Literature concerned with the appearance of smolts (silvery color, streamlined body form), their physiology (salinity relationships, endocrinology), and their behavior (territorial and schooling) is discussed in relation to key steps that may have been taken in the evolution of the parr–smolt transformation and seagoing behavior. In this discussion, it is assumed that Salmonidae evolved in fresh water, that the genus Oncorhynchus originated in a large area of brackish water such as the Sea of Japan, and that schooling oncorhynchids (for example O. gorbuscha and O. keta) are the most specialized of the seagoing salmonids while species of char (Salvelinus) and trout (Salmo) are more primitive.