This book is the first of two volumes that cover the entire fish fauna of the Gulf of Mexico. An introductory section that outlines the Gulf's geographical setting, geological origin, current patterns, tides, sediments, meteorology, ecology, and biological exploration is followed by a key for the forty-four orders of fishes known from the Gulf. Keys and descriptions are provided for families, which are arranged phylogenetically, and for the species, which are arranged alphabetically, described, and distinguished from similar species. All but a few species are illustrated.