環境・性別及び鱗層に依る鮎の形態的特徴の差異竝びに天然鮎と養殖鮎の識別に就て

抄録

With the liberation of fry and propagation of Ayu, deciding morphological characteristics between Natural Ayu and Pond-cultured Ayu is attached great importance to estimate the commercial value and establish the protection and conservation of Ayu. And the difference of growth degree in living place form an interesting data for our study.
The measuring position is illustrated in Fig. 1. The measurement value is respectively compared with the ratio to the body length, and showing the following formula to 1w (average value of distance between each growth ring), I (scale length-distance from the nucleus to the edge of apical' field) and L (body length), scale's circuli are compared with everybody:
1W/1×L×100=K
These results will be summarised as follows:
(I) The sexual dimorphism (The measuring result is illustrated in Table 2 & 3).
a) Male's body breadth is wider. Female's shape is asymmetric in maturity.
b) Male's Dorsal, Anal and Pectral fins are longer., There is no dissimilarity between male's Caudal fin and female's one.
c) Dorsal fin of male is situated forwards, and Anal fin lies backwards.
d) Male's head height is higher, and its length is shorter.
e) Male's fusiform speck situated in the upper part of pectal fin lies forwards.
f) Pearl organ, secondary sexual characteristics, is generally appeared in male, but the coefficient of the apparition in female is only 14.2%
(II) The dimorphism in respect of circumstantial difference (the measuring result is illustrated in Table 4 & 5).
a) Body breadth of pond-cultured Ayu is wider. I conceive this is rather attributable to the animal bait than the water current.
b) Body heirht of female natural Alm is apt to be hirher.
c) Ventral and Anal fins of female pond-cultured Ayu are severally situated forwards.
d) The position of pond-cultured Ayu's Anal fin is higher.
e) Head length of male natural Ayu is longer.
f) The speck of female pond-cultured Ayu lies forwards.
(III) The difference of scale's circuli (illustrated in Fig. 2 & Table 6).
The scale's coefficient of natural Ayu is smaller than the pond-cultured Ayu's. This is due to the propriety of growth, I consider. We can disceiminate the natural from the pond-cultured: If body length is up to 18 cm., K is 50, not exceeding 55 if it is up to 24 cm. And also it is possible that finding K, we can suggest the limnological factors of surroundings where Ayu lives or the skill of pond-culture technique.