The Evidence is in: Fish are Intelligent!
In a Nature paper, published in 2007, the lab of Dr. Russell Fernald at Stanford University showed that fish are capable of inferring which fish to fight for territories based on observations of previous interactions with other territorial fish . After observing a series of interactions between several males, they are able to use deductive reasoning to infer an implied dominance rank among the observed individuals. Later on, in 2010 the Fernald lab showed that females are able to remember which males had won or lost in a fight, and when given a choice, preferred winners over losers .
Work performed by Dr. Trevor Hamilton and Erica Ingraham at MacEwan University has shown that fish can remember where they are receiving food 12 days after the training period had ceased (unpublished data). It makes sense that fish would be capable of remembering where to find food or mates, how to avoid predators, or where to best lay eggs, as these decisions significantly impact fitness and reproductive success.
Figure 1 (right): Image of a recorded path from video tracking software used at in Dr. Hamilton’s Lab at MacEwan University. Tracking plot shows fish spend more time in areas where they have been previously fed than other areas of the tank.
Social learning is another interesting topic currently garnering attention in the field. Dr. Alex Jordan is a Post-Doctoral researcher at The University of Texas. He is currently working to understand the social facilitation of learning in multiple fish species. Dr. Jordan is exploring how group dynamics and an individual’s position within the social hierarchy, or social circumstances, affect both their learning abilities, and teaching abilities. ‘Animals don’t exist in dyads’ Dr. Jordan says, and there are ‘universal social truths’ shared across vertebrates.’ Here, his work controls for a variable ecological environment while exploring how ‘information is communicated and propagated in a realistically complex social group.’
In short, groups of fish are placed in a large aquarium where a stimulus is followed by a food reward. Some species are capable of learning to respond to the stimulus in just a few days, and remember it many weeks (or even months) following the training period. High-tech video tracking software follows individual fish and allows discernment of their stimulus response behaviors (unpublished data). While the story here is not yet written, there are trends that dominant individuals are poor teachers compared to subordinates. He has also seen that fish learn more quickly when other fish that have previously learned the task are present. Although this could be due to a variety of reasons, social learning seems the most plausible.
Figure 2: A fish observing aggressive interactions, which sees fish ‘A’ is dominant to fish ‘B’ and Fish ‘B’ is dominant to fish ‘C’ and so on, is able to deduce that fish ‘A’ is dominant to fish ‘E’ and ‘D’.
Fish are even capable of transmitting cultural traditions comparable to other vertebrate groups. It has been hypothesized (especially in long lived fishes) that migration routes to spawning grounds are taught to younger individuals by older more experienced fish. The loss of some of these larger and older fish due to commercial fishing may have led to population declines with species such as the cod .
While not all fish species have equal brainpower, several are clearly capable of complex cognitive learning. Many reef fishes and cichlid species commonly kept in aquariums are among those well-studied groups shown to be intelligent. So the next time you look at your fish and you think it might recognize you. You might be right!
1. Grosenick, L., T.S. Clement, and R.D. Fernald, Fish can infer social rank by observation alone. Nature, 2007. 445(7126): p. 429-32.
2. Desjardins, J.K., J.Q. Klausner, and R.D. Fernald, Female genomic response to mate information. Proceedings of the National Academy of Sciences of the United States of America, 2010. 107(49): p. 21176-21180.
3. Brown, C., Fish intelligence, sentience and ethics. Anim Cogn, 2014.