Evolution of fish brains and behaviors: how many ways to generate the same outcomes?

Animals are adapted to their natural habitats. Their brains perceive the world via their sensory systems, compute information together with that of internal states and autonomous activity, and generate behavioral outputs. However, how do these processes evolve across evolution? We discuss the evolution of the brains of teleost fishes, the largest vertebrates group. Although their overall brain organization follows a shared Bauplan and their brain can serve similar functions, significant differences exist between teleost and tetrapod brains at all levels, shape, size, and connectivity. It has become evident that many evolutionary paths can lead to similar anatomical/functional traits independently in different taxa. We here present some examples of teleost sensory organs, afferent sensory pathways, and even some higher-order cognitive functions such as tool-using behaviors that evolved through convergent mechanisms. It appears that the nervous system is highly ‘plastic’ during evolution, and more convergent evolution has taken place than is commonly thought.