Fishes Remember Being Caught For A Long Time

In the wild, where environmental conditions often vary and challenge their inhabitants to their limits, memory serves a vital role in helping animals survive and reproduce successfully. The cognitive ability enables the storage and retrieval of various information, and we know that factors such as uncertain food availability and risks for predation could have played a role in the development of long‐term memories, shown to span from a few months to decades in nonhuman animals. Although fishes have been shown to retain information from a few weeks up to several months, studies revealing high cognitive capacities in fish are still scarce. In this study, researchers attempted to add to the pool of information by confirming that wild cleaner fishes can remember being caught. 

Generally, it is said that the ‘powerfulness’ of a given event can increase memory retention, where long‐term memories are typically ones of various adverse events. Examples include salmon and carp who still exhibit “hook-shyness” a year after having been caught. A previous study with cleaner fish also showed that they avoided nets and hid in crevices while researchers tried to recapture them 4 weeks after the time they had caught and marked them.

The present study supplemented the results of the above-mentioned research in that the acquired data suggests that cleaner fishes can remember a single negative experience for 11 months. The researchers also confirmed that the negative association was made with the net, not the divers, as the individuals who would hide with the net in sight, reemerge when it was removed and only the divers remained. The choice of observing cleaner fish is a clever one, as it’s generally really difficult to evoke hiding in the species, with the courageous fishes even approaching and entering predator mouths regularly. In other words, such a strong response is truly significant in these otherwise brave animals.

These long-term memory capabilities are similar to long‐term memory retention proposed by other researchers to cause escape responses in rainbowfish when they encounter trawls and the aforementioned hook‐shyness in salmon and carp. All of these are memories of highly aversive, life‐threatening events. On a more positive note, the researchers report that one recent study has shown that sharks may also learn how to avoid being caught after having experienced the ordeal of catch‐and‐release prior.

Be it for fishes being sold alive, or captured in catch-and-release fishing, the findings of this and similar studies suggest that these animals carry stressful memories with them, potentially for a very long time. Animal advocates will surely recognize just how such a state of mind adds to the overall stresses that exploited fishes experience. Although we are far from a place in time when the basic welfare of fishes is ensured, this study certainly suggests that we should be advocating for the mental wellbeing of these wonderful water-dwelling earthlings.