Synopsis This publication is a collection of 22 research papers and review articles on selected topics written by leading experts in the field of fish biology. The write-ups present an overview of the subject and reflect the current trends of fish research at the global level. Some of the research articles offer new interpretations while others bring out the need for a fresh look into the subject. Efforts have been made to gather information on a remarkably wide range of biological adaptations to diverse habitats and ways of life among fishes and to put them in a cladistic framework.