Fish Perception and Communication

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Bony fish eye: Fish have a refractive index gradient within the lens which compensates for spherical aberration; Unlike humans, most fish adjust focus by moving the lens closer or further from the retina; Bony fish do so by contracting the retractor lentis muscle

Fish sense using vision (See Below), sound (See Below), infrared-heat, ultraviolet and polarized light sensing, touch, vibrations, chemicals, electric signals and magnetism. According to Animal Diversity Web (ADW): Fish perceive the external environment in five major ways — vision, mechanoreception, chemoreception, electroreception and magnetic reception, and to humans several of these sensory systems are entirely alien. Many types of perception are also used by fish to communicate with individuals of the same (conspecifics) or other species (heterospecifics). [Source: Nicholas White, Animal Diversity Web (ADW) /=]

Most fish have a very developed sense of smell. Their nostrils open into cups that can detect very minute amounts of chemicals in the water All fish have rods of nerve cells, called “lateral lines”, that run down their flanks and branch over the head. They have a slightly different texture from the rest of the body and consist of vibration-sensitive hairs and pores connected by a canal running just below the surface. Tiny hair cells in the lines detect difference in pressure and movements in the water and changes in dozens of meters away.

Some fish, usually inhabiting turbid environments, have specialized organs for electroreception. Several groups can detect weak electrical currents emitted by organs, such as the heart and respiratory muscles, and locate prey buried in sediment (catfish) or in extremely turbid waters (elephantfishes). Elephantfishes and naked-back knifefishes actually produce a constant, weak electrical field around their bodies that functions like radar, allowing them to navigate through their environment, find food, and communicate with mates.

A diverse range of fish orders have developed the ability to use electricity for communication: Mormyriformes (elephantfishes and Gymnarchidae), Gymnotiformes (six families) , Siluriformes (electric catfishes), and Perciformes (stargazers). The key to electrical communication is not simply the ability to detect electrical fields, but to produce a mild electrical discharge and modify the amplitude, frequency, and pulse length of the signal. This makes electrical signals individually specific, in addition to being sex and species-specific. Consequently, “electrical discharges can have all the functions that visual and auditory signals have in other fishes, including courtship, agonistic behavior and individual recognition”

A few highly migratory fishes can apparently detect earth-strength magnetc fields directly, in much the same way sensation occurs with the lateral line. While the specific mechanisms of magnetic reception are unknown, researchers have found magnetite in the heads of some tunas (e.g. yellowfin tuna) and in the nares of some anadromous salmon (subfamily Salmoninae). Presumably, magnetic perception helps fish locate long distance migration routes for both feeding and reproduction. /=\

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium ; MarineBio

Fish Vision

Four-eyed fish like this feed at the surface of the water with eyes that allow it to see both above and below the surface at the same time

Fish have eyes with parts that are similar to those of terrestrial animals and in fact fish are the evolutionary source of eyes on terrestrial animals. Fish eyes don't have eyelids because they don't need to keep their eyes moist. Fish tend to be nearsighted and most species have rods and cones, which means they can detect color. A fish eye has a totally spherical lens that corrects for refraction, or bending of light, in water and corrects fickle light conditions in the sea. Cones provide acute vision in bright light conditions while close-packed rods pull in light in dim conditions.

According to Animal Diversity Web (ADW): The eyes of fish are able to recognize a broad range of wavelengths. A species’ ability to perceive various wavelengths corresponds to the depth at which it lives since different wavelengths attenuate (become weaker) with depth. In addition to the normal spectrum perceived by most vertebrates, several shallow-water species are able to see ultraviolet light; others, such as anchovies , cyprinids , salmonids and cichlids , can even detect polarized light! [Source: Nicholas White, Animal Diversity Web (ADW) /=]

Many fishes also have specially modified eyes adapted for sight in light-poor environments and even outside of water (e.g. mudskippers). For example, several families of deepsea fishes (deepsea hatchetfishes , pearleyes , giganturids , barreleyes) have elongate (long and narrow), upward-pointing, tubular eyes that enhance light gathering and binocular vision, providing better depth perception. Also, several deepwater, midwater and a few shallow species actually have internally generated lights around the eyes to find and attract prey and communicate with other species. Light is usually produced in two ways: by special glandular cells embedded in the skin or by harnessing cultures of symbiotic luminous bacteria in special organs. /=\

Diurnal reef fish can often see more colors than humans and parts of the spectrum that humans can't discern. Their eyes are generally small and usually have a thick layer of melanin that prevents light from bouncing around inside the eye, disrupting their visual images.

Nocturnal fishes often only see in black and white. Having evolved from species that once lived in deeper water, they often have big eyes with big pupils that can perceive a lot with only a little light. It is not clear how good reef fish vision. Some species have been observed feeding on diver's bubbles, apparently confusing them for small silvery fish.

Predator fish such as barracuda and groupers are most active at dawn and dusk and their eyes contains features found in both diurnal and nocturnal fish. Some sea creatures may react to contrasts rather than colors themselves. Shrimp that are bright red and white might actually look black and white to a reef fish, who respond to the contrast not the color.

Four-Eyed Fish

Eye of a four-eyed fish: 1) Underwater retina, 2) Lens, 3) Air pupil, 4) Tissue band, 5) Iris, 6) Underwater pupil, 7) Air retina, 8) Optic nerve

Four-eyed fishes belong to the genus, Anableps in the family Anablepidae. They have eyes raised above the top of the head and divided in two different parts, so that they can see below and above the water surface at the same time. Like their relatives, the onesided livebearers, four-eyed fishes mate only on one side, right-"handed" males with left-"handed" females and vice versa. These fish inhabit fresh and brackish water and are only rarely coastal marine. They originate in lowlands in southern Mexico to Honduras and northern South America. [Source: Wikipedia[

Four-eyed fish have only two eyes, but the eyes are specially adapted for their surface-dwelling lifestyle. In early development, the four-eyed fish’s frontal bone expands dorsally allowing the eyes to be positioned on top of their head and appear bulging. This allows the fish to simultaneously see above and below the water as it floats at the surface. The eyes are divided into dorsal and ventral halves, separated by a pigmented strip of tissue.

Each eye has two pupils and two corneas filtering light onto one lens, refracting onto separate hemiretinas and processed through one optic disc.The upper (dorsal) half of the eye is adapted for vision in air, the lower (ventral) half for vision in water. The lens of the eye also changes in thickness top to bottom to compensate for the difference in the refractive indices of air versus water. The ventral hemiretina is characterized by thicker cell layers containing more sensory neurons and an increased visual acuity compared to the dorsal hemiretina.

Lateral line

The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial cells, known as hair cells, which respond to displacement caused by motion and transduce these signals into electrical impulses via excitatory synapses. Lateral lines serve an important role in schooling behavior, predation, and orientation. Early in the evolution of fish, some of the receptive organs of the lateral line were modified to function as the electroreceptors called ampullae of Lorenzini. [Source: Wikipedia]

The lateral line system allows the detection of movement, vibration, and pressure gradients in the water surrounding an animal, providing spatial awareness and the ability to navigate in the environment. This plays an essential role in orientation, predation, and fish schooling. Analysis has shown that the lateral line system should be an effective passive sensing system able to discriminate between submerged obstacles by their shape. The lateral line system enables predatory fishes to detect vibrations made by their prey, and to orient towards the source to begin predatory action. Blinded predatory fishes remain able to hunt, but not when lateral line function is inhibited by cobalt ions

The lateral line plays a role in fish schooling. Blinded Pollachius virens were able to integrate into a school, whereas fish with severed lateral lines could not.[6] It may have evolved further to allow fish to forage in dark caves. In Mexican blind cave fish, Astyanax mexicanus, neuromasts in and around the orbit of the eye are bigger and around twice as sensitive as those of surface-living fish.

Lateral line on a shark

One function of schooling among prey fish may be to confuse the lateral line of predatory fishes. A single prey fish creates a rather simple particle velocity pattern, whereas the pressure gradients of many closely swimming (schooling) prey fish overlap, creating a complex pattern. This makes it difficult for predatory fishes to identify individual prey through lateral line perception.[8]

Fish Communication

Fish communicate with vision, touch, sound, chemicals usually detected by smelling, electric signals, photic/bioluminescent, mimicry, duets (joint displays, usually between mates, and usually with highly-coordinated sounds), choruses (joint displays, usually with sounds, by individuals of the same or different species), pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species), scent marks (produced by special glands and placed so others can smell or taste them) and vibrations. [Source: Nicholas White, Animal Diversity Web (ADW) /=]

Fish are believed to communicate with each other for different reasons, such as attracting mates, orienting themselves and scaring off predators. According to Animal Diversity Web (ADW): Mechanoreception includes equilibrium and balance, hearing, tactile sensation, and a ‘distance-touch-sense’ provided by the lateral line. Chemoreception involves both smell (olfaction) and taste (gustation), but, as in terrestrial vertebrates , olfaction is much more sensitive and chemically specific than gustation, and each has a specific location and processing center in the brain.

The lateral line is composed of a collection of sensory cells beneath the scales and is able to detect turbulence, vibrations and pressure in the water, acting as a close-quarters radar. This sensation is particularly important in the formation of schools (see Behavior) because consistent positioning is essential for turbulence reduction and smooth hydrodynamic functioning. Consequently, individuals are “so sensitive to the movements of companions that thousands of individuals can wheel and turn like a single organism”. Experiments have shown that the lateral line sensation can even compensate for loss of sight in some species, such as trout. The fact that several naturally sightless fish occupy caves (e.g. cavefishes) and other subterranean environments, making extensive use of distance-touch sensation, provides further evidence. /=\

Many fishes use chemical cues to find food. Taste buds are scattered widely around the lips, mouth, pharynx, and even the gill arches; and barbels are used for taste reception in many families (most carps , catfishes and cod). However, the use of nares (like nostrils, located on the top of the head) to detect pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species) is probably the most important type of chemoreception in fishes.

Pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species) are chemicals secreted by one fish and detected by conspecifics, and sometimes closely related species, producing a specific behavioral response. Pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species) allow fish to recognize specific habitats (such as natal streams in salmon), members of the same species, members of the opposite sex, individuals in a group or hierarchy, young, predators, etc.

Lateral line organ

Some groups in dominance hierarchies even associate the scents of individuals with their particular ranking. Also, groups of closely related species, such as cyprinids , are able to detect ‘fear scents,’ which are pheromones (chemicals released into air or water that are detected by and responded to by other animals of the same species) released when the skin is broken (i.e. a predator has attacked), prompting others to adopt some type of predator avoidance behavior. /=\

Fish Visual Communications

According to Animal Diversity Web (ADW): Vision is the most important means of communication and foraging for many fish. One way fishes communicate visually is simply through their static color pattern and body form. For instance, juveniles progress through a range of color and shape patterns as they mature, and sexes are often colored differently (Sexual Dimorphism0.In addition, some fishes are quite good at identifying other species; the Beau Gregory damselfish is apparently able to distinguish 50 different reef fish species that occur within its territory. [Source: Nicholas White, Animal Diversity Web (ADW) /=]

A second way fishes communicate visually is through dynamic display, which involves color change and rapid, often highly stereotyped movements of the body, fins, operculae, and mouth. Such displays are often associated with changes in behavioral state, such as aggressive interactions, breeding interactions, pursuit and defense. A third form of visual communication is light production, found among numerous fishes in deepsea habitats.

Midwater species, such as lanternfishes , hatchetfishes and dragonfishes have rows of lights along the underside of the body, probably for mating and identification as well as foraging. Even some shallow-water species, such as pineconefishes , cardinalfishes and flashlight fish (family Anomalopidae) of the Red Sea utilize internal light sources to form nighttime feeding shoals or for other behavioral interactions.

Fish Hearing

Fish don't have outer ears. They can sense vibrations through the water with an inner ear comprised of three canals and a large sac, all of which have sensitive linings and small particles that move and vibrate. Sound moves better through water than air. Sound waves pass through the skull and reach the inner ear without the aid of a passageways like those provided by the outer ears that terrestrial animals have.

Many fish have bony connections between their ears and swim bladders and use their swim bladders as amplifiers of sound. Some have even developed special muscles that vibrate the swim bladder to produce a loud drumming noise used to call other fish.

electroreception in an elephant fish

Most fish have keen hearing ability. According to Animal Diversity Web (ADW): Detecting sound in water can be difficult because waves pass through objects of similar density. Therefore, fish have otoliths, which have greater density than the rest of the fish, in the inner ear attached to sensory hair cells.Since gas bubbles increase sensitivity to sound, many ray-finned fish (e.g. herrings , elephantfishes and squirrelfishes) have modified gas bladders and swim bladders adjacent to the inner ear. [Source: Nicholas White, Animal Diversity Web (ADW) /=]

Fish Noises

Sound production is common but not universal among fish. Cod are among the more quiet fish. Fish don't have voice boxes. They produce a variety of sound with different parts of their bodies. Sea robins, drum fish and other fish make booming, grunting and drumming noises with their swim bladders. Other fish grind their teeth or scape their fins against their bodies. Croakers make enough noise to keep fishermen away at night. Their two- and three-beat drumming sounds are produced by muscles that drum against the swim bladder.

Reef fish make quite a bit of noise underwater if you are tuned into the right frequency. Underwater noise includes groupers making a creaking door noise when they spot prey, cichlids emitting grunts, hamlet fish letting out loud squeals, the popping sound made by pistol shrimps, the crunching sound of feeding parrotfish and the grunts of damsel fish.

Stridulation, which involves rubbing together hard surfaces such as teeth (e.g. filefishes) or fins (e.g. sea catfishes), or the vibration of muscles (e.g. drums), is the most common way sound is produced. Often the latter structures have a muscular connection to the swim bladder to amplify sound. Accordingly, the swim bladder itself is the source of the most complex forms of sound production in many groups (e.g. toadfishes , searobins and flying gurnards). [Source: Nicholas White, Animal Diversity Web (ADW) /=]

Fish “Talking” and Sound Communications

In groups that do utilize sound for communication, the most common purpose is territorial (defend an area within the home range), defense (e.g. damselfishes and European croakers) or prey defense (e.g. herrings , characins , catfishes , cods , squirrelfishes and porcupinefishes). Sound production is also used in mating (for attraction, arousal, approach or coordination) and communication between shoal mates. [Source: Nicholas White, Animal Diversity Web (ADW) /=]

In 2010, University of Auckland marine scientist Shahriman Ghazalin said that his research revealed that fish can "talk" to each other with noises including grunts, chirps and pops."All fish can hear, but not all can make sound — pops and other sounds made by vibrating their swim bladder, a muscle they can contract," Ghazali told the New Zealand Herald. [Source: AFP, July 7, 2010]

AFP reported: The gurnard species has a wide vocal repertoire and keeps up a constant chatter, Ghazali found after studying different species of fish placed into tanks.On the other hand, cod usually kept silent, except when they were spawning. "The hyopothesis is that they are using sound as a synchronisation so that the male and female release their eggs at the same time for fertilisation," he said. Some reef fish, such as the damselfish, made sounds to attempt to scare off threatening fish and even divers, he said. But anyone hoping to strike up a conversation with their pet goldfish is out of luck. "Goldfish have excellent hearing, but excellent hearing doesn't associate with vocalisation — they don't make any sound whatsoever," Ghazali said. He was to present his findings to the New Zealand Marine Sciences Society conference on Wednesday.

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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