Unusual brain nucleus in the diencephalon of a perciform (nototheniid) fish from Antarctica

This cytoarchitectonic analysis on the rostral diencephalon of antarctic perciform fishes confirms the previously established perciform diencephalic body plan. However, it resulted in the detection of an additional, large and conspicuous brain nucleus (unusual nucleus, UN) in the antarctic nototheniid Pleuragramma antarcticum. This nucleus has not been seen before in any other perciform. The UN is probably homologous to a visually related nucleus (named nucleus rostrolateralis and lateral entopeduncular nuclear area, respectively), that has so far only been found in two most primitive (osteoglosso-form) and one most highly derived (atherinoform) species of teleost. Our present results indicate that this brain region, which belongs to the ancient diencephalic organization of ray-finned fishes, is expressed in the brains of fishes due to their particular requirements regarding life styles rather than due to their phylogenetical relationships.