2019 Volume 57 Issue 1-2 Pages 25-42
Occurrence patterns of the larval and juvenile Japanese whiting, Sillago japonica, were investigated in Tokyo Bay by monthly samplings using the following two types of gear: a small seine net towed at three tidal-flat stations around the river mouth of Tama-gawa River from May 2006 to September 2009; and a ring net towed at a station in the offshore water of the Tama-gawa River mouth from January 2006 to May 2008. Their functional development was also observed mainly by osteological characters on the basis of 111 cleared and stained specimens of 2.0-21.1 mm in body length（BL）. Specimens collected from the offshore water were 30 in number with 4.6 ± 1.6（mean ± SD）mm BL, ranging from 2.0 to 8.5 mm BL, and those from the tidal flats were 232 with 15.7 ± 5.6 mm BL from 6.1 to 49.3 mm BL. Based on the functional development of swimming- and feeding-related characters, the larvae and juveniles were divided into five and four developmental phases, respectively. Improvements of swimming and feeding functions observed at about 3 mm BL were considered to assist the early larvae in migrating shoreward, and the specimens of 6.0-8.9 mm size classes occurred in both the offshore and tidal flat stations. Thereafter on tidal flats, the number of individuals increased and reached a peak at about 15 mm BL, when the juveniles acquired functional swimming and feeding abilities. The juveniles > 15 mm BL decreased in number, and then those ca. 30 mm BL had scarcely appeared on the tidal flats. The Japanese whiting juveniles > ca. 30 mm BL in the innermost Tokyo Bay are most likely to move into deeper waters.
