Morphological studies were made on the scales at latero-central and latero-caudal part of Ayu grown in various environments. These Ayu have spent their larval stage in Lake Biwa, but afterwards it shows different degrees of growth because of difference in environments. The material used in this investigation are all at the same matured age and are consisted of the following three groups; namely, (A) small Ayu living in Lake Biwa only (weighed about 3 gr.) (B) going-up-the- stream in River Ado (weighed about 40 gr.) and (C) transplanted, large Ayu in River Masuda in Gifu Prefecture (weighed about 100 gr.). The results are summarized as follows:
(1) The ratio of the length of scale as well as width among A, B, and C groups was about 1: 3: 4. Almost in all groups, the length of scale measures more than the width in a small extent at latero-central parts, while the width is a little larger than the legth in the measure at the latero-caudal parts. The length-width ratio did not indicate any notable difference among the groups.
(2) In the most cases of B, and C group, the scales at the latero-central parts cover broader than the scales at the latero-caudal parts, while in case of A group, the former was approximately equal to or rather less than the latter, therefore it is apparent that the effect which is severely influenced by the external inhibiting factors for the growth, was not equivalent upon the both scales of A group.
(3) No obv, ous difference is found among these groups of numbers of scales at lateral line and transverse series.
(4) The scales of A group show smooth margin, with few eminent ridges arranged in equivalent intervals and few pseudo-annual rings on the surface. The scales, on the other hand, of B and C group were rather angular in shape with many eminent ridges and often plenty of pseudo-annual rings. The intervals between these eminent ridges are markedly narrow near the focal areaof scale, wider in the neighbouring outer part and somewhat narrow on the peripheral part. These findings are most notable in C group.
It seems that these morphological differences in the scales among these groups are due to the differences in the rate of growth, and in environmental factors.kn-abstract=
