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The ears of a bony fish function in equilibrium, detecting acceleration, and hearing.
There are no external openings to the ears. Sound waves travel through soft tissue to the ears. (A fish's soft body tissue has about the same acoustic density as water).
There is great variation in hearing sensitivity, bandwidth, and upper frequency limit among bony fish species. The hearing range of the cod Gadus morhua is about 2 to 500 Hz, with peak sensitivity near 20 Hz - probably typical for most bony fish species that lack the adaptations described below.
In some bony fish species, the swim bladder is associated with adaptations for enhanced sound reception at higher frequencies. In some, the swim bladder lies against the ear and acts as an amplifier to enhance sound detection. In other species, such as goldfish (
), a series of small bones connects the swim bladder to the ear.
The hearing range of the goldfish is about 5 to 2,000 Hz - with peak sensitivity near 400 Hz.
Recently researchers have discovered that the American shad (Alosa sapidissima) and certain related species can detect sounds from 200 to 180,000 Hz. The researchers theorize that this ultrasonic hearing is an adaptation for avoiding echolocating dolphins, which typically produce clicks at about 100,000 Hz.
Like the ear, the lateral line senses vibrations. It functions mainly in detecting low-frequency vibrations and directional water flow, and in distance perception.
The lateral line system is a series of fluid-filled canals just below the skin of the head and along the sides of a bony fish's body. The canals are open to the surrounding water through tiny pores.
Lateral line canals contain sensory cells. Tiny hairlike structures on these cells project out into the canal. Water movement created by turbulence, currents, or vibrations displaces these hairlike projections and stimulates the sensory cells.
In bony fishes, frequency range of sound production does not appear to be correlated with hearing sensitivity.
Most species of bony fishes probably detect prey by sound.
In water, sound travels more than four times the speed of sound through air.
Bony fishes have a basic vertebrate eye, with various structural adaptations. A bony fish's eye includes rods and cones. Bony fishes, especially those that live in shallow-water habitats, probably have color vision. Certain visual cells are specialized to particular wavelengths and intensities.
In general, deep-water fishes have large eyes, allowing them to absorb as much light as possible in the dark. Shallow-water fishes generally have smaller eyes.
The pupils of some species of bony fishes, such as eels, contract and dilate depending on light conditions. In most species of bony fishes, however, pupils can't contract or dilate.
The water's surface can reflect up to 80% of light that strikes it. Bony fishes have large lenses to make the most of available light. In some species, the eye has a reflective layer called the tapetum lucidum behind the retina. The
reflects light back through the retina a second time.
The mudskipper (family Periophthalmidae) and several other species of bony fishes have excellent eyesight both above and below the surface of the water. The four-eyed fishes (family Anablepidae) swim at the water's surface. Their eyes lie at the water line and are adapted for seeing in air and in water. Separate retinae and an asymmetric lens allow these remarkable fish to focus on images above the water and on images under water simultaneously.
The eyesight in some species of bony fishes may be well developed. Goldfish (
) have excellent visual acuity up to 4.8 m (16 ft.) away.
Some species of bony fishes have no eyes. The blind cavefishes (family Amblyopsidae) have no vision perception. Other senses help them find prey. The blind goby (
) is born with eyes that degenerate as the goby matures.
Bony fishes have taste buds in their mouths. Some species have taste buds along the head and ventral side of the body.
Taste perception hasn't been extensively studied in bony fishes. Some species can detect some sensations, such as salty, sweet, bitter, and acid stimuli.
Taste may be responsible for the final acceptance or rejection of prey items.
Olfactory cells in the nasal sac detect tiny amounts of chemicals in solution.
In general, the sense of smell is well developed in fishes. The nasal areas and extent of the sense of smell vary among species.
Species of freshwater eels (family Anguillidae) may detect chemicals in extremely low dilutions. Eels may detect a substance when only three or four molecules have entered the nasal sac.
Studies suggest that smell guides at least some species of salmons (family Salmonidae) to their home streams during the breeding season.
Some species can detect pheromones, chemical substances released by an animal that influence the behavior of members of the same species. Fishes may release pheromones during the breeding season or when alarmed.
Some bony fishes in the families Electrophoridae, Gymnotidae, and Mormyridae produce a low-voltage electric current that sets up a field around the fish. Tiny skin organs on the fish detect disruptions in the electric field that are caused by prey or inanimate objects.
Electric organs are made up of cells called electrocytes that have evolved from muscle cells. Electrocytes typically are thin and stacked on top of one another.
Electroreception is an adaptation for detecting prey and for navigation in murky water.
Some other fishes produce stronger electric currents for stunning prey.