1. Hearing.
a. Bony fishes have an inner ear for equilibrium, detecting acceleration, and hearing.
b. There is no external opening to the ear. A f ish's soft body tissue has about the same acoustic density as water; sound waves travel through soft tissue to the ear.
c. 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 a peak sensitivity near 20 Hz-probably typical for most bony fish species that lack the adaptations described below (Popper and Fay, 1980).
d. Some bony fish species have adaptations for enhanced sound reception at higher frequencies.
(1) In some fishes, the swim bladder lies against the ear and acts as an amplifier to enhance sound detection. See section Vill G for more information on the swim bladder.
(2) In some species, such as goldfish (Carassius auratus), a series of small bones connects the swim bladder to the inner ear. The hearing range of the goldfish is about 5 to 2,000 Hz, with a peak sensitivity near 400 Hz (Popper and Fay, 1980).
e. The adaptive significance of hearing in fishes is not well understood, but most bony fish species probably use hearing to detect prey.
f. In bony fishes, frequency range of sound production does not appear to be correlated with hearing sensitivity (Popper and Fay, 1980).
g. Sound in water travels more than four times the speed of sound in air.
2. Lateral line.
a. Like the ear, the lateral line senses vibrations. It functions mainly in distance perception and detecting low-frequency vibrations and directional water flow.
b. The lateral line system consists of a series of fluid-filled canals just below the skin of the head and along the sides of a bony fish's body. The canal is open to the surrounding water through tiny pores.
The lateral line consists of a series of fluid-filled canals just below the skin of the head and along the sides of a fish's body.
c. The lateral line canals contain a number of 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. This stimulation triggers a nerve impulse to the brain.
1. The eyesight in some species of bony fishes may be well developed. Goldfish (Carassius auratus) have excellent visual acuity up to 4.8 m (1 5 ft.) away (Bond, 1979).
2. Bony fishes have a basic vertebrate eye, with various structural adaptations.
a. The water's surface can reflect up to 80% of light that strikes it. Bony fishes have large lenses that help retain a large portion of the light entering the eye. In some species, the eye has a reflecting layer called the tapetum lucidum behind the retina. The tapetum lucidum helps reflect light back through the retina a second time.
b. The mudskipper (family Periophthalmidae) and several other species of bony fishes have accurate eyesight both above and below the surface of the water.
c. Some species have eyes positioned for a wider field of vision below or above their bodies. The South American catfish (family Hypophthalmidae) has eyes directed downward. Many species, including the sand divers (family Dactyloscopidae) have eyes directed toward the surface.
d. Due to its hourglass-shaped pupils, four-eyed fishes (family Anablepidae) can focus on images above and below the water simultaneously (Lagler, 1962). The half of the pupil above the waterline focuses on images above the water, while the half of the pupil below the waterline focuses on images under water.
The four-eyed fish (family Anablepidae) has hourglass-shaped pupils that lie at the waterline. They can focus on images above and below the water at the same time.
3 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 (Typhlogobius caiifomiensis) is born with eyes that degenerate as the goby matures.
4. Visual cells of bony fishes include rods and cones. Certain visual cells are specialized to particular wavelengths and intensities. Bony fishes, especially those that live in shallow-water habitats, probably have color vision.
1. Bony fishes have taste buds inside their mouths. Some species have taste buds along the head and ventral side of the body.
2. Taste perception hasn't been extensively studied in bony fishes. Some species can detect some sensations, such as salty, sweet, bitter, and acid stimuli (Lagler, 1962).
3. Taste may be responsible for the final acceptance or rejection of prey items.
1. Olfactory cells in the nasal sac detect tiny amounts of chemicals in solution.
2. The nasal areas and proficiency of the sense of smell vary among species. In general, the sense of smell is well developed in fishes.
a. 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 (Lagler, 1962).
b. Studies suggest that species of salmons (family Salmonidae) use smell to guide them to their home streams during the breeding season (Lagler, 1962).
c. Many bony fish species use the sense of smell to 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.
1. Some bony fishes in the families Electrophoridae, Gymnotidae, and Mormyridae produce a low-voltage electric current that sets up a field around the fish. 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.
Skin organs on the electric eel (Electrophorus electricus) detect disruptions in the electric field.
2. Tiny skin organs on the fish detect disruptions in the electric field that are caused by prey or inanimate objects. Thus, electroreception is an adaptation for detecting prey and for navigating in murky water.
3. Other fishes produce stronger electric currents for stunning prey.
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