A STUDY ON THE GROWTH OF THE CIRCULUS OF THE SCALE, AND FEATURE OF THE "FRY RING" AND THE FIRST ANNULUS IN GRASS CARP CTENOPHARYNGODON IDELLUS(C. & V.)

The present paper deals with the growth of scales of the subyearlings and yearlings of the grass carp, concentrating on the growth of circuli and features of the "fry ring" and the annuli. The results are as follows:(1) The fry of grass carp begins to grow out scale when it reached a size of about 20mm. According to our observation, the forming of circuli in the scale of the subyearling was quickest during the second month after hatching, by an average of 0.8 circulus per day. Later, the forming process decreased gradually and ceased during winter.(2) The "fry ring" may be observed in most individuals. It is situated at the miter border of the first closely-spaced circuli from the center of the scale. The body lengths of fish at the time of "fry ring" formation ranged 47—70mm.(3) The annulus is marked by a "check", where a group of old circuli of previous year are intersected by two or three new cireuli formed in next spring. This character enables one to distinguish the first annulus from the "fry ring".(4) Circulas indention form during periods of starvation, even the formed circulus around the periphery of scale was resorbed. Thus, the formation of "checks" seems to be related with the rearing conditions.(5) Positive correlations exist between body length and scale radius, between body length and the mean number of circuli on the scale, and between scale radius and number of circuli. Their regression equations are given in the paper.