本邦南岸域における浮游性幼稚魚の生態

Abstract

More than 400 towings of surface and sub-surface layers were carried out to obtain informations on the distributional features of larval fish in the waters off central Japan. The results obtained are as follows: (1) More than 72000 individuals of larval fish were collected. Abundance in both number of species and individuals was high during spring to summer and most of these samples were represented by Engraulis japonica, Scomber japonicus, Trachurus japonicus, Myctophum asperum, Thunnus thynnus and Sebastes inermis, given in the order of abundance. (2) Larval forms are classified into the following three types from their vertical distributions; (i) species appearing only at surface layers, (ii) species appearing at layers far below the surface and (iii) species appearing from surface to the depth of some several ten meters. There is an inverse correlation between the depth of distribution of larvae and the degree of development of chromatophores. (3) Larvae of the dominent species are distributed at layers from surface to sub-surface layers and their zones of distribution move up with their growth. The remarkable diurnal changes of distribution of Engraulis japonica at surface layers are caused by vertical migration of larger sized larvae.