Ontogenetic changes of feeding habits of larval jack mackerel Trachurus japonicus in the Kuroshio frontal area of the southern East China Sea

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 m(2) mouth area frame net at Sta. V (27A degrees 50'N, 126A degrees 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.