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Physiological Changes Associated with the Diadromous Migration of Salmonids

The book reviews and discusses present knowledge concerning the diadromous migration of salmonids. It groups elements ranging from ecology to cell biology, to give the reader a background knowledge for critical understanding of published literature and for proper design of experiments. In the first chapter, elements related to the river migration are discussed. These include abiotic and biological factors involved in onset of migration, swimming activity during migration, metabolic aspects, and possible mechanisms for orientation. In the second chapter, structural and physiological changes associated with the transfer between different salinities are described. These include adjustments in water and ion balance, as well as cardiovascular, respiratory, and metabolic changes. In the third chapter, elements of preadaptation to these transfers are reviewed. Comparative aspects between different salmonid species are exposed. The interrelation between smoltification and migration is discussed. The existence of changes in hormone production, metabolism, distribution, and effect during smoltification is underlined. The presence of a preadaptation to freshwater transfer and its putative relation to desmoltification are discussed. An evolutionary hypothesis by which new pathways for inhibition of desmoltification allowed some salmonids to remain in the sea longer is proposed. In the fourth and main chapter of the book, endocrinological aspects are reviewed, with emphasis on thyroid hormones, corticosteroids, and prolactin. For each hormone (group), general knowledge on its synthesis, regulation, metabolism, distribution, and action in fish is reviewed, and its putative involvement in migration, preadatory, and adaptory changes related to salinity transfer is discussed. The diversity and plasticity of salmonids are underlined.