How do fish communicate?

Fish, as far as I know ( of course there may be exceptions) , don't have any vocal organ… but they are proven to be social… so how do they manage to communicate with each other… on land, organisms like the honey-bee have their "tail-wagging dance"; ants have pheromones… so, what about fish?

Be glad to answer your questions. fish also sounds. The difference is that they are put in different positions by the body to sound.The sound of fish is about 20HZ. Difficult to discern the human ear. But you can rely on instruments to imitate and perceived. Of course, some fish also relies purely on action to exchange summarize a sound.Some fish by ultrasonic communication with dolphins is very similar (dolphins are not fish).

2 colors. Some fish by changing the body color transfer information, are located in the tropical shallow water.

3 flow. Some fish to pass through the water with their fins flapping shaped courtship information.

4 pheromone. Release pheromone few fish, mostly deep-sea fish.。

Sensory systems in fish

Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's (see vision in fishes). Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey. [1] Sharks can sense frequencies in the range of 25 to 50 Hz through their lateral line. [2]

Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish behavior in mazes reveals that they possess spatial memory and visual discrimination. [3]

Active Electroreception: Vertebrates


Electroreception, that is, the detection of naturally occurring electric stimuli by animals with specialized electroreceptors in their skin, can be found only in animals that live in water and thus is always coupled to an aquatic medium. Many marine and freshwater fishes, with the important exception of most (but not all) teleosts, are electroreceptive. Most electroreceptive animals detect weak electric fields, which originate in the biotic or abiotic environment and stimulate their ampullary electroreceptors organs, a process called passive electrolocation. In contrast, animals that use active electrolocation actively emit electric signals and perceive them after they have been modified by the external world. In this case, objects are detected because they change the self-emitted signal in a way perceivable by the animal.

Active electrolocation is only used by weakly electric fishes that produce electric signals with specialized organs ( electric organ discharges (EODs) ) and perceive them with epidermal electroreceptor organs . This combination can be found only in the South American gymnotiforms (or Knifefishes) and the African mormyriforms (mormyrids). Despite its surprising similarity at several levels, the ability to actively electrolocate has evolved independently in South America and Africa.

While an EOD is emitted, an electrical field builds up around the fish in the water ( Figure 1 ). For example, the field produced by the basically biphasic EOD of the mormyrid Gnathonemus petersii is an asymmetric dipole field with one smaller pole at the fish’s tail and the other pole constituting the entire body of the fish anterior to the electric organ. Because water is a conducting medium, alternating electric current flows through the water and enters (or leaves) the fish’s body mainly through the pores of the electroreceptor organs. The electroreceptor cells measure the electrical current flowing through them, which is proportional to the local electrical voltage between the inside and the outside of the fish.

Figure 1 . Schematic two-dimensional drawings of the electric fields of G. petersii distorted ventrally by a water plant (good conductor, left) or a stone (isolator, right). The fish is viewed from the side. Electrical field lines are drawn as thin lines. Modified after von der Emde G (1999) Active electrolocation of objects in weakly electric fish. Journal of Experimental Biology 202: 1205–1215.

If the fish approaches an object with electric properties different from those of the surrounding water, the electric field is distorted. The three-dimensional field distortions lead to a change in the voltage pattern within the ‘electric image’ which the object casts onto the fish’s skin surface. Thus, the electric image is defined as the local modulation of the electric field at an area on the skin. In mormyrids, a typical electric image has a center-surround (‘Mexican hat’) spatial profile. For example, a good conductor (e.g., a water plant, another fish, or a metal object) produces an image with a large center region where the local EOD amplitude increases, surrounded by a small rim area where the amplitude decreases. The image of a nonconductor such as a stone (or a plastic object) has an opposite appearance: in its center, local EOD amplitude decreases while it slightly increases in the surrounding rim area ( Figure 2 ). In order to gain information about objects during active electrolocation, the fish has to scan the electric image with its electroreceptors, which are innervated by primary sensory afferent nerve fibers that project to the brain.

Figure 2 . Electric images of a metal (left) or a plastic (right) object placed near the side of a G. petersii. The images on the fish’s skin are color coded with local amplitude-increases depicted in red and amplitude-decreases shown in blue. Above each graph, a single one-dimensional transect through the image is shown, which plots the local EOD amplitude change versus horizontal location along the midline of the fish. Note that both objects project Mexican-hat like images, however, of an inverted sign.

The Electric Organ Discharge

Electric fishes produce electric impulses by a muscle or nerve-cell-derived electric organs, which in the case of mormyrids lies in the caudal peduncle. In both Africa and South America, two basic types of EOD can be found: pulse-type EOD, where the interval between two EOD is clearly longer than the duration of a single EOD, and wave-type EOD, where discharges are produced one after another resulting in a quasisinusoidal wave signal ( Figure 3 ).

Figure 3 . Electric organ discharges (EOD) emitted by a pulse fish (G. petersii) from Africa (left) and a wavefish (Eigenmannia) from South America. Note the different time scales. G. petersii emits single and brief pulses with long and variable pauses in between, while Eigenmannia emits a continuous sinusoidal signal.

In all cases, EOD are used for nocturnal orientation through active electrolocation and for electrocommunication . For both processes, EOD waveform plays a critical role. The waveform of an EOD depends on the morphology of the electric organ and on the hormonal state of the animal. The electroreceptor organs involved in electrolocation are tuned to the characteristics of the self-produced EOD and thus can detect object-induced modifications of the local EOD. Most objects in the environment of the fishes are mainly resistive, but animate objects also have capacitive properties, which lead to waveform shifts of the local EOD in addition to amplitude changes. By detecting these waveform changes, weakly electric mormyrids can detect and identify capacitive objects.

The Environment of Weakly Electric Fishes

Weakly electric fishes live in freshwater habitats of Africa and South America. The about 200 different species of Mormyrids and the more than 150 species of Knifefishes have conquered many diverse habitats from small creeks to smaller and larger rivers and lakes. Most of these waters have a rather low electrical conductivity and a temperature well above 20 °C. In waters of cooler or more arid areas, the number of electric fish species greatly diminishes. G. petersii, for example, lives in rivers and stream of the rain forests of central Africa. During the day, the animals hide in the vegetation or in cavities at the bank of the rivers. During the night, they become active, leave their hiding places and search for food at the ground of the river.

Different species of weakly electric fishes feed on a variety of food. Apparently most, if not all species are predators and insect larvae, such as chironomid larvae, constitute a high percentage of their diet, even for larger species. However, there are also fish predators, such as the mormyrids Mormyrops anguilloides, which grows up to a length of about 100 cm. In Lake Tanganyika, this species hunts in groups for sleeping cichlids at night, a behavior which is called ‘pack hunting.’ The great majority of weakly electric fishes are strictly nocturnal and in the absence of light, the major sense used for prey detection is the electric sense, in particular active electrolocation.

  • Some flatfish use camouflage to hide themselves on the ocean floor.
  • Tuna can swim at speeds of up to 70 kph (43 mph).
  • A study has concluded that fish cannot feel pain. The part of the brain we use to feel pain does not exist in fish.
  • Most fish do not have eyelids. This is one reason why some species seek shade. Studies have shown that certain fish will use the shade cast from a single blade of grass to cover their eyes. One exception are sharks, who do have eyelids. If a shark gives you a wink, that might just be a sign to exit the water!
  • Although fish live in water, they can still drown. A fish’s gills extract oxygen from the hydrogen in water molecules, balancing the two components. When a fish is removed from its element and exposed only to air, its gills are unable to control this delicate balance. It inhales a lethal overdose of oxygen essentially killing the fish by “drowning”.
  • Some fish can actually fly! They are pelagic fish found in tropic seas. Although they fly, they do not actually flap their "wings" (enlarged pectoral fins). The fins are extended once the fish is in the air and used to help it glide greater distances, the average being up to several hundred feet. Flying fish typically travel a metre or so above the water and remain in the air for 5 to 10 seconds.
  • A Dwarf Pygmy Goby is the smallest! member of the fish family
  • A whale shark is the largest!
  • A clownfish
  • Some fish are beautiful
  • Others, like the catfish, are not so beautiful!
  • A seahorse is a fish!
  • Some people keep beautiful tropical fish as pets
  • A bear fishing for wild salmon
  • A shoal of fish
  • Koi carp are kept in garden ponds
  • Schooling, swimming together in large numbers, helps keep fish safe from predators
  • Can you spot the fish's gills?
  • Fish scales shining in the light


The word for fish in English and the other Germanic languages (German fisch Gothic fisks) is inherited from Proto-Germanic, and is related to the Latin piscis and Old Irish īasc, though the exact root is unknown some authorities reconstruct an Proto-Indo-European root *peysk-, attested only in Italic, Celtic, and Germanic. [8] [9] [10] [11]

The English word once had a much broader usage than its current biological meaning. Names such as starfish, jellyfish, shellfish and cuttlefish attest to almost any fully aquatic animal (including whales) once being 'fish'. "Correcting" such names (e.g. to 'sea star') is an attempt to retroactively apply the current meaning of 'fish' to words that were coined when it had a different meaning.

Fish, as vertebrata, developed as sister of the tunicata. As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium.

Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms. Jawless fish lineages are mostly extinct. An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils. They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth. The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors.

Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may have kept the larval form into adulthood (as some sea squirts do today), although perhaps the reverse is the case.


Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. For this reason, groups such as the class Pisces seen in older reference works are no longer used in formal classifications.

Traditional classification divides fish into three extant classes, and with extinct forms sometimes classified within the tree, sometimes as their own classes: [13] [14]

  • Class Agnatha (jawless fish)
    • Subclass Cyclostomata (hagfish and lampreys)
    • Subclass Ostracodermi (armoured jawless fish) †
    • Subclass Elasmobranchii (sharks and rays)
    • Subclass Holocephali (chimaeras and extinct relatives)
    • Subclass Actinopterygii (ray finned fishes)
    • Subclass Sarcopterygii (fleshy finned fishes, ancestors of tetrapods)

    The above scheme is the one most commonly encountered in non-specialist and general works. Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups:

    • Class Myxini (hagfish)
    • Class Pteraspidomorphi † (early jawless fish)
    • Class Thelodonti †
    • Class Anaspida †
    • Class Petromyzontida or Hyperoartia
      • Petromyzontidae (lampreys)
      • (unranked) Galeaspida †
      • (unranked) Pituriaspida †
      • (unranked) Osteostraci †
      • Class Placodermi † (armoured fish)
      • Class Chondrichthyes (cartilaginous fish)
      • Class Acanthodii † (spiny sharks)
      • Superclass Osteichthyes (bony fish)
        • Class Actinopterygii (ray-finned fish)
          • Subclass Chondrostei
            • Order Acipenseriformes (sturgeons and paddlefishes)
            • Order Polypteriformes (reedfishes and bichirs).
            • Infraclass Holostei (gars and bowfins)
            • Infraclass Teleostei (many orders of common fish)
            • Subclass Actinistia (coelacanths)
            • Subclass Dipnoi (lungfish, sister group to the tetrapods)

            † – indicates extinct taxon
            Some palaeontologists contend that because Conodonta are chordates, they are primitive fish. For a fuller treatment of this taxonomy, see the vertebrate article.

            The position of hagfish in the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, the Cyclostomata, that is a sister group of the Gnathostomata. [15] [16]

            The various fish groups account for more than half of vertebrate species. As of 2006, [17] there are almost 28,000 known extant species, of which almost 27,000 are bony fish, with 970 sharks, rays, and chimeras and about 108 hagfish and lampreys. A third of these species fall within the nine largest families from largest to smallest, these families are Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae, and Scorpaenidae. About 64 families are monotypic, containing only one species. The final total of extant species may grow to exceed 32,500. [18] Each year, new species are discovered and scientifically described. As of 2016, [19] there are over 32'000 documented species of bony fish and over 1'100 species of cartilaginous fish. Species are lost through extinction (see biodiversity crisis). Recent examples are the Chinese paddlefish or the smooth handfish.


            The term "fish" most precisely describes any non-tetrapod craniate (i.e. an animal with a skull and in most cases a backbone) that has gills throughout life and whose limbs, if any, are in the shape of fins. [21] Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic collection of taxa, including hagfishes, lampreys, sharks and rays, ray-finned fish, coelacanths, and lungfish. [22] [23] Indeed, lungfish and coelacanths are closer relatives of tetrapods (such as mammals, birds, amphibians, etc.) than of other fish such as ray-finned fish or sharks, so the last common ancestor of all fish is also an ancestor to tetrapods. As paraphyletic groups are no longer recognised in modern systematic biology, the use of the term "fish" as a biological group must be avoided.

            Many types of aquatic animals commonly referred to as "fish" are not fish in the sense given above examples include shellfish, cuttlefish, starfish, crayfish and jellyfish. In earlier times, even biologists did not make a distinction – sixteenth century natural historians classified also seals, whales, amphibians, crocodiles, even hippopotamuses, as well as a host of aquatic invertebrates, as fish. [24] However, according to the definition above, all mammals, including cetaceans like whales and dolphins, are not fish. In some contexts, especially in aquaculture, the true fish are referred to as finfish (or fin fish) to distinguish them from these other animals.

            A typical fish is ectothermic, has a streamlined body for rapid swimming, extracts oxygen from water using gills or uses an accessory breathing organ to breathe atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin, has jaws, has skin that is usually covered with scales, and lays eggs.

            Each criterion has exceptions. Tuna, swordfish, and some species of sharks show some warm-blooded adaptations – they can heat their bodies significantly above ambient water temperature. [22] Streamlining and swimming performance varies from fish such as tuna, salmon, and jacks that can cover 10–20 body-lengths per second to species such as eels and rays that swim no more than 0.5 body-lengths per second. [25] Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach. [26] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil lungfish and coelacanths), ganoid (various fossil fish but also living gars and bichirs), cycloid, and ctenoid (these last two are found on most bony fish). [27] There are even fish that live mostly on land or lay their eggs on land near water. [28] Mudskippers feed and interact with one another on mudflats and go underwater to hide in their burrows. [29] A single, undescribed species of Phreatobius, has been called a true "land fish" as this worm-like catfish strictly lives among waterlogged leaf litter. [30] [31] Many species live in underground lakes, underground rivers or aquifers and are popularly known as cavefish. [32]

            Fish range in size from the huge 16-metre (52 ft) whale shark to the tiny 8-millimetre (0.3 in) stout infantfish.

            Fish species diversity is roughly divided equally between marine (oceanic) and freshwater ecosystems. Coral reefs in the Indo-Pacific constitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in large river basins of tropical rainforests, especially the Amazon, Congo, and Mekong basins. More than 5,600 fish species inhabit Neotropical freshwaters alone, such that Neotropical fishes represent about 10% of all vertebrate species on the Earth. Exceptionally rich sites in the Amazon basin, such as Cantão State Park, can contain more freshwater fish species than occur in all of Europe. [33]

            The deepest living fish in the ocean so far found is the Mariana snailfish (Pseudoliparis swirei) which lives at deeps of 8,000 meters (26,200 feet) along the Mariana Trench near Guam. [34]

            The diversity of living fish (finfish) is unevenly distributed among the various groups, with teleosts making up the bulk of living fishes (96%), and over 50% of all vertebrate species. [19] The following cladogram [35] shows the evolutionary relationships of living fishes with their diversity. [19]


            Sponges are only just classed as animals. They have cells that are independent of each other but work together in a colony. It is possible for one single sponge cell to survive, reproduce and create a whole new sponge colony. They are so simple that they do not have any tissue or organs but they do have specialised cells that perform specific functions such as protection, generating a current of water and breaking down pathogens. Sponges are thought to be one of the first animals to have evolved and belong to a phylum of animals known as Porifera.

            Where are sponges found?

            Almost all sponges are found in marine environments. They live in both shallow coastal water and deep sea environments but they always live attached to the sea floor. Deep sea carnivorous sponges have been found more than 8000 m deep.

            How do sponges reproduce?

            Sponges can reproduce in a variety of ways, both asexually and sexually. Asexual methods of reproduction include: the growth of stolons that develop into new individuals a bud separating from the parent sponge and creating a new sponge elsewhere and the simple act of parts of a sponge breaking of and establishing in a new location.

            Sexual reproduction is performed by the fusion of a sperm and an egg. Sperm are released into the water column and enter another sponge before fertilizing an egg. The egg develops inside the sponge until being released as a larva. The larvae are able to move through the water and settle once they find a suitable substrate to grow into an adult sponge.

            How do sponges feed?

            Specific cells within the sponge have what are known as ‘flagella’. The flagella are used to create a flow of water within the interior of the sponge and that flows out large holes known as the ‘osculum’. The flow of water out of the osculum creates a vacuum that sucks water in through the pores of the sponge. As the water flows through the pores, the sponges filters out small organic matter, bacteria, phytoplankton and protozoans from the water. Some deep sea sponges have evolved carnivorous feeding strategies and trap small crustaceans using hook shaped structures.

            Interesting facts:

            • A gathering of different sponge species is known as a ‘sleeze’.
            • Sponges can filter out as much as 90% of all bacteria that passes through their pores – making them hugely important for disease prevention.
            • Many sponges have anti-cancerous properties and have been used to develop various cancer treatments

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            Bioluminescence In Jellyfish

            Bioluminescence, the ability to produce light, is a common feature among many marine animals, and is well represented in jellyfish. Jellies are free- swimming organisms that belong to the phylum Cnidaria, consisting of many different species, and the term also loosely encompasses the phylum Ctenophora, the comb jellies. Many jellyfish have the ability to bioluminescence, especially comb jellies, where more than 90% of planktonic species are known to produce light (Haddock and Case 1995). Arguably, the most famous of all bioluminescent invertebrates is the Aequorea victoria, which is the first species from which GFP was isolated, a discovery which went on to win the Nobel prize. Bioluminescence is used predominantly as a form of communication between animals, and can be used for defense, offense, and intraspecific communication. Many animals use bioluminescence in multiple ways, though jellyfish use it primarily for defense. It is important to note, however, that the different ways in which jellyfish use bioluminescence are still being discovered. This chart illustrates the many different ways in which marine mammals, including jellyfish, use bioluminescence.

            Schematic Diagram displaying the methods in which many marine animals use bioluminescence. Haddock. et al 2010

            Innate Behaviors: Movement and Migration

            Innate or instinctual behaviors rely on response to stimuli. The simplest example of this is a reflex action, an involuntary and rapid response to stimulus. To test the “knee-jerk” reflex, a doctor taps the patellar tendon below the kneecap with a rubber hammer. The stimulation of the nerves there leads to the reflex of extending the leg at the knee. This is similar to the reaction of someone who touches a hot stove and instinctually pulls his or her hand away. Even humans, with our great capacity to learn, still exhibit a variety of innate behaviors.

            Kinesis and Taxis

            Another activity or movement of innate behavior is kinesis, or the undirected movement in response to a stimulus. Orthokinesis is the increased or decreased speed of movement of an organism in response to a stimulus. Woodlice, for example, increase their speed of movement when exposed to high or low temperatures. This movement, although random, increases the probability that the insect spends less time in the unfavorable environment. Another example is klinokinesis, an increase in turning behaviors. It is exhibited by bacteria such as E. coli which, in association with orthokinesis, helps the organisms randomly find a more hospitable environment.

            A similar, but more directed version of kinesis is taxis: the directed movement towards or away from a stimulus. This movement can be in response to light (phototaxis), chemical signals (chemotaxis), or gravity (geotaxis) and can be directed toward (positive) or away (negative) from the source of the stimulus. An example of a positive chemotaxis is exhibited by the unicellular protozoan Tetrahymena thermophila. This organism swims using its cilia, at times moving in a straight line, and at other times making turns. The attracting chemotactic agent alters the frequency of turning as the organism moves directly toward the source, following the increasing concentration gradient.

            Fixed Action Patterns

            A fixed action pattern is a series of movements elicited by a stimulus such that even when the stimulus is removed, the pattern goes on to completion. An example of such a behavior occurs in the three-spined stickleback, a small freshwater fish (Figure 1). Males of this species develop a red belly during breeding season and show instinctual aggressiveness to other males during this time. In laboratory experiments, researchers exposed such fish to objects that in no way resemble a fish in their shape, but which were painted red on their lower halves. The male sticklebacks responded aggressively to the objects just as if they were real male sticklebacks.

            Figure 1. Male three-spined stickleback fish exhibit a fixed action pattern. During mating season, the males, which develop a bright red belly, react strongly to red-bottomed objects that in no way resemble fish.


            Figure 2. Wildebeests migrate in a clockwise fashion over 1800 miles each year in search of rain-ripened grass. (credit: Eric Inafuku)

            Migration is the long-range seasonal movement of animals. It is an evolved, adapted response to variation in resource availability, and it is a common phenomenon found in all major groups of animals. Birds fly south for the winter to get to warmer climates with sufficient food, and salmon migrate to their spawning grounds. The popular 2005 documentary March of the Penguins followed the 62-mile migration of emperor penguins through Antarctica to bring food back to their breeding site and to their young. Wildebeests (Figure 2) migrate over 1800 miles each year in search of new grasslands.

            Although migration is thought of as innate behavior, only some migrating species always migrate (obligate migration). Animals that exhibit facultative migration can choose to migrate or not. Additionally, in some animals, only a portion of the population migrates, whereas the rest does not migrate (incomplete migration). For example, owls that live in the tundra may migrate in years when their food source, small rodents, is relatively scarce, but not migrate during the years when rodents are plentiful.


            Figure 3. The painted stork uses its long beak to forage. (credit: J.M. Garg)

            Foraging is the act of searching for and exploiting food resources. Feeding behaviors that maximize energy gain and minimize energy expenditure are called optimal foraging behaviors, and these are favored by natural section. The painted stork, for example, uses its long beak to search the bottom of a freshwater marshland for crabs and other food (Figure 3).

            Neural coding in electric fish

            Bruce Carlson and his colleagues from Washington University in St Louis, USA, explain that electric fish not only convey information about themselves in the structure of each electric pulse but also vary the duration of the interval between pulses to communicate their behavioural state, such as whether they are subordinate or dominant and how aggressive they are (p. 2365 ). All sensory information is encoded by neurons into patterns of electrical spikes. In the case of electric signal perception by mormyrids, information is encoded by specialised receptors known as knollenorgans into both spike timing differences between receptors and interspike intervals within receptors. Carlson and his colleagues also describe how two subfamilies of pulse-type African mormyrids differ in their ability to distinguish differences in the waveform of emitted electric signals and they explain that these perceptual differences are due to differences in midbrain structures, as well as differences in the distribution of the knollenorgan receptors on the fish's bodies. The authors conclude by saying, ‘The mormyrid electric communication pathway is a powerful model for integrating mechanistic studies of temporal coding with evolutionary studies of correlated differences in brain and behaviour to investigate neural mechanisms for processing temporal codes.’

            Continuing the theme of pulse-type weakly electric fish, Javier Nogueira and Angel Caputi from Montevideo, Uruguay, address the fundamental question of the properties of a neuron and how they enable that neuron to participate in a particular circuit. In this review, they focus on one specific cell type: spherical neurons in the electrosensory lobe of Gymnotus omarorum (p. 2380 ). Having defined the properties of this type of neuron – which is a one-spike-onset neuron – Nogueira and Caputi go on to explain that the cell plays a key role in distinguishing between electric fields that have been self-generated and externally generated. Spherical neurons allow the fish to preferentially process self-generated electric images of their surroundings in the presence of weaker electric fields generated by surrounding fish of their own species. Comparing the function of one-spike-onset neurons in the fish's electrosensory system

            Concluding the section on information encoded in electric fish fields and how the animals process that information, Maurice Chacron, Sarah Stamper and Eric Fortune describe an additional source of information exploited by a second category of gymnotiform fish, which emits a continuous – wave-type – electric field (p. 2393 ). Chacron, from McGill University, and colleagues explain that low frequency electrical signals produced by social interactions between these fish add an additional frequency component to the electric field that results in a low frequency envelope that modulates the structure of the electric field. The envelopes produced by the movement of a fish's body have lower frequency properties than envelopes produced by the interaction between close together fish, and the trio adds that congregating fish, ‘respond in robust and stereotypical ways to social envelopes that serve to increase the envelope frequency’. Moving on to consider how the fish extract information from electric field envelopes, the team traces the processing circuit from the response of the electroreceptors that detect electric fields, through to a region of the brain called the torus semicircularis, where the signal is extracted, leading to perception and behaviour.

            Critter Catalog

            Physical description varies widely with sex, age, and habitat. In general, they are streamlined, with 8 to 12 spines in the anal fin and lack teeth at the base of the tongue (unlike their close relatives, Oncorhynchus clarkii). The undersides tend to be silvery with a pinkish red stripe along the upper-middle part of the body, though this stripe can vary from dark to light. Resident rainbows and spawning steelhead tend to be lighter with more pronounced pink stripes, while ocean-going steelhead are darker and silvery to blend into their ocean environment. Most have black spots above the lateral line, and resident rainbows tend to have more intense spotting, well below the lateral line. Juvenile fish have 8 to 13 parr marks on their sides and become silvery as they mature. (Delaney, 2005 Gall and Crandell, 1992 Klontz, 1991 Van Hulle, 2005)

            • Other Physical Features
            • ectothermic
            • heterothermic
            • bilateral symmetry
            • polymorphic
            • Sexual Dimorphism
            • male larger
            • Range mass 25.4 (high) kg 55.95 (high) lb
            • Average mass 4 kg 8.81 lb
            • Range length 120 (high) cm 47.24 (high) in
            • Range basal metabolic rate 0.6 to 75 cm3.O2/g/hr
            • Average basal metabolic rate 55 cm3.O2/g/hr

            Where do they live?

            Oncorhynchus mykiss are only native to the Pacific Coast of North America, extending from Alaska down to the border between California and Mexico. However, they have been introduced throughout the United States. and in every continent except for Antarctica for game fishing purposes. There are two forms: freshwater resident and anadromous. The resident form is commonly called rainbow trout while the anadromous form is called steelhead. (Delaney, 2005 "Oregon Coast Steelhead Evolutionary Significant Unit", 1998)

            • Biogeographic Regions
            • nearctic
              • introduced
              • native
              • introduced
              • introduced
              • introduced
              • introduced
              • introduced
              • Other Geographic Terms
              • cosmopolitan

              What kind of habitat do they need?

              Freshwater, brackish, or marine waters of temperate zones. The anadromous form, called steelhead, spawn and complete their early development in freshwater mountain streams, then migrate to spend their adult life in the ocean. In freshwater, they prefer cool water but have been known to tolerate water temperatures up to 24°C (native climates have water temperatures around 12°C in the summer). Productive streams have a good mixture of riffles and pools and overhanging vegetation for shade. Most importantly, they require gravel beds to lay their eggs, and therefore, are sensitive to sedimentation and channel scouring. Juvenile trout prefer protective cover and low velocity water and have been known to be swept away and killed in water that is too fast. Since they are native to the western U.S., then tend to be found in coastal streams and rivers which naturally have reduced flow in summer months. (Behnke, 1992 Gall and Crandell, 1992 "Life History Notes: Rainbow Trout", 2005)

              • These animals are found in the following types of habitat
              • temperate
              • tropical
              • saltwater or marine
              • freshwater
              • Aquatic Biomes
              • pelagic
              • lakes and ponds
              • rivers and streams
              • temporary pools
              • coastal
              • brackish water
              • Range elevation 0 to 3000 m 0.00 to 9842.52 ft
              • Range depth 10 to 200 m 32.81 to 656.17 ft

              How do they grow?

              Oncorhynchus mykiss larvae go through a series of morphological changes to prepare for life in the sea, and spend their adult life there for 2 to 3 years before migrating upstream to spawn in their natal stream. ("The Life Histories of the Steelhead Rainbow Trout and Silver Salmon", 1954 Thrower, et al., 2004)

              How do they reproduce?

              Female fish find suitable nest sites while their male mate guards the site from other interested males and predators. The female digs the nest (called a redd) with her anal fin and then descends upon it to position her vent and anal fin into the deepest part of the redd. The male joins her in a parallel position so that their vents are opposite each other. The male and female open their mouths, arch their backs, and deposit the eggs and milt (fish sperm) at the same time. The eggs are enveloped in a cloud of milt and are fertilized. Only a few seconds elapse from the time the female drops into the redd and fertilization occurs. The female then covers the nest with gravel and repeats the process again a few times until she has deposited all of her eggs. ("The Life Histories of the Steelhead Rainbow Trout and Silver Salmon", 1954)

              Adult rainbow trout and steelhead lay their eggs in a series of nests in gravel. Collectively, the nests are called a redd. When they hatch, the hatchlings are still attached to, and survive on their yok sac. They remain in the protective gravel for about 2 to 3 weeks when they have shed their yolk sacs and are fit enough to survive in the open water. Juvenile fish tend to stick to shallow and side areas of the streams where there is protective cover and slow-moving currents. The remain in their native streams for 1 to 3 years while they grow fit enough to spawn or migrate to the ocean, in the case of steelheads. ("The Life Histories of the Steelhead Rainbow Trout and Silver Salmon", 1954 Behnke, 1992 Delaney, 2005 Thrower, et al., 2004)

              • Key Reproductive Features
              • iteroparous
              • seasonal breeding
              • sexual
              • fertilization
                • external
                • How often does reproduction occur? Rainbow trout breed every three to five years. Though steelhead are one of the only salmonids able to spawn twice in a lifetime, the return rate is very low, about 10-20%
                • Breeding season Spawning occurs from March to July, depending on temperature and other climatic variables. Winter steelhead in California start spawning as early as January.
                • Range number of offspring 200 to 8000
                • Average number of offspring 3500 AnAge
                • Range time to hatching 3 to 16 weeks
                • Range time to independence one to three years
                • Range age at sexual or reproductive maturity (female) 3 to 11 years
                • Range age at sexual or reproductive maturity (male) 3 to 11 years

                Female rainbow trout and steelehead simply lay their eggs in a gravel bed and leave the young hatchlings to mature on their own. Male steelhead frequently breed with multiple female partners, possibly because more females than males die during the breeding period. (Delaney, 2005)

                • Parental Investment
                • no parental involvement
                • pre-fertilization
                  • provisioning
                  • protecting
                    • female
                    • protecting
                      • female

                      How long do they live?

                      How do they behave?

                      Steelhead and rainbow trout are solitary fish, leaving the group of juveniles once they have hatched from eggs. As adults, they compete with all kinds of trout and salmon for food and habitat. The largest trout tend to get the best habitat. Adult steelhead have a remarkable homing instinct and consistently return to their natal stream to spawn. Steelhead have been known to migrate thousands of kilometers between the ocean and their natal stream to spawn. Migration ranges have been severely cut due to excessive damming of most western rivers and streams. ("The Life Histories of the Steelhead Rainbow Trout and Silver Salmon", 1954 Alexander, 1991 Behnke, 1992)

                      • Key Behaviors
                      • natatorial
                      • motile
                      • migratory
                      • solitary
                      • territorial
                      • dominance hierarchies
                      • Range territory size 10 to 5000 km^2

                      Home Range

                      Resident rainbow trout maintain small territories but also disperse from areas with higher population densities in order to find food. ("The Life Histories of the Steelhead Rainbow Trout and Silver Salmon", 1954 Behnke, 1992)

                      How do they communicate with each other?

                      There is little communication between rainbow trout and steelhead. Once the fry emerge from the gravel, they become hostile to each other and compete for habitat. Larger fish usually win out the best habitat and food sources, and there is a size hierarchy within aquatic systems among all trout species. Potential mates communicate before spawning with visual cues. Oncorhynchus mykiss individuals are visual predators, relying on a keen sense of vision to detect prey. Trout species use both chemical cues and detection of the earth's magnetic fields to navigate to and from natal streams and on ocean journeys. (Grubb, 2003)

                      • Communication Channels
                      • visual
                      • tactile
                      • Perception Channels
                      • visual
                      • tactile
                      • chemical
                      • magnetic

                      What do they eat?

                      Rainbow trout and steelhead are insectivorous and piscivorous. Resident rainbow trout tend to eat more fish than steelhead. Both species primarily feed on invertebrate larvae drifting in mid-water to conserve energy that would be expended if they were foraging for food in the substrate. Young rainbow trout and steelhead eat insect larvae, crustaceans, other aquatic invertebrates, and algae. (Behnke, 1992 Delaney, 2005 Klontz, 1991 "Steelhead: Oncorhynchus Mykiss", 2005 Smith, 1991 Van Hulle, 2005)

                      • Primary Diet
                      • carnivore
                        • insectivore
                        • Animal Foods
                        • fish
                        • insects
                        • aquatic or marine worms
                        • aquatic crustaceans
                        • Plant Foods
                        • algae

                        What eats them and how do they avoid being eaten?

                        In the Great Lakes, sea lampreys are the most common predators of all salmonid species, including rainbow trout. Other predators in both native and introduced habitats include: larger trout, fish-eating birds like great blue herons (Ardea herodias), mergansers (Mergus), and kingfishers (Ceryle), and mammals including mink (Neovison vison and Mustela lutreola), raccoons (Procyon lotor), river otters (Lontra), grizzly bears (Ursus arctos), American black bears (Ursus americanus), humans, and larger marine mammals who feed on migrating steelhead. Rainbow trout tend to stick to the sides of streams and rivers where shading is prevalent, the water is less swift, and protection is greatest. Trout species are vigilant and capable of rapid swimming to escape predation. ("Steelhead: Oncorhynchus Mykiss", 2005 Smith, 1991)

                        • Known Predators
                          • kingfishers (Ceryle)
                          • grizzly bears (Ursus arctos)
                          • American black bears (Ursus americanus)
                          • river otters (Lontra canadensis)
                          • mink (Neovison vison and Mustela lutreola)
                          • raccoons (Procyon lotor)
                          • sea lampreys (Petromyzon marinus)
                          • mergansers (Mergus merganser)
                          • great blue herons (Ardea herodias)
                          • other trout species (Salmonidae)
                          • humans ( Homo sapien )

                          What roles do they have in the ecosystem?

                          Rainbow trout and steelhead are important predators in their native habitats, they also serve as important sources of food for larger predators. (Smith, 1991)

                          Do they cause problems?

                          Rainbow trout have been introduced throughout the world, negatively impacting species of native freshwater fishes and, therefore, native fisheries.

                          How do they interact with us?

                          These fish are one of the most popular game fishes around the world, leading to nearly global introduction. They are introduced to stimulate local angling and associated recreational economies. However, where they are introduced, they can outcompete native trout species. ("Steelhead: Oncorhynchus Mykiss", 2005 "Oregon Coast Steelhead Evolutionary Significant Unit", 1998 "Life History Notes: Rainbow Trout", 2005)

                          Are they endangered?

                          Steelhead are endangered in Washington and California, and threatened in California, Oregon, Washington, and Idaho. Most of their decline has resulted from impacts to habitat and shrinking of spawning routes due to dams and other diversions. Siltation, caused by forestry practices, and erosion, caused by urban and agricultural development, has also impacted spawning beds. (Behnke, 1992 Delaney, 2005 "Oregon Coast Steelhead Evolutionary Significant Unit", 1998 Van Hulle, 2005)


                          Tanya Dewey (editor), Animal Diversity Web.

                          Katherine Ridolfi (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.


                          Ohio Department of Natural Resources, Division of Wildlife. 2005. "Life History Notes: Rainbow Trout" (On-line). Accessed October 09, 2005 at

                          NOAA Fisheries Office of Protected Resources. 1998. "Oregon Coast Steelhead Evolutionary Significant Unit" (On-line). Accessed October 09, 2005 at

                          Michigan Department of Natural Resources. 2005. "Steelhead: Oncorhynchus Mykiss" (On-line). Accessed October 07, 2005 at,1607,7-153-10364_18958-45692--,00.html.

                          California Department of Fish and Game. The Life Histories of the Steelhead Rainbow Trout and Silver Salmon. Bulletin No. 98. Sacramento, CA: California Department of Fish and Game. 1954. Accessed October 10, 2005 at

                          Alexander, G. 1991. Trout as Prey. Pp. 112-117 in J Schnell, J Stolz, eds. Trout: The Wildlife Series . Harrisburg, PA: Stackpole Books.

                          Behnke, R. 1992. Native Trout of Western North America . Bethesda, MD: American Fisheries Society.

                          Delaney, K. 2005. "Rainbow Trout: Wildlife Notebook Series" (On-line). Accessed October 09, 2005 at

                          Gall, G., P. Crandell. 1992. "Oncorhynchus mykiss Rainbow Trout" (On-line). Fishbase. Accessed October 07, 2005 at

                          Grubb, T. 2003. The Mind of the Trout: A Cognitive Ecology for Biologists and Anglers . Madison, WI: The University of Wisconsin Press.

                          Klontz, G. 1991. "UC Davis California Aquaculture" (On-line pdf). Manual for Rainbow Trout Production on the Family-Owned Farm. Accessed October 20, 2005 at

                          Smith, R. 1991. Rainbow Trout (Oncorhynchus mykiss). Pp. 304-323 in J Stoltz, J Schnell, eds. Trout: The Wildlife Series . Harrisburg, PA: Stackpole Books.

                          Thrower, F., J. Hard, J. Joyce. 2004. Genetic architecture of growth and early life-history transitions in anadromous and derived freshwater populations of steelhead. Journal of Fish Biology , 65: 286-307.

                          Van Hulle, F. 2005. "Steelhead Trout: Wildlife Notebook Series" (On-line). Accessed October 10, 2005 at

                          Ridolfi, K. 2006. "Oncorhynchus mykiss" (On-line), Animal Diversity Web. Accessed June 22, 2021 at

                          BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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