Fish intelligence
However, fish still display intelligence that cannot be explained through Pavlovian and operant conditioning, such as reversal learning, novel obstacle avoidance, and passing simultaneous two-choice tasks.
Australian biologist Culum Brown has argued that fish may give the appearance of being less intelligent than they are due to differences between aquatic and terrestrial environments.
The largest part of it is a special structure called the valvula, which has an unusually regular architecture and receives much of its input from the electrosensory system.
[21] Crimson-spotted rainbowfish can learn how to escape from a trawl by swimming through a small hole in the center and they remember this technique 11 months later.
[24] Several fish species are capable of learning complex spatial relationships and forming cognitive maps.
[30] Several species of wrasse hold bivalves (scallops and clams) or sea urchins in their mouth and smash them against the surface of a rock (an "anvil") to break them up.
[31][32] This behaviour in an orange-dotted tuskfish (Choerodon anchorago) has been filmed;[33] the fish fans sand to unearth the bivalve, takes it into its mouth, swims several metres to a rock which it uses as an anvil by smashing the mollusc apart with sideward thrashes of the head.
[35][36] Whitetail damselfish clean the rock face where they intend to lay eggs by sucking up and blowing sand grains onto the surface.
[40] In one laboratory study, Atlantic cod (Gadus morhua) given access to an operant feeding machine learned to pull a string to get food.
There appear to be very few to no observed behaviors of fish using tools in a fashion similar to humans, but instead altering water flows in ways that benefits their survival.
Two species, the giant mudskipper (Periophthalmodon schlosseri) and the walking goby (Scartelaos histophorus), build a special chamber at the bottom of their burrows into which they carry mouthfuls of air.
[55] Male sticklebacks are well known for their habit of building an enclosed nest made of pieces of vegetation glued together with secretions from their kidneys.
Some of them adorn the entrance of the nest with unusually colored algae or even shiny tinfoil experimentally introduced in the environment.
[56] Foam nests, made up of air bubbles glued together with mucus from the mouth, are also well known in gouramis and armoured catfish.
Furthermore, because the same regions of the brain were involved as in mammals, the study suggests oxytocin-based empathy may have evolved from a common ancestor many millions of years ago.
However, most of the observations of deception can be understood as instinctive patterns of behavior that are triggered by specific environmental events, and they do not require a fish to understand the point of view of other individuals.
Bowfin (Amia calva) males caring for their free-swimming fry exhibit a related distraction display when a potential fry-predator approaches; they move away and thrash about as if injured, drawing the predator's attention toward himself.
[65] In the Malili Lakes of Sulawesi, Indonesia, one species of sailfin silverside (Telmatherina sarasinorum) is an egg predator.
[67] In Lake Malawi, the predatory cichlid Nimbochromis livingstonii have been seen first remaining stationary with their abdomen on or near sand and that then dropping onto their sides.
They turn over onto their sides at the bottom of the sinkholes they inhabit and remain immobile for as long as 15 minutes, during which they attack the small mollies that come too close to them.
In 1999, off the coast of southeastern Brazil, one juvenile comb grouper was observed using this tactic to catch five small prey in 15 minutes.
[73] In the coral reefs of the Red Sea, roving coralgrouper that have spotted a small prey fish hiding in a crevice sometimes visit the sleeping hole of a giant moray and shake their head at the moray, and this seems to be an invitation to group hunting as the moray often swims away with the grouper, is led to the crevice where the prey hides, and proceeds to probe that crevice (which is too small to let the grouper in), either catching the prey by itself or flushing it into the open where the grouper grabs it.
[76] Mosquitofish (Gambusia holbrooki) can distinguish between doors marked with either two or three geometric symbols, only one of which allows the fish to rejoin its shoalmates.
[83][84][85][86] A laboratory study with zebra mbuna and ocellate river stingray has demonstrated that these fish can add and subtract 'one' from 2, 3, or 4.
The bluestreak cleaner wrasse (Labroides dimidiatus) performs a service for "client" fishes (belonging to other species) by removing and eating their ectoparasites.
This system has been the subject of extensive observations which have suggested cognitive abilities on the part of the cleaner wrasses and their clients.
[100][101] Cleaners give the impression of trying to maintain a good reputation, because they cheat less when they see a big audience (a long queue of clients) watching.
[102] Cleaners sometimes work as male-female teams, and when the smaller female cheats and bites the client, the larger male chases her off, as if to punish her for having tarnished their reputation.
[104] Gordon Gallup, the originator of the test, believes that the results are best explained by the fish having instincts to scrape off parasites.
When starved for 24-h before the feeding test, they doubled the number of pellets stocked (14 on average); the underside of their heads bulged under the load.
