Freshwater eels are almost infinitely improbable creatures. They spawn and die in the middle of the ocean, often associated with undersea mountains. Their tra- parent, leaf-like larvae move with ocean currents for months or years until they approach the mouths of freshwater rivers. Then they undergo a dramatic transf- mation in morphology, physiology and behavior. They move from their planktonic oceanic environment, migrate upstream and live for several years as apex fre- water predators. Then, almost impossibly, as they become sexually mature, they reverse their migration downstream to the ocean and back to spawning grounds to complete their life cycle. The dramatic changes in their life cycles are incredible. The efforts to unravel the details of their life history have been truly daunting. Much of the past research was the work of dedicated individuals who devoted their lifetime research to these fishes. Freshwater eels merit a separate chapter in almost any textbook dealing with ichthyology, marine biology or animal migration. We know a great deal about some aspects of the biology of freshwater eels. However, our understanding of their bi- ogy still resembles a work of art as much as a work of science. To some it appears like the sweeping brush strokes of a Japanese Zen landscape, to others it resembles the work of a French impressionist, and to still others it appears as magic realism.

This book gathers current data on the two types of fish metamorphoses and their endocrine controls. It will be of interest for fish biologists as well as comparative physiologists and endocrinologists. Metamorphosis is a major developmental phase characterized by morphological and physiological changes. It prepares organisms for a drastic shift in habitat and behavior. Among vertebrates, besides the well-known larval metamorphosis in amphibians, two types of metamorphosis are also described in the life cycle of some fish species. Larval metamorphosis, also called first metamorphosis or true metamorphosis, is encountered in lampreys, representative species of basal vertebrates as well as in some teleost groups, elopomorphs and pleuronectiforms, and possibly also in some other teleost species. Secondary metamorphosis occurs in juveniles of some diadromic migratory teleosts, such as salmons and eels, and compared to larval metamorphosis, involves less drastic morphological changes.

Most of the diadromous fish of the world have decreased in distribution and abundance since the beginning of the twentieth century. They are now threatened, and important conservation issues arise. The causes of these trends vary among species and basins but regional human impact (damming, pollution, fisheries) and global change (climate) are suspected to be responsible for these difficulties. This book contains selected papers from an international symposium organised by the Diadfish network held in Bordeaux (France) in 2005. Readers will find up-to-date information on the ecology, ecotoxicology and physiology of several diadromous species (Atlantic salmon, shads, lampreys, eels) and this whole group in Europe. Main impacts are also documented and analysed in case studies, and solutions or remediation actions are presented.