エツCoilia nasus Temminck et Schlegelの生態的研究 : II.卵発生及び仔魚に及ぼす塩分濃度の影響
摘要
The engraulid fish, Coilia nasusTemminck et Schlegel, inhabits only in Ariake Sound which is situated at the west coast of Kyushu in Japan. The effects of the salinity on the embryonic development and hatching of this species were studied to clarify the environmental conditions for the spawning. Eggs were fertilized artificially, and under the conditions of increasing salinity from the fresh to the sea water and the constant salinity, the survival rate and the hatchability of eggs and the survival rate of larvae were examined. They show high values between zero and 11.9‰ in salinity. But, the eggs died and the larvae often take deformity in more than 25.5‰ in salinity. The Chikugo River where this species ascends to spawn has a large mass of fresh water in the area with tidal influence. Its tidal compartment attains to 23 km up the river and the brackish water also extends over so many kilometers in it. The eggs, which are spawned in the upper part of the tidal compartment and transported toward the mouth of river, hatch in the fresh water or low saline water. Among the rivers flowing into Ariake Sound, only the Chikugo River has the environmental conditions, under which the Coilia is able to spawn and eggs to hatch out, such as long tidal compartment and large quantity of fresh water. As a result, it can be said that Colia nasus depends its existence on the Chikugo River.