To most people, a specific fish species would be the same whether it was found at the shoreline or in the middle of the ocean. But according to research published last week in the journal Proceedings of the Royal Society B by researchers from the University of Guelph, these vastly-different habitats can influence a fish’s brain size.

Image Credit: Cephas/Wikipedia

Citing the results of the study, pumpkinseed sunfish that live in busier and more complex shoreline-centric habitats sport brains that are, on average, 8.3% larger than those living in simpler open-water habitats. According to the researchers, the varying brain sizes could correspond with significant lifestyle differences between the two types of habitats.

"Habitat indeed has an effect," explained study lead researcher Caleb Axelrod. "That was a surprising finding."

Related: These weird fish live in some of the deepest parts of the ocean

Captivatingly, intraspecific brain size discrepancies are typically associated with a particular region of the brain rather than the entire brain overall; but that wasn’t the case here. Instead, littoral sunfish exhibited larger brains overall than their pelagic counterparts, which made the debacle much tougher to elucidate.

Individual components of the brain contribute to specific types of behavior, and so a more substantial brain component in one animal compared to another denotes that the animal with the larger package does its job more efficiently in response to specialized conditions, such as what it might encounter in the surrounding environment.

The shoreline-centric fish exhibited larger brains overall, which threw a wrench in the works. The situation became even more curious when the researches discerned that sunfish from both habitat types had similarly-sized heads, regardless of brain size.

Given the circumstances, the researchers suggest that the oversized brains in the shoreline-based sunfish might not play a specialized role. Instead, perhaps it offers the additional cognitive capacity to respond to the busier environment than a pelagic sunfish would ever deal with in the open water.

Related: Can effective fisheries management prevent the extinction of marine fish stocks?

As of this writing, it remains to be seen if similar patterns exist in other fish species or if this is specific to the pumpkinseed sunfish. The researchers conclude that it’s too early to tell why one fish has a larger brain than the next, and it’s even more challenging to discern how this impacts the animal’s natural behavior or lifestyle.

It should be interesting to watch new studies pick up where this one left off. In time, perhaps researchers will discover some answers to the questions that remain.

Source: EurekAlert, Proceedings of the National Society B