Atlas of adult Danionella fish telencephalon reveals retention of larval characters

The adult Danionella fish telencephalon, a miniature and transparent teleost fish, retains larval characteristics despite its adult size. This retention of larval traits is due to progenesis, a developmental process involving early sexual maturation and cessation of growth. By employing molecular markers, tract tracing, and quantitative analysis of cellular distribution patterns, researchers have created a comprehensive neuroanatomical atlas of the adult Danionella dracula (Dracula fish) telencephalon.

This atlas reveals the extreme reduction of cellular migration from periventricular zones and reorganization of major pallial divisions in Dracula fish and other Danionella species. The caudal pallium of these adult fish exhibits a compartment-like structure similar to insect glomeruli, characterized by a dense neuropil surrounded by a thin layer of somata.

Intriguingly, similar telencephalon features have been observed in larval zebrafish, supporting the hypothesis of a larval-like telencephalon in adult Danionella. Despite the presence of these larval-like features, most canonical regions of the adult teleost telencephalon are still identifiable. To further explore the potential of this unique telencephalon architecture, the researchers have developed a transgenic GCaMP Dracula fish line, an annotated 3D atlas, and aligned functional imaging data to demonstrate its utility in deciphering the impact of the novel cytoarchitecture on the fish's complex behavioral repertoire.