Smolt Transformation: Evolution, Behavior, and Physiology

Abstract

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 possible key steps in the evolution of the parr-smolt transformation and seagoing behavior. 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 on corhynchids (e.g. O. gorbuscha and O. keta) are the most specialized of the seagoing salmonids while species of char (Salvelinus) and trout (Salmo) are more primitive.