Brains and Crowds: How Population Density Shapes Brain Size in Wrasse Fish

Fish neuroanatomy is turning out to be far more fascinating than I ever imagined! This is only the second fish-related paper I’ve featured on my blog, and it’s already blowing my mind. The study, "Population density drives concerted increase in whole brain volume in a wrasse species Coris batuensis," explores how population density impacts brain size in the Coris batuensis, a type of wrasse fish. Who knew that the social environment of fish could influence their brain development so profoundly?

What’s So Special About This Study?The researchers found that individuals living in high-density populations had significantly larger brains than those in low-density groups. Interestingly, this increase wasn’t limited to just one part of the brain—it was a concerted enlargement across all five major brain regions, including the telencephalon, hypothalamus, optic tectum, cerebellum, and dorsal medulla.

This suggests that living in crowded environments requires enhanced cognitive abilities to navigate complex social interactions.What’s particularly fascinating is that this brain size variation was linked specifically to intraspecific (within-species) population density. Factors like habitat complexity or the presence of other fish species didn’t seem to play a role. This finding supports a broader version of the “social brain hypothesis,” which posits that social challenges drive the evolution of larger brains—not just in mammals but across diverse animal groups, including fish.

You can find the original article "Population density drives concerted increase in whole brain volume in a wrasse species Coris batuensis" here

The last author, Redouan Bshary, is associated with the University of Neuchâtel. You can explore his lab's research and publications here.