To survive in the competitive environment of the coral reef, fish need to be adaptable. Those with the ability and the intelligence to learn and to adapt their behavioral strategies are the most likely to come out on top.
The image that many people conjure up when the question of fish intelligence arises is that of the goldfish's three-second memory. Yet all the evidence shows that goldfish -- and indeed all species of fish -- have substantially greater memory than this, as well as a remarkable capacity for learning. The fast-paced life of the coral reef presents enormous challenges for fish. Each day is a continual round of risks and rewards, where fish have to negotiate predators and competitors while seeking out mates and feeding opportunities. To succeed in such an environment, fish need to adapt and learn throughout their lives.They must memorize what constitutes a threat, where to find food and shelter, and be able to recognize individual mates and rivals. Here, we will be looking at the various remarkable ways fish demonstrate intelligence, putting to rest the old myth of fish as mindless creatures.
Can fish really learn?
Yes. 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 the behavior of Pavlov's dogs. They learned that the ringing of a bell meant that food would shortly arrive and responded by salivating expectantly.
In the wild, fish often have to make connections between events in this way. For example, they must learn that the threatening "growl" of a neighboring territory-holder on the reef may precede an attack; that a drop in atmospheric pressure can foretell a storm, meaning that they should seek the shelter of deeper water; or that the presence of coral reproductive pheromones in the water means that, somewhere nearby, a food bonanza is available.
How else can fish learn?
As well as this ability to learn that two events are connected, fish can also learn to associate an action with a consequence. This is exactly the same process by which performing animals, such as sea lions, learn that if they jump through a hoop they will be presented with a food reward. On the reef, fish have learned that if they present themselves at a cleaning station, they will (hopefully) be attended to by a cleaner wrasse or a cleaner shrimp that will pick them clean of their parasites. Another example is the way fish can learn to avoid a particular prey item because it is unpalatable, as happens sometimes when angelfish come across unfamiliar species of sponges.
Fish are extremely flexible in this regard and can be taught a host of different actions and consequences in the laboratory. Scientists use this ability to 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 differentiate between levers based on their color or shape. This tells us much 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.