Forebrain atlas of Japanese jack mackerel Trachurus japonicus

We have prepared a forebrain atlas of the Japanese jack mackerel, Trachurus japonicus (Perciformes: Carangidae) to provide basic knowledge on the brain that regulates various physiological conditions and behavior. The Japanese jack mackerel was selected as a model species of Carangidae, since the brain of this species is relatively small for a member of this family and is thus suitable for the production of a brain atlas. The external morphology of the brain is described, and a complete series of transverse sections was prepared and stained by cresyl violet. As observed externally, the optic tectum and cerebellar crest appear to be somewhat hypertrophied in comparison with other brain parts, suggesting the importance of visual and lateral line information for this species. The cerebellar corpus is also relatively large, protruding rostrally on top of the optic tectum. This may be related to the requirement of precise motor control for shoaling behavior. A number of sections were selected, so that all the forebrain nuclei are demonstrated in a series of figures. Brief anatomical descriptions for each structure were also given in the text. As observed in the sections, a major finding in the present study of the Japanese jack mackerel is the presence of as many as seven regions within the lateral part of the dorsal telencephalic area. The lateral part of the dorsal telencephalic area is a presumed visual center, and this feature is also in line with the importance of vision for the Japanese jack mackerel.