The distribution pattern and the feeding habits of Coilia nasus Temminck et Schlegel were examined in the lower reaches and near mouth of the Chikugo River which is flowing into the innermost of the Ariake Sound. Samplings were made by towing surface and middle layers with some larval nets and also by setting Shige-ami, a kind of set net, at the inflow of the tide in May-December, 1985. At the same time of these fish samplings, measurements of salinity and turbidity, and collections of zooplankton with the net, were also conducted. Feeding habits were analyzed on the basis of the species compositions of the stomach contents and the zooplankton in waters. The results obtained are as follows: 1) The hatching of the eggs seems to take place before reaching to 7-10 km upper area from the river mouth after the eggs are floated down the river for a distance from the spawning ground. 2) The area of 7-10 km upper from the river mouth where the freshwater rushes itself into the seawater is composed of a high turbidity and low salinity waters at the surface and middle layers. 3) The larvae of Coilia nasus are collected most in number in this high turbidity waters and its upstream side. More developed juveniles appear at the freshwater of more upstream region. When the young fishes grow more than about 110 mm in TL, they descend to the estuary of the Ariake Sound. 4) The food composition of the stomach contents in June when the fishes of the prelarval stage come to appear in the river is made up mainly of Cladocera which inhabits in minor percentage in water, but changes gradually to copepod with growth and the almost all stomach of this fish is occupied by copepod even in estuary. 5) The changes in the length of food organisms correspond to growth in the length of the upper jaw of this species. 6) Coilia nasus in adult as well as in larval stage eats small organisms which are not exceeding about 8.0 mm in body length. This species seems to be a plankton feeder throughout life.
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