A very good piece of work, I assure you, and a merry. -Now, good Peter Quince, call forth your actors by the scroll. -Masters, spread yourselves. A Midsummer Night’s Dream. Act 1, Sc. 2 This volume is the outcome of a NATO Advanced Study Institute held in August 1979 at Bishop’s University, Lennoxville, Quebec, Canada. About 130 participants from all the countries of the aJiiance as well as India and Japan attended this event which lasted two weeks. Seventeen of these participants had been invited to present reviews of chosen topics, usually in their specialty. This book is constituted mainly of these presentations, which were prepared as chapters. In addition, six of the participants, whose seminars were found to complement the main chapters, were coopted by the invited lectures/authors to provide additional chapters. Although a lecture was given on electric fields, a chapter on this matter is unfortunately absent due to the lack of preparation time. One may say that Environmental Physiology of Fishes as a discipline originated in Canada. Having been involved as a teacher and worker in this field since 19 54, it was but natural that I was tempted to organise an ASI and get a volume out on the matter. I was encouraged by discussions with colleagues and the acceptance on the part of a large number of eminent colleagues to attend the ASI, deliver lectures and write chapters.