Dominika Chojnacka, Paweł Boguszewski, Jarosław Jerzy Barski, Redouan Bshary

As evidence for advanced cognitive abilities in fishes steadily increases, cytoarchitectonic studies of the Actinopterygian telencephalon receive increasing interest by neuro-ethologists. However, the amount of information concerning brain organization in this group is still rather small. Here, we present a cytoarchitectonic analysis of the telencephalon of Labroides dimidiatus, a species showing highly sophisticated interspecific social behavior in cleaning interactions with other reef fish species. Analysing cresyl violet-stained serial transverse sections, we designated cell regions and nuclei on the basis of characteristic size, shape and intensity of pericarion staining, density and distribution of cell bodies, cell-poor zones; congruence of cell groups with brain cellular structure identified in other species, consistent sequence of cell groups in subsequent sections and in corresponding centres of the opposite hemisphere. 27 telencephalic regions and nuclei, 9 in the ventral part and 18 in the dorsal part of the telencephalon were recognized and described.