カタクチイワシ

In this report is presented the biological characteristics of the seasonal and the local populations of the Japanese anchovy, Engraulis japonica (Houttuyn), one of the most important commercial fishes in Japan, to analize the different races in the coastal waters. The samples were collected in the waters around Japan including 6 regions along the Pacific coast and 5 regions along the Japan Sea coast (Fig. 1). The morphological characteristics w e re examined on the number of vertebrae, anal and dorsal fin rays, and body proportions. The other characters of the growth and the maturation were studied in relation to the age mark, the types of ridge formation on scale, the spawning season and the fecundity. The results obtained are as follows: 1) In the young, smaller than 50 mm in body length, the average vertebral counts differed significantly by month and region of sampling, being the most reliable among the meristic characters in identifying the different seasonal brood groups (Tabs. 1, 2). The sample groups of the young were characterized by the average number of vertebrae, as V-group with more than 45.30, v-group with less than 45.10. Although in the southern waters V-group dominated in spring and v-group in fall, the appearance of V-group became later and that of v-group became less definable progressively, towards to the northern waters (Figs. 2, 3). The correlation between the average number of vertebrae and the water temperature was generally recognized on the two groups. The remarkable differences did not indicate between V- and v- group in the body proportions and the length-weight relation (Figs. 4-7). 2) The different mark groups were denoted by the scale pattern, as S-group characterized with larger size of the first age mark (S_1) and s-group with smaller size of the first age mark (s_1). The size of Si-mark varied in the different waters, the larger in the northern waters, the smaller in the southern waters, while the size of si-mark was nearly constant in the different waters (Figs. 12, 14, 16, 17). The anterior sector o f scale was characterized by successive two zones, one was wider in the distances between ridges (wide zone) being inner part of scale, the other was narrower (narrow zone). The wide zone occurred between the center and the first age mark of scale, and the size of wide zone (r_0) was closely related with the first mark size (ri). Hence, S- or s-group could be represented by r_0 (S) corresponding to r_1 (S) or r_0 (s) to r_1 (s) (Figs. 22-24). 3) The monthly group maturity was estimated by the frequency of the individuals with ovaries of maturing phase. In the southern waters, the peaks of group maturity were observed in spring and fall. However, towards to the northern waters, the appearance of the spring spawning group became later progressively and the fall spawning group became less significant, and the spawning group occurred in summer in the Hokkaido Region of northern end (Fig. 29). The spring spawner dominated over the fall one in effective spawning amount in the Nankai Region, though both of them were functional spawning group (Tab. 9). 4) The correlations of the biological characters were examined t o obtain the informations of the seasonal and the local populations. The V-group of higher average number of vertebrae was spawned in spring and summer, while v-group of lower average number of vertebrae was spawned in fall. The V-group coincided with S-group with larger size of the first mark on scale, and v-group with s-group (Tab. 10). Adult females of S-group were considered to be the functional spawners in spring and summer, while those of s-group in fall (Tab. 11). 5) Therefore, the seasonal and local populations of the Japanese anchovy are characterized as follows: The seasonal population: The population spawned in spring is indicated by the higher average number of vertebrae, with the larger first mark size on scale and the higher fecundity. The population spawned in fall is indicated by the lower average number of vertebrae, with the smaller first mark size on scale and the lower fecundity. The local population: The spawning season varies in the different waters, and going to the northern waters, the spring spawning season becomes later progressively, while the fall spawning becomes less significant. These local differences correspond to the biological characters by the regions including main spawning grounds. Since the local populations of the Japanese anchovy can be observed by regions during life history of the fish. 6) The anchovy populations are recognized with the average number of vertebrae in the early life-stage, with scale patterns in the developmental stage, and with the maturation characters in the adult fish. The authors esti m ated that these populations are discriminated in terms of the seasonal and the local races, and the Japanese anchovy is defined by two seasonal races of spring and fall spawners, and by the local races of Hokkaido, Tohoku, Tokai, Nankai, Japan Sea, Seikai and Nankai Region, in the main spawning areas.