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The gut contents of 575 larvae of jack mackerel Trachurus japonicus collected both day and night in seven depth layers (0–10, 10–20, 20–30, 30–40, 40–50, 50–70, and 70–100 m) using a 3 m2 mouth area frame net at Sta. V (27° 50′N, 126° 00′E) on 26–27 February 2003 in the Kuroshio frontal area of the southern East China Sea were examined. Copepods formed 99.0 % of larval gut contents, and larvae less than 5 mm body length (BL) in the 0–10 m layer fed mainly on copepod nauplii and copepod eggs while they hardly fed on highly mobile copepod copepodites which were the same size as eggs. Gut contents of larvae less than 5 mm BL showed differences between the 0–10 m layer and the 10–20 m layer, with potential reasons for such differences relating to visual acuity. Larvae of 5 mm BL or more fed mainly on copepod copepodites and copepod eggs at 0–30 m depth and mainly on copepod copepodites at depth greater than 30 m.

Larvae of jack mackerel Trachurus japonicus were sampled in seven depth layers (0–10 m, 10–20 m, 20–30 m, 30–40 m, 40–50 m, 50–70 m, and 70–100 m), with a closing-type frame net, on 26th–27th February, 2003, at Sta. V (27°50′N, 126°00′E) continental shelf edge in the southern part of East China Sea, to examine their vertical distribution. Most of the larvae (>90%) occurred in the upper 50 m layer during both day and night. In the daytime, larvae of length from 3.0 mm to 4.5 mm were most abundant in the 10–20 m layer, those from 5.0 to 6.0 mm were most abundant in the 20–30 m layer, those from 6.0 to 8.0 mm occurred at greater depth, in the 30–40 m layer, and those more than 9.0 mm were found in the 0–10 m layer and performed ontogenetic vertical migrations. Larvae from 6 mm to 8 mm length performed diurnal vertical migration, for the percentage (16.7%) of larval number in the 0–20 m layer in the daytime increased to 42.1% at night and the percentage (78.1%) in the 20–50 m layer in the daytime decreased to 49.0% at night.

Growth and ontogenetic migration of greeneye Chlorophthalmus albatrossis were studied in the area from 100–400 m depths in Tosa Bay, from April 1996 to March 1997, using samples collected by an otter trawl net with a 1.3 mm mesh cod end. In the monthly changes of the standard length (SL) composition, four year classes were recognized, although the third- and fourth-year classes were not clearly separated in all the monthly samples. Individuals of 40–50 mm SL settled on the bottom of the 150–200 m depth zone from August to February. By May and June, they grew to 75–80 mm SL modal size, and migrated to 200–300 m depth. In one year after settlement, they grew to 125–130 mm SL, and migrated to 300–350 m depth. They grew to a maximum of 160 mm SL and were not sampled in the winter three years after settlement, suggesting either migration or mortality. Seasonal changes in the gonadosomatic index for combined samples of males and females showed that greeneye did not mature in Tosa Bay. It is suggested that the planktonic larvae are transported from the spawning grounds, the location of which remains unknown.

We examined the stomach and anterior intestine contents of 123 juvenile Trachurus japonicus over a range of body lengths from 10.7 mm to 51.6 mm, which were sampled in the area south-east of Kyushu on 21 April 2000 using a frame net. Numerically, 97.8% of the prey were copepods. Juveniles of a body length class from 10 mm to 12.5 mm most frequently fed on prey with a body width from 150 µm to 200 µm. Juveniles from 12.5 mm to 45 mm and from 45 to 50 mm most frequently ate zooplankton with a body width of 250–350 µm and 350–400 µm, respectively. Generally, the body width of prey increased with the growth of juveniles. We compared the body width frequency of zooplankton collected with plankton nets with that of the prey in the alimentary canals of T. japonicus. Juveniles of body length from 10 mm to 35 mm and more than 35 mm were found to selectively feed on zooplankton with a body width from 250 µm to 350 µm and from 500 µm to 1000 µm, respectively. We conclude that the ability to feed on large prey items is related to the increased behavioral development with growth.