Fish are extremely successful vertebrates. Because of a long and divergent history they are now found in almost every conceiv­ able aquatic habitat. This radiation has been accompanied by great diversity in structure, physiology, and behaviour. Despite this variability, fish must solve a number of basic problems that are common to all animals. The most important of these are: (1) to find and ingest appropriate food; (2) to avoid predation; and (3) to reproduce. The main purpose of this book is to describe the variety of behavioural strategies that fish use in coping with these problems. My approach has been to draw together material from both field and laboratory work that is widely scattered in the literature. The major emphasis is on field studies, since my main concern is with adaptive solutions to problems, and I believe these are most likely to be correctly perceived by workers who are familiar with the natural ecological setting of their animals. Of course, many details of behaviour cannot be seen and quantified adequately in the field, and therefore I have not ignored laboratory studies. However, even here I have concen­ trated on work that illustrates the variety of solutions that fish use to solve the three basic problems. Much important work, for instance on causation, development, and learning, is not included.