Morphological Changes Associated with Growth and Parr-smolt Transformation in Biwa Salmon Oncorhynchus rhodurus and Amago Salmon Oncorhynchus rhodurus

Abstract

Morphological changes associated with growth and parr-smolt transformation of biwa salmon, reared in pond from underyearling May 1983 to yearling September 1984, were examined by follow-ing relative growth of various body parts, body weight-standard length ratios and changes of condi-tion factor, compared with those of amago salmon reared under the same conditions. Changes of body shapes were observed in association with parr-smolt transformation in biwa salmon; relative growth lines differed between each phase, and also from amago salmon. Parr in amago salmon showed inflections in all the relative growth lines at about 10cm in standard length, and relative growth of body depth and body width changed from negative allometry to isometry or positive allometry. On the other hand, inflection in relative growth line was recognized only in eye dia-meter of biwa salmon smolt. Although similar changes of the body shapes in biwa and amago salmon as in the other salmonids were observed in association with smoltification, such as relative decrease of body depth, body weight and condition facter, degree of these changes was smaller in biwa salmon than in amago salmon, reflecting incomplete smoltification in biwa salmon. Significant differences were recognized in almost all of the relative growth lines between biwa and amago salmon in each phase, most remarkable differences being lower body depth and larger eye diameter in biwa salmon than in amago salmon.