WGD commonly leads to the functional specialization of paralogous genes, or gene co-option, and contributes to vertebrate morphological innovations. Recently, khdrbs1a and khdrbs1b were found both mainly expressed in the brain primordium of zebrafish embryos, hinting at the clue that khdrbs genes may play critical roles in vertebrate brain development. We thus hypothesized that investigating the gene expression patterns of the four zebrafish khdrbs genes might illuminate the origin of the vertebrate brain during evolution.