THE FORMATION OF ANNULI ON THE SCALE OF THE CARP IN LIANG-TZE LAKE

We have attempted age-determination of the Carp(Cyprinus carpio)by investigating the difference in interspaces between circuli from the focus to the periphery of the scale. Our results show that there is no remarkable difference in interspace between circuli which may indicate the formation of the annulus.It is found,however,that there are noticable markings between successive groups of circuli,where the new group of circuli intersects the old group of circuli.These intersections are especially conspicuous at the boundary be- tween the posterior and lateral fields of the scale.These represent,actually,the annulus formation. Annulus formation is usually associated with one or more of the following pheno- mena:1)there may appear a breakage of usually two to three circuli,so that a certain irregular pattern of circuli results;2)a distinct space may appear resulting from the lack of one or two circuli;3)two or three circuli may be more closely arranged,becoming visible as a dark band;4)at the boundary between the posterior and lateral fields the new formation of circuli may appear as radiating towards the posterior margin of the scale. The validity of the above mentioned formation of the annuli in the scales of the carp of Lian-Tze Lake has been established by the analysis of the body-lengths of 560 carp in February 1955.The data of the body-lengths have been plotted against the number of individuals,and the curve thus formed shows two peaks,one around a length of 34 cm. and the other around 45 cm.This finding is exactly in accordance with the scale readings. The season of the annulus formation has also been determined,by the monthly ob- servations on the scales,and it has revealed that the aunuli are formed at the end of summer,immediately after the breeding season.This is confirmed by the observation of the formation of the first annulus on the scales of carp fingerlings reared in ponds.