American eels (Anguilla rostrata) harvested from weirs by the commercial fisheries ofthree Nova Scotian rivers differed in life history characteristics. Depending upon their orientation,weirs captured either downstream-migrating silver American eels or upstream-migrating yellowAmerican eels. Mean lengths and weights of downstream-migrating American eels differedamong rivers, increasing as the run progressed from late August to mid-November. Sexuallymaturing (silver) migrants were larger (typically exceeding 400 mm in length) and older thanimmature nonmigrants and had a higher ovarian gonadosomatic index (proportion of body weightcontributed by ovaries; usually above 1.5%). At a given length, silver eels had larger eyediameterindices (eye width x eye height) than did yellow eels but, for silver eels, eye index wasnot a predictor of gonadosomatic index. Silver eels migrating later in the run were more mature(had higher gonadosomatic indices) than those migrating earlier. Silver eels from different riverswere similar in age and gonadosomatic index. Male silver eels were smaller, less mature, andmigrated earlier than did most females. Skin coloration (yellow-silver) was a fairly reliable guide tosexual maturity (immature-maturing), but histologically detectable maturation may begin one ormore years prior to coloration change and participation in the spawning migration.