According to the Canadian scientists, who studied African Cichlids, a popular aquarium species, fish demonstrate several complex behaviours, including aggression, causing the scientists to predict that they could be capable of advanced memory tasks.
In the study, each fish was trained to enter a particular zone of the aquarium to receive a food reward, with each training session lasting twenty minutes. After three training days, the fish were given a twelve day rest period, and were then reintroduced into their training arena and their movements recorded with motion-tracking software.
The cichlids preferred the area where the food reward was given, suggesting that they recalled the previous training experiences. Furthermore, the fish were able to reverse this association after further training sessions where the food reward was associated with a different stimulus.
Lead scientist Dr Trevor Hamilton said that fish that remember where food is located have an evolutionary advantage over those that do not, and if they were able to remember that a certain area contains food without the threat of a predator, they will be able to go back to that area. Decreases in the availability of food would promote the survival of species that can remember the location of food sources.
The researchers are now investigating whether the strength of fish memories are affected by environmental conditions or pharmacological drugs.