Morphological Variations of the Japanese Jack Mackerel Trachurus japonicus

Abstract

Morphological characteristics of four spawning groups of Japanese jack mackerel Trachurus japonicus, spring and summer spawning groups of the Kuroshio Current System and winter and spring-summer spawning groups of the East China Sea and Tsushima Current System were com-pared.
Although there are differences of the allometric growth among three length ranges, in general the spring and spring-summer spawning groups are larger than the summer and winter spawning groups respectively in head length and upper jaw length, etc. The larger fish of the summer spawning group is larger than the spring spawning group in head length and upper jaw length, etc. and smaller in body depth and pectoral fin length, etc.
Morphological differences seen between spring and summer spawning groups and spring-summer and winter spawning groups were also discussed with the differences between 'kiaji' and 'kuroaji' formerly studied around Wakasa Bay.