Article: Abudayah, W. H. and Mathis, A. (2016), Predator recognition learning in rainbow darters Etheostoma caeruleum: specific learning and neophobia. Journal of Fish Biology. doi:10.1111/jfb.13061
I have written about schools of fish in the past and why they swim the way they do. Now I want to talk about school in the way humans think of it– learning.
Mammals spend time with their young, teaching them necessary skills to survive. Therefore, mammals obviously have the ability to learn. Fish, on the other hand, typically do not spend any time with their young. Once the eggs are laid, they are on their own, suggesting that these fishes must have instinctual knowledge which allows them to survive. But does this mean they never learn? Can they learn? Can they retain learned information permanently?
These are the type of questions that scientists studying fish learning want to address.
Studying Fish Behavior
The overall goal of this experiment was to determine if rainbow darters (Figure 1) would learn to recognize a never-before-seen predator as a threat. Many fish produce a chemical from their skin when they are attacked which diffuses into the surrounding water, alerting nearby fishes that there is a predator present. The scientists in this study used this chemical cue to entrain a fright response in the fish. The researchers hypothesized that if this chemical is present at the same time as the scent of a never-before-encountered animal, a fish capable of learning will associate the scent of this new animal with the threat of danger. If this is the case, the researchers predict that fish later exposed to just the scent of this new animal will respond in fear or avoidance. However, if the fish are not able to learn, they will never recognize this new predator as a threat.
Before conducting the main experiment, the researchers had to make sure that rainbow darters do not exhibit an innate fear response to the scent of any new animal. First, fish were exposed to the scent new animals that they do not naturally encounter in the wild. Fish exposed to the new animals and fish exposed to a control (a blank water sample) behaved no different from one another, therefore suggesting that the fishes were not inherently afraid of new animals in their environment.
A treatment group of 32 fish were exposed to the scent of the ringed salamander along with the fish alarm cue scent to train the fish to recognize the scent of a ringed salamander as a threat. These fish were also exposed to the scent of a western rat snake, but in the absence of the fish alarm cue. This was done to determine if fish were able to learn to recognize specifically the salamander as a threat, or if they would respond in fear to all foreign scents. The untrained group of 32 fish were exposed to the scent of both predators alone, with no alarm cue included. These fish should not respond in fear to the scents of these predators in the future. Then, both groups were tested a short time after training (2-7 days) and again a longer time after training (32-40 days) by presenting just the scent of the respective predators to the fish to see how they would respond.
After only a few days, the trained fish responded negatively to the scent of both the salamander (Fig. 2a) and the snake (Fig. 2b). This is known as “neophobia”. You can think of it as the fish being on high alert, ultra-sensitive and cautious to any new signals. When retested 30+ days after training, the trained fish still responded negatively to the salamander (the animal they had been trained to recognize as a predator; Fig. 2c) but did not respond negatively to the snake (the animal they had not been trained to recognize; Fig. 2d).
This is not the only study on fish cognition. In fact, there have been hundreds of other studies since 1873 that have demonstrated the ability of many different species of fish to learn a wide variety of skills. We go to school to learn. Fish, whether in a school or not, are fully capable of learning. Despite their extensive innate skills and lack of any formal education from parents or teachers, fish absolutely have the capacity to learn new skills. There’s even some evidence that fish have a peak period of time in their lifespan where they are most capable of learning, just like us. But this a subject for another OceanBites post…