| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1996: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1995: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
Maturation, Spawning, Development of Egg, Rearing to young fish stage from egg, growth were investigated for Engraulid fish, Coilia nasus, Salangids, Neosalanx reganius and Salanx ariakensis in mainly tidal area of Chikugo River and Ariake Sound. There species distibute in only Ariake Sound and some rivers in Japan. Especially Coilia nasus and Neosalanx reganius are the endemic species in this water. This study was clarified that the spawning time of this Coilia grows late from about sunset in May to about 3 p.m.in August of spawning season and the spawning frequency of this species is only a single during the season according to egg diameter component and histological observation of the gonad. Relation between the day after the hatching (X) and the number of ring on the otolith (Y) is shown by Y=0.9782X+1.0389 and ones from the day age (X) and the body length in mm (Y) Y=0.6857X+2.2976 under the rearing, Y=0.7817X+0.2277 under the wild, respectively. The spawning area of the Coilia is
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10-24km upper reach from the river mouth of Chikugo and this area is tidal area without the salinity. Neosalanx spawns adheshive eggs among coarse sands in almost same area as Coilia's. Relation between the hatch out hour (Y) and water temperature is shown by Y=1.05x10^5/X^<2.18>, as the water temperature of spawning season, from middle of March to early of June, alters 13-24ﾟC,the hatch out hour changes from 16days to 4days. Generaly Salangid doesn't ossify sufficiently in comparison with other Teleostei and this species especially is few in intramembranous ossification, such as the fontanel opens broadly and the unossified adjacent bone during its life. Relation between the day after the hatching (X) and the number of ring on the otolith (Y) is shown by Y=0.99X+0.92 and the ring is formed one before the hatch out, thereafter one per day. The Growth is shown by Total length in mm=0.38x Days after hatch+4.48. It grows about 0.4mm per day, attains the juvenile stage after 36days, to 35mm TL on October, maturates in 38-68mm TL and dyes after several spawns in a year life. The spawning area of Salanx ariakensis locates in 5-25km distance upper reach from Chikugo river mouth and this species spawns also among the sands-gravels and in low Ig loss, high equality and curvature coefficients, and 50% value of sediment. Less
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