Fish are not the mindless automatons that they are often portrayed as. They often have complex social lives, take great care of their young, and sometime pair for life.
People amuse themselves when they joke about fish having short memories. However, the truth is quite different. Fish would not be able to function if they were not able to learn to avoid previous dangers, navigate, or in the case of salmon, return to their place of birth. Several experiments, where fish learn mazes, and remember frightening events, provide evidence for a capable memory. Anglers often claim that fish can be quickly hooked again because they cannot feel pain, or forget about their previous ordeal. Anglers themselves forget - they forget that the whole purpose of their "sport" it to outwit a simpler creature by sly and unfair means.
COOPERATIVE HUNTING BETWEEN
GROUPERS AND MORAY EELS
Groupers cooperate with moray eels in hunting other fish. Groupers are adept at hunting in open water, while moray eels are able to find prey in crevices. The groupers swim to resting eels and invite them to hunt by shaking their heads. Scientists (Bshary, 2006) have observed the partnership for up to 44 minutes.
FISH use TOOL
It was once thought that only humans used tools. However, other animals, such as chimpanzees and birds have been observed using them. The Sydney Morning Herald reported, that off the Great Barrier Reef, tusk fish were seen using rocks to break open cockle shells.
ANGELFISH LEARN MEAL TIMES
Scientists in Spain were able to teach angelfish to come to different parts of a tank at different times of the day to feed.
The fish learn to go to one corner in the morning and the opposite corner in the afternoon
JUDGING MESH SIZE BY WATCHING OTHER FISH
Haddock were taught to swim across a pool for food. A large mesh net was then put across the area that the fish had to swim through.
The mesh got smaller each time.
Fish were able to learn whether they could make it through by waiting and watching other more experienced fish try it first (Glass,1992).
FRENCH GRUNT LEARN ROUTE BY WATCHING OTHERS
The French grunt, a coral reef fish, at twilight, follows traditional migration routes between its daylight nesting site and the night time feeding area. The routes can be complex and a kilometre long. Researchers moved one group of fish from one population to another. The transplanted fish, after only two days, were able to find their way by watching the established population, and were still able to do so on their own when the established fish were themselves removed (Helfman, 1984).
SEA BASS TO PUSH A LEVER TO OBTAIN FOOD
OTHER BASS WATCH AND LEARN
Scientists in Strasbourg were able to train sea bass to push a lever to obtain food. Other bass were allowed to watch this.
When they were given the opportunity to press the lever themselves, they were then much quicker to learn
how to do it. (Anthouard, 1987)
FRILLFISH GOBY LEARN LAYOUT POOLS FOR LOW TIDE
The frillfish goby at low tide can be trapped in a small pool. When prodded, the fish were able to jump to other pools with extreme accuracy, sometimes jumping up to six times to return to open water. The fish had been able to memorize the layout when the sea had been at high tide (Aronson, 1971).
MINNOWS LEARN THE DANGER OF PIKE FROM WATCHING OTHERS
Fathead minnows cannot recognise the predatory nature of pike, unless they have had an encounter with one. Scientists introduced the smell of pike into the water where some minnows had experienced the danger of pike, and some had not. The inexperienced minnow learnt to react with fear from the experienced fish. When the experienced fish were removed and the smell was introduced again, the fish still felt the danger - even though they had never seen a pike (Mathis, 1996).
Salmon have magnetic sensors in their heads. These cells are connected by a special nerve to the brain to detect magnetic anomalies in their environment. Salmon use this ability to navigate using the earth's magnetic poles in long journeys to their spawning grounds. Rainbow trout and leopard sharks can also detect magnetic fields (Reebs, 2001).
TUNA FIND THEIR WAY BACK AFTER 35 KILOMETRES
In New Zealand, small mottled triplefins normally spend their adult life in a two-metre-square area of water. Some of them were transported, in an experiment, more than 700 metres along a rocky reef. Most were able to find their way back after 4 to 6 days. Other fish have found their way back from longer distances: flathead catfish, 1 kilometre, sunfish and bass, 3.5 kilometres, yellowtail rockfish 22 kilometres, and skipjack tuna 35 kilometres (Reebs, 2001).
BOUNDARY WALLS BUILT
When mudskippers start to live at high densities, they build mud walls 3 to 4 centimetres high at the boundaries to their territories (Clayton, 1986).
NESTS FROM GLUE, MUD AND BUBBLES
Male sticklebacks build nests of plant material with the help of a glue produced by a special gland. Gouramis build nest from air bubbles and then blow them to the surface (Reebs, 2001).
AIR BROUGHT BACK TO BURROW
A species of mudskipper in South East Asia builds burrows. It can take air into its mouth and then dive down into the burrow to diffuse it into the water. This can also help the young, who are born in the burrow (Ishimatsu, 1998).
If a Siamese fighting fish senses danger, he shakes his pectoral fins close to the surface of the water. This wave can be detected by his young, who then swim to him.
He then sucks them into his mouth for protection and carries them safely back to the nest (Reebs, 2001).
RAINBOW TROUT WATCH OTHER TROUT THROUGH PARTITION
TO LEARN SOCIAL ORDER
In an experiment, individual rainbow trout were able to observe the interaction of two other rainbow trout behind a partition. The observing fish, when later put with one of the fish, was able to realise whether that fish was more likely to be dominant or not, and acted accordingly (Johnsson, 1997).
FISH TALK TO EACH OTHER
Some fish can produce sounds to communicate with each other. Swim bladders can be made to vibrate by rapid contractions of special muscles, in, for example, the oyster toadfish. Other fish can grunt, croak, hum, moan, thump, buzz, click, and howl. These sounds may be territorial during the mating season, such as by the mormyrid fish, and the intertidal plainfish midshipman.
This last fish is called the Californian singing fish by fishermen. It hums to attract females, lasting sometimes for as long as an hour without pause. The John Dory grunts loudly when it is lifted out of water (Reebs, 2001).
MOST RAPID FORM OF COMMUNICATION IN THE ANIMAL KINGDOM
Elephant fish can communicate with each other using electrical signals. The response time from one fish to another is extremely short - approximately 12 milliseconds. This is probably the most rapid form of communication in the animal kingdom (Reebs, 2001).
MEMORY MYTH EXPOSED
10 DAYS MEMORY OF ZEBRAFISH
In Toledo in the USA (Williams, 2002), scientists were able to train zebrafish to learn to position themselves at one side of a tank, according to cues (light tapping on the tank). They were able to repeat this after 10 days.
BLIND CAVE FISH MAP THEIR ENVIRONMENT
Scientists at Oxford University in England (Burt de Perera, 2004) tested blind Mexican cave fish in a laboratory by changing the order of landmarks. The fish quickly were able to detect the change through their lateral line and store a map of their surroundings in memory.
FEAR AND MEMORY
Trout were taught by researchers in Canada (Yue, 2004) to avoid a net. The fish remembered to avoid the net on the first occasion. After seven days of no testing, the fish still responded in the same way. The memory may have lasted longer but was not tested. The research demonstrates both memory and fear in the fish.
SALMON REMEMBER THE STREAM OF THEIR BIRTH
Adult salmon find the stream of their birth, after returning from the sea. They follow the trail of odour learnt several years earlier (Reebs, 2001).