New research reveals fish are smarter than we thought

A new study published in the online journal PLOS ONE has reported the first evidence that fish are able to visually process multiple objects simultaneously. The discovery, researchers say, is proof not just that fish are more intelligent than their reputation for a “three-second memory” suggests, but may pave the way for medical advances that could help in stroke rehabilitation and in treatments for attention deficit disorders.

The study, conducted by researchers at the University of Bath and Queen Mary University of London, is the first to identify “parallel visual search”-the ability to pick out one object among many-in zebrafish. Visual search involves an active scan of an environment in order to look for just one object or feature. In everyday life we might relate to this in searching for an item on a supermarket shelf, looking for friends in a crowd or even identifying ‘Where's Waldo?'

Given the benefits of visual search in finding a mate, spotting a predator or searching for prey, the research team suggests that doing this efficiently by ignoring distracting items should be common among species. Yet up until this point it had only been identified in primates, rats and pigeons. Without the frontal part of the brain in the neocortex, it was assumed that fish would have to examine every item, one after the other, to find the target, rather than assess the whole scene together.

As part of the study, 11 adult zebrafish were presented with different visual stimuli in the form of different-colored circles on a computer monitor over a period of six days to assess their visual processing abilities. Scientists taught zebrafish to associate food with a red disc and then placed that disc among other distracting discs.

“Although vision seems simple and quick, it involves a lot of computational power to figure out where things are in a crowded environment,” says Michael Proulx, BSc, MA, PhD, of the University of Bath's department of psychology and lead author of the study. “It is incredible to discover that the zebrafish brain, with its small size and simple structure, can seemingly find a target visually without getting slower. No matter how many items we added to the scene to distract the fish, they had no problem responding at the same speed every time.”

The zebrafish is an excellent model organism to study behavioral genetics and neurobiology thanks to its smaller brain and transparent skin, Proulx says. “Now that we have discovered their mental sophistication, there is a great opportunity to discover the neural code and genetics of how humans pay attention, and apply those findings to treatments for those with ADHD or strokes,” he says.

Matthew Parker, PhD, of Queen Mary University of London, says fish are more complicated than they appear.

“Fish don't deserve their reputation as the stupid branch of the animal family tree. The more research we do, the more we find out that they are capable of quite complex learning and problem solving,” he says. “This could be because being part of a shoal requires complicated interactions with their environments and quick processing of large amounts of information. Zebrafish are genetically surprisingly similar to humans and are incredibly useful to our studies of how genes influence addiction and psychiatric diseases, among other things.”

The research adds to growing knowledge of fish intelligence that suggests they are capable of much more than scientists previously thought, the authors say. Other studies have found that fish are able to pick the larger of two groups of objects, count up to at least four and have comparatively lengthy memories.