Ichthyology has traditionally emphasized the systematics, anatomy, and distribution of fishes. In the past, most prominent names associated with the field made their major contributions in these areas. Today, however, people who study fish have more far-reaching interests. They study fish to find ways to improve fisheries or aquaculture, to determine the effects of human activities on aquatic environments, and to test ideas in rapidly developing fields, such as ecology, physiology, behavior, and evolution. Growing numbers of sophisticated amateur ichthyologists desire to increase their understanding of fish they keep in aquaria or of those they pursue with hook and line. Regardless of why fish are studied, those studying them still need the basic vocabulary and understanding of fish biology that traditional areas of emphasis provide and that are found in this book, integrated with recent developments in other areas. Our goal is to provide some feeling for the excitement engendered by recent research on fishes. We also want to promote a sense of urgency for the need to protect fishes and aquatic ecosystems. It is critical that a high diversity of fishes continue to be around to fascinate future generations. In large part, this book is designed to serve as a text in classes on fish biology. The large number of chapters and the cross-references within chapters provide instructors of such courses with flexibility when assigning readings in the text. The students we had in mind while writing were junior- and senior-level university students. Our goal, however, is also to provide a useful and palatable summary of recent developments in ichthyology for individuals who have been away from the college classroom for some time and for anyone else who wants an introduction to the most numerous, diverse, and fascinating of all vertebrate groups. This book would not have been possible without the encouragement and help of many people. Initial stimulation and support in fish biology was provided by John B. Moyle, Evelyn W. Moyle, and James C. Underhill (to PB.M.) and by Donald E. Wohlschlag (to J.J.C.). Gary D. Grossman, Donald M. Baltz, and Robert A. Daniels were especially helpful in developing the first versions of many chapters. Numerous graduate and undergraduate students contributed valuable comments on various chapters and/or helped to keep our research programs going while we devoted time to writing. We benefited from discussions with Jeff Graham, Fred White, Tony Farrell, Alan Heath, Carl Schreck, Monica Choi, Stephanie Chun, Hiram Li, Ken Gobalet, Dave Randall, Mikko Nikinmaa, George V Lauder, Laurie Sanderson, Chris Myrick, Cincin Young, Tina Swanson, Carlos Crocker, Shana Katzman, Ann Houck, Ryan Mayfield, Marianne Brick, Keith Marine, Michael Karogosian, Peter Wainwright, and Serge Doroshov. The expert editorial assistance of Chris Myrick and Julie Roessig was especially appreciated during preparation of the fourth and fifth editions, respectively. Ms. Roessig also contributed several original figures to the fifth edition. Trilia Chen also contributed an original figure and editorial assistance to the fifth edition. The reviews of selected chapters in previous editions by Eugene Balon, Michael Bell, David Ehrenfeld, Dale Lott, John Radovich, Arnold Sillman, Randolph Smith, and Paul Webb are appreciated, as are comments by Brooks Burr, Barbara Block, Alfred Ebeling, Kurt Fausch, Malcolm Gordon, Bruce Herbold, Mark Hixon, Paul James, Douglas Markle, John McEachran, Lawrence Page, Theodore Pietsch, Howard Reisman, Frank J. Schwartz, Jerry J. Smith, Timothy Tricas, Linda A. Ward, and Ronald M. Yoshiyama. Theodore Pietsch, Joseph Eastman, Leonard J. Compagno, and Tim M. Berra kindly shared with us their photographs and illustrations of curious fishes. Marjorie Kirkman-Iverson and the staff of our department assisted us in many ways--but especially by keeping the departmental office running efficiently, making iJoseph J. Cech Jr. is the author of 'Fishes: An Introduction to Ichthyology (5th Edition)', published 2003 under ISBN 9780131008472 and ISBN 0131008471.