This book represents a brief essay on the ecology of fishes. The book differs in structure from other. Following a short introduction, in which the basic theoretical concepts of modern fish ecology are examined, conclusions are drawn concerning the interrelations between the fish and its organic and inorganic environment. In the second part of the book the fundamental links in the life-histories of fishes are examined. In selecting the examples, author used where possible data concerning species of commercial importance. Primarily, the author examined those aspects of the ecology of fishes which are important for the construction of a rational fishery. Since the ecology of separate species of fishes has been dealt with in detail.