On the Fish of the Genus Coilia distributed in Ariake Sound

It has been reported that two species of the genus Coilia (Engraulidae), C. mystus (LINNE) and C. ectenes JORDAN and SEALE are distributed in China, Korea and Japan, and that in Japan, both of the species are distributed only in Ariake Sound which is situated in the west coast of Kyushu and the rivers which find the way to the head of the sound. However, nothing has been clarified about their life history, ecology and fisheries in the sound and the rivers. In the course of the studies on the above lines from 1961 to 1965, 167 specimens, 70-370mm in body length, of the genus were collected from Ariake Sound and the Chikugo River and examined for ditermination of species on the basis of four meristic characters, viz., number of anal fin rays, longitudinal scales, scutes and vertebrae. These characters were used by Yoshida to distinguish the foregoing two species collected in Korea. According to the author\u27s examination, the engraulid fish collected from Ariake Sound belong to only one species of the genus; in comparison of the characters of this fish with those of the two species collected in Korea as reported by Yoshida, the fish in Ariake Sound cannot be identified as C. mystus or as C. ectenes, but seems to be an intermediate form having intermediate characters between the two species. Followings are the discriptions of 10 specimens collected form Ariake Sound and the Chikugo River; Head, 6.3～7.1 in body length; body depth, 5.9～7.2; length of pectoral filaments, 3.0～3.8; length of anal fin base, 1.7～1.8. Snout length, 5.1～6.4 in head length; eye-diameter, 6.1～7.1; postorbital length, 1.4～1.5; interorbital length, 3.0～3.4; length of longest dorsal fin ray, 1.2～1.3. Number of gill-rakers, 17～19 on upper limb and 21～25 on lower one of outer arch. Number of dorsal fin rays, 11～13; anal fin rays, 81～97; number of longitudinal scales, 70～79; scutes, 40～52; number of vertebrae, 71～80. In most of the specimens, the maxillary reaches to the base of pectoral fin. The fish of the genus Coilia distributed in Japan was first reported in 1846 by Temminck and Schlegel. It is C. nasus collected by von Siebold from Nagasaki in the west coast of Kyushu. In 1926, this name was regarded by Jordan and Seale as the synonym of C. mystu of China. However, the adjacent sea of Nagasaki is so oceanic, strongly affected by Tsushima Warm Current, that there must inhabit no fish of the genus which is generally distributed in blackish water. Moreover, it must have been difficult for von Siebold to get the specimens of China in Nagasaki in his days. Accordingly, it seems that the Siebold\u27s specimens were not collected from the adjacent sea of Nagasaki, but from Ariake Sound, which is comparatively near Nagasaki (about 25 km from the City) and is the only area in Japan where the distribution of the fish of the genus Coilia is known. If Siebold\u27s specimens were collected from Ariake Sound, the regard by Jordan and Seale should not be right and the abrogated specific name, C. nasus, should be recovered. But, more examinations are needed to prove this presumption. The fish of the genus Coilia is called "Etsu" by local people. It is distributed in the head region of the sound almost all year around and enter the down stream of the Chikugo River in the spawning season from May to August. It is abundantly caught with gill net and has much commercial importance in the down-stream of the Chikugo River and the waters of the sound near the mouth of the river in the spawning season, but the economic impotance and the commercial catch of this fish are not great in other regions of the sound or in other seasons.有明海にはこれまでに,2種類のエツ属の魚,マエツC. mystusとチョウセンエツC. ectenesが棲息していることが報告されている.1961年より1965年の間に有明海奥部とそこに注いでいる最大の川である筑後川の下流において,167個体のエツ属魚類の標本を集め,吉田が朝鮮半島産の2種類のエツ,マエツとチョウセンエツの同定に用いた4つの形質,臀鰭条数,縦列鱗数,稜鱗数と脊椎骨数について測定を行い,吉田による朝鮮半島産の2種類のエツの研究結果との比較を行った.これによれば,有明海には1種類のみのエツ属の魚が分布していて,これは朝鮮半島産のマエツとチョウセンエツとの中間の形態を持っており,どちらかといえばむしろチョウセンエツに近いと考えられる.1846年にSieboldが長崎で採集し,TemminckとSchlegelが記載したC. nasusは,後にJordanとSealeによってC. mystusの異名同種とされたが,日本近海のエツ類の分布より考えて,C. nasusは有明海産エツであつたという可能性が強い. 有明海産エツの分布域は有明海の奥部とそこに注いでいる河川の下流に限られており,5～8月の産卵期には河川の下流に溯上して産卵を行い,冬期は湾奥部の沖合部分で越冬する.有明海におけるエツの漁獲は主に産卵期に湾奥部の河口附近と筑後川下流において刺網類によって行われる