The last few years have seen a number of new books on evolutionary biology. However most of these are either large or specialized. This is an attempt to produce a thin, general version for undergraduate use. Thinness, of course, demands selectivity, and the aim has been to concentrate on the principles of the subject rather than on the details-principles, that is, of both theory and practice. Thinness also sometimes means that a certain level of knowledge is assumed in the readership, but I hope that this is not the case here, and my intention has certainly been to produce something that is as intelligible to the uninitiated as it is to the well-informed. As for the bibliography, I refer, where possible, to reviews rather than primary sources, so a citation should not be taken to imply any sort of precedence. In developing the theme, I have adopted a loosely historical approach, not only because I believe that this makes for more interesting reading but also because the subject, like the subject it addresses, has evolved under the critical eye of a selective process. Problems have been perceived, hypotheses have been formulated to explain them, facts have been amassed to test the hypotheses, more problems have been perceived, more hypotheses formu lated, and so on.

It is almost thirty years since Professor G. G. Winberg established the basis for experimental studies in fish energetics with the publication of his monograph, Rate of Metabolism and Food Requirements of Fishes. His ultimate aim was to develop a scientific approach to fish culture and management, and the immense volume of literature generated in the ensuing years has been mainly in response to the demand for information from a rapidly expanding, world-wide aquaculture industry and to the shortcomings of contemporary practices in fisheries management. The purpose of this book is not to review this literature compre hensively, but, assuming an informed readership, to focus attention on topics in which new knowledge and theory are beginning to be applied in practice. Most emphasis has been placed on food; feeding; production (growth and reproduction) and energy budgeting, as these have most influence on the development of fish culture. Some chapters offer practical advice for the selection of methods, and warn of pitfalls in previous approaches. In others the influence of new theory on the interpretation of studies in fish energetics is discussed in the context of resource allocation and adaptation. We hope that the scope of material presented here will have sufficient interest and value to help significantly to fulfil Winberg's original objectives.

Ecosystem health offers a fresh perspective on the management of natural resources and the environment. While some of the root concepts can surely be traced back to Aldo Leopold and even earlier, it is only in the recent decade that a substantial body of work has emerged on this topic. There is no question that a novel approach which is by its nature cross disciplinary, bridging the health and biological sciences, will initially raise a number of questions particularly pertaining to the use of metaphors and the validity of the analogy. This volume however goes beyond merely the philosophical dimensions of the subject by covering a number of case studies which have given rise to the development of promising quantitative methods for diagnosis and rehabilitation of ecosystems under stress. The focus of most studies is on regional ecosystems i.e. ecosystems of large scale. As such, the methods and approaches should have wide appeal to government agencies charged with the responsibility of sustainable development of regional ecosystems and natural resources. Health is one of those difficult concepts that everyone thinks they can define, until they come to try. We all have personal knowledge about health and illness and this makes the ecosystem analogy so potentially powerful. Yet it is also clear that the uncritical application of the concept could lead to overly simplistic approaches to analysis and management of ecosystem health."