factors such as, precipitation, water level, current and discharge, lunar cycle, photoperiod, temperature, dissolved oxygen concentration, turbidity and water color, fish density, hunger and apparition of certain insects. The intrinsic factors such as, thyroxin, prolactin, growth hormone, somatolactin, insulin like growth factor -1(IGF-1), gonadotropin releasing hormone (GnRH), luteinizing hormone, follicle stimulating hormone (FSH), testosterone (T), ll-ketotestosterone (11KT), estradiol-17β (E2) and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) has either a direct or indirect role in triggering fish migration. For fish, migration is very essential for their existence, as a single habitat cannot provide abundant of food and ideal environmental conditions for long times. Man has interrupted fish migration by constructing dams, culverts and weirs that break stream continuity. Water pollution and certain toxicant not only altered the physical and chemical properties of water but also negatively affects the olfactory, lateral line organs, metabolism and swimming performance, leading to delay or migration failure. Migration delay or failure is a key factor for species extinction and reduces the availability of fish for human consumption.