Social Learning by Fish
Fish seldom live out of contact with others, be they of the same species or entirely different. The actions of other fish in the same environment can provide information for any fish that tunes in to what is happening. For example, if an observer fish sees panic spreading through the other fish in the locality, it may well indicate that a predator is active in the area, so it can use this information to shelter. Similarly, if one fish sees others pecking at the substrate and apparently feeding, it can swim over to join the crowd at the feast.
Where do fish get their information?
All animals have their own private information, based on their own learning, exploration, and experience. But gaining private information takes energy and time -- to learn everything about its environment a fish would have to investigate all of it, which would usually be a considerable task. As a result, fish often learn from others and use others' experiences to help them to make decisions. This public information is less reliable than finding out things for yourself, but is a much easier option. For example, male swordtails are known to watch fights between other males, a process known as "eavesdropping". They can then judge the strength of each combatant, perhaps avoiding a contest with the winner but taking the opportunity to "kick" the loser while he is down.
Can fish learn from other fish?
There is plenty of evidence to show that fish can, and do, learn from one another. This process is known as social learning. Guppies, for example, can learn from one another about the location of a hidden food source and in this way, the information spreads throughout entire schools. In fact, social learning in guppies is so powerful that once the fish are taught to swim a lengthy and complicated route to their food patch, this spreads through the school and persists for considerable amounts of time, even though a simpler and shorter route exists.
Female mollies (Poecilia sphenops) take a great deal of notice of the mate choices of other females, very
often choosing to mate with the same male that they have seen the other females mate with. By doing this, the females are trying to ensure that they are mating with a real hotshot. The benefit to them is that their offspring will carry the hotshot's genes, and their sons will hopefully be as desirable as their father -- meaning that future females will be sure to choose him.
Fish also learn socially about danger: if a fish sees one of its conspecifics fleeing from a particular kind of predator, it quickly learns to avoid that species itself. Juvenile cichlids are also thought to learn from their parents in the same way about what is, and what is not, a danger to them. In relation to this, fish raised by parents seem to recognize predators far better than those raised without parental care. The parental catfish Bagrus meridionalis are also thought to teach their offspring what to eat by bringing certain kinds of invertebrate prey to the nest and spitting out the chewed up pieces into the midst of their hungry brood.
Social learning in the aquarium
Social teaming is a common phenomenon in the aquanum -- as soon as one fish detects that food has been added to the tank, the news travels like wildfire! A similar situation exists when new inhabitants are added to the tank. If the existing fish are accustomed to being fed in the same part of the tank, newcomers can learn where this is, even without actually seeing the food, by picking up cues from their tankmates' behavior.