Freshwater Fish Can Learn and Demonstrate Intelligence

Are fish intelligent? Most people think not, believing that goldfish have only a three-second memory. Yet evidence shows that goldfish — indeed all fish species have a far greater memory than this, plus a remarkable capacity for learning.

Learning — the modification of a response as a result of experience — has been shown in animals ranging from humans to invertebrates. It allows individuals to adapt to different situations and to behave more efficiently, but in order to learn, an animal must have some kind of memory.

Can fish really learn?

A basic type of learning that has been demonstrated in fishes is the ability to connect two different events. A simple example is the way that aquarium fish associate the appearance of the fishkeeper with the arrival of food. On seeing the former, the fish often begin to swim excitedly at the front of the tank, expecting the imminent addition of food. This is akin in many respects to Pavlov's dogs, where the dogs learned that the ringing of a bell meant that food would shortly arrive and would begin to salivate expectantly.

But this is by no means the only connection that fish are able to make. Experiments using male blue gouramis showed that the fish quickly learned that a light being switched on would be followed by the appearance of a female. When the males saw the female they began to display. In time, the males started to display as soon as the light was switched on.

Experiments on feeding behavior in archerfish (Toxotes jaculatrix) produced a similar response. Archerfish are famous for their ability to spit water at insect targets with incredible accuracy, shooting them down and seizing them as they struggle on the water surface. When researchers switched on a small light before adding an insect to the aquarium the fish learned to connect the two events, and after a short period of time would start to spit water as soon as the light came on.

Although this may seem to bear no relation to the events that a fish might experience in the wild, very often two events are related. It has been observed that fish often growl at one another before they attack. Learning that growling usually precedes an attack means that fish have the chance to back down before they are injured.

How else can fish learn?

Similar to Pavlovian conditioning is “operant conditioning,” where a fish can learn to relate a consequence to a particular behavior pattern. This is the mechanism sometimes used to teach animals to perform tricks — a sea lion may learn that if it jumps through a hoop it is given a reward. Fish have shown an ability to learn a wide variety of tricks in this way, ranging from pushing a lever to obtain food on demand to playing underwater football. Although performing tricks like this may seem frivolous, there is a serious, scientific basis for studying operant conditioning in fishes. By using rewards to encourage a fish to perform an action, we can study, for example, how long it takes the fish to learn under different circumstances, such as different temperatures or oxygen concentrations. By presenting them with a choice of levers to press where only one provides a food reward, we can look at their ability to discriminate levers based on their color or shape, which tells us a great deal about their evolution. Ultimately, we can also probe the furthest extent of fish intelligence to find out the limits of their ability to learn and to remember. One thing is for sure — the ability to learn new skills should finally lay to rest the mistaken notion that fish have a three-second memory.

Which fish are the most intelligent?

Clearly there is no fish IQ test, but we can make general statements. For example, large, long-lived fish tend to be smarter than small fish with a rapid life cycle, such as guppies. Generally speaking, omnivores and fish that provide parental care also often have real brain power to cope with the tasks that they perform in their lives. Many cichlids and catfish and some gouramis fit the profile and are surprisingly intelligent being capable of flexible behavior, learning new skills and retaining information for long periods.