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Studies on the juvenile Japanese sea bass in the Chikugo estuary of Ariake Bay. Changes in distribution pattern and condition coefficient of the juvenile Japanese sea bass with the Chikugo River ascending.

1982; Springer Science+Business Media; Volume: 48; Issue: 2 Linguagem: Inglês

10.2331/suisan.48.129

1349-998X

Yoshiharu Matsumiya, Takumi Mitani, Masaru Tanaka,

Food Industry and Aquatic Biology

The research on the juvenile Japanese sea bass in the Chikugo River estuary of Ariake Bay is proceeded from 1979. In this paper, we examined the changes in the distribution pattern and the condition coefficient with the ascending progress, mainly using the data obtained in 1980. The researches of seven days in total were executed in mid March, late March and mid April. Surface towing by a larva net with 1.3m in a diameter and environmental observations were performed at seven stations set from the estuary to the river basin. 1) A total of 5314 postlarvae and juveniles were collected by 183 tows. As the researches proceeded, the mode of the distribution moved from higher to lower salinity. 2) The mean of standard length during each research was 14.6, 16.1 and 20.1mm, respectively. The ratio of body depth increases in proportion to the length growth and after 20mm in standard length, the ratio keeps stable. Condition coefficient continues to increase with a gentle curve for a while after 20mm. 3) We could not examine an actual distribution of sea basses only in reference to the salinity in the research area. The concept of distance was introduced to the temporal changes in catch and salinity in 1979. In the year 1979, the continual samplings at each station were performed. 4) In mid March, sea basses were mainly distributed in the sea side of the boundary zone between sea and fresh river waters. In mid April, half the number had already reached the fresh water area. Individuals in the fresh water area had considerably increased the condition coefficient. Changes in body length and condition coefficient under ascending a river were examined. 5) Remarkable change in catch when the tide is turning at high or low tide and more catch during rising than during ebbing tide were observed. It may be said that the sea basses display alternative distribution patterns dependent on tidal levels and tidal hours. Preliminary notes on the ascending mechanism of the sea basses were given.