This fish has no cerebral cortex in its brain, but it acts like it does - study

The human cerebral cortex, which is located in the outer layer of the brain is involved in many high-level functions such as reasoning, emotion, thought, memory, language, and social consciousness. 

The tropical archerfish (also known as spinner fish) have no cerebral cortex, but to the surprise of University of Haifa researchers, this species shows prosocial behavior towards their “friends” and doesn’t feel “cheated.” 

The new study from the University of Haifa published in the journal Communications Biology entitled “Prosocial behavior in competitive fish: the case of the archerfish,” found that archerfish behave like animals that actually have a cerebral cortex even though they don’t have that part in their brains.

Archerfish: Using brain parts they don't even have?

“Apparently, these social traits are important for survival in both cooperative and competitive societies, such as the fish we studied,” said Dr. Orit Nafcha, a postdoctoral in social cognition and neuroscience from the University of Haifa who led the study. “People function most of the time in social contexts and depend on others for survival, so understanding the intentions and behavior of others is an important ability that allows us human, to survive successfully in a social environment.”

Humans are social creatures, demonstrate prosocial behaviors, and are sensitive to the actions and consequent payoff of others, they wrote. “This social sensitivity has also been found in many other species, though not in all. Research has suggested that prosocial tendencies are more pronounced in naturally cooperative species whose social structure requires a high level of interdependence. Our study challenges this assumption by demonstrating, in a lab setting, that archerfish –competitive by nature – preferred targets rewarding both themselves and their tankmates, but only when the payoff was equal. With no tankmate on the other side of the partition, they showed no obvious preference. Finding evidence for prosocial behavior and negative responses to unequal distribution of reward to the advantage of the other fish suggests that in a competitive social environment, being prosocial may be the most adaptive strategy for personal survival, even if it benefits others as well.”

According to the researchers, research literature today shows a bias for focusing on the involvement of the “higher” areas in the brain in the study of social behaviors. This neglects the possible contribution of the subcortical areas that developed evolutionarily in earlier stages. 

Comparing fish cognition and behavior to that of primates has many challenges, said Nafcha. “Most studies have used different experimental manipulations and different dependent variables when studying non-primates. We specifically selected archerfish to serve as our model because of their remarkable ability to shoot down insects found on foliage above water level. In the present study, Nafcha, research student Dana Vilker, Prof. Simone Shamay-Tsoory, and Prof. Shay Gabbai from the School of Psychological Sciences and the Institute for Information Processing and Decisionmaking of the University of Haifa decided to examine the evolutionary basis for the behaviors of social cooperation and social fairness and how these behaviors are expressed in competitive species lacking cortex. 

They used a double aquarium divided into two with a transparent partition, where on each side was an archerfish that couldn’t pass from side to side and each fish received food only on its side. In the first experiment, the fish were given the opportunity to choose between a non-social target (a black starfish) that when he spits on, only he receives a reward, and a social target (a red starfish) that when the fish spits on it, he receives food; in addition, the other fish found beyond the partition receives food. The colors were changed in the second stage of the experiment, each color was used both for personal reward and for shared reward to avoid an alternative explanation according to which the fish prefer a certain color and not necessarily a social behavior. 

In both phases, all the fish in the study always preferred the social goal – food for both them and their friend beyond the glass. Finally, in the last experiment, the researchers looked at what happens when the passive fish gets more food than the active fish. In this condition, the social target rewarded the spitter with one piece of food and the passive fish with two pieces of food, while the non-social target rewarded only the archerfish with a single piece of food. At this point, the archerfish stopped choosing the social goal, which would reward their friend even more. 

The results of all the experiments show that even fish living in a competitive social environment will exhibit social behavior as long as the reward is equal but will stop doing so if the other fish earns more than them. “The study shows for the first time in lab conditions that the competitive archerfish behaves in a pro-social manner under certain conditions and stops behaving this way when the product creates an unequal situation.