BIOLOGY OF FISHES
realise that the beautifully coloured parrotfishes, wrasses,
angelfishes, etc. are not likely to have evolved their intricately coloured patterns just for the appreciation of some
land animal. For most fishes, vision is important in finding
their food, as well as in avoiding their predators, but in
those species that have males and females with strikingly
different colour patterns (as in the sexually dimorphic parrotfishes, wrasses, etc.) colour vision must also be important in mate recognition.
The field of view is quite large for those fishes with eyes in
the usual position, on the sides of their head, and many
species can rotate their eyes independently like a chameleon. Periophthalmus, the mud skipper, is a goby that
spends most of its time out of the water climbing about the
roots of mangrove trees. It can see quite well in air, as anyone who has tried to catch one of these elusive little fishes
will attest. It has protruding periscope-like eyes, which it
can retract and roll around in the eye socket to moisten,
erecting them again to scan the area for predators or possible prey. With its movable eyes on top of its head, the mud
skipper has a 360 0 field of vision.
If a sole is blinded it loses the ability to blend with its surroundings, hence the light rays that enter the eyes are important to it.
Anglers know only too well that if you can see a fish, the
fish can see you, and the best catches are generally made
when the water is not too clear.
HEARING AND LATERAL-LINE SENSE
The density of water is about 1 000 times greater than
that of air; consequently, water is much less compressible
than air. These two features, greater density and resistance
to compression, greatly affect the production and transmission of sound. In air, sound travels relatively slowly as a
periodic form of compression waves. In water, sound
travels about five times faster and usually via particle displacements as well as compression waves. The particle
displacement form of sound energy is strongest at close
range to the sound source, hence termed the near-field
effect; whereas the compression waves extend farther
from the sound source and are thus known as the far-field
effect.
Fishes detect sounds with lateral-line receptors and their
ears. The sensory organs (termed "hair cells" or "neuromasts") of the lateral line and the ears are very similar in
structure. But the lateral-line neuromasts, being mechanoreceptors more-or-Iess directly exposed to the water surrounding the fish, are especially sensitive to the particle displacement (near-field) form of sound energy. Experiments
have confirmed that the lateral-line receptors are sensitive
only to low frequency sounds (10-200 Hz), which have a
8
greater near-field component. The swimming sounds produced by the motion of fishes or other animals through the
water are primarily of low frequency, and the lateral-line is
thus "well designed" (so to speak) to detect movements of
nearby animals. The lateral-line neuromasts are usually
found in small perforated tubes running just under the skin
of the head and/or along the midlateral part of the body
(hence "lateral line").
The ability to detect the motion of other animals is useful
to both predators and prey, and especially at night or in the
deep sea where sunlight may be nonexistent. The greatly
elongated lateral line of some midwater fishes (e.g.
trichiurids, trachipterids, Stylephorus and Radiicephalus)
is presumably very efficient at detecting any movements
in their vicinity. Although the lateral line is absent from the
body of most c1upeid fishes, the well-developed lateralis
canals of the head are important for the schooling behaviour of these fishes.
The ears of fishes are convoluted fluid-filled organs
(labyrinths) enclosed in bony chambers (otic capsules) on
either side of the skull. The upper part of each labyrinth
consists of three curved membranous tubes (semicircular
canals) that join a central chamber called the utriculus. Two
of the semicircular canals lie in vertical planes approximately at right angles to each other; the third canal is located in the horizontal plane. Movements of the head result
in displacements of the fluid (endolymph) in the semicircular canals and utriculus; these fluid displacements cause
deformation of the sensory hair cells on the inner wall
of the labyrinth. Stimulation of these hair cells will send
nervous impulses to the brain to be read as information
on the movement and orientation of the fish. Perception
of gravity appears to be primarily accomplished by the
utriculus.
The lower part of the labyrinth comprises two adjoining
chambers, the sacculus and lagena, each with a dense calcareous otolith ("ear bone"). The utriculus (which also contains an otolith) is usually joined to the sacculus, but in
some gobies the upper and lower parts of the labyrinth are
completely separate. The ears of fishes are sensitive to
sounds of a wide range in frequency, but the hair cells, being
located within the otic capsules of the skull, are primarily
sensitive to the compression wave (far-field) form of sound
energy. This pressure wave is either transmitted directly
through the tissues of the skull to the ear, or, in the case of
fishes with a connection between the swimbladder and the
ears, the sound wave induces vibrations of the gas-filled
swimbladder, and these vibrations are conveyed directly to
the ears. Fishes with a connection between the swimbladder
and the ears are especially sensitive to high-frequency
sounds (up to 7 kHz). At the labyrinth the sound wave
vibrations are transmitted to the endolymph and otoliths,
and the vibrations of the otoliths stimulate the hair cells
with which they are in contact.
realise that the beautifully coloured parrotfishes, wrasses,
angelfishes, etc. are not likely to have evolved their intricately coloured patterns just for the appreciation of some
land animal. For most fishes, vision is important in finding
their food, as well as in avoiding their predators, but in
those species that have males and females with strikingly
different colour patterns (as in the sexually dimorphic parrotfishes, wrasses, etc.) colour vision must also be important in mate recognition.
The field of view is quite large for those fishes with eyes in
the usual position, on the sides of their head, and many
species can rotate their eyes independently like a chameleon. Periophthalmus, the mud skipper, is a goby that
spends most of its time out of the water climbing about the
roots of mangrove trees. It can see quite well in air, as anyone who has tried to catch one of these elusive little fishes
will attest. It has protruding periscope-like eyes, which it
can retract and roll around in the eye socket to moisten,
erecting them again to scan the area for predators or possible prey. With its movable eyes on top of its head, the mud
skipper has a 360 0 field of vision.
If a sole is blinded it loses the ability to blend with its surroundings, hence the light rays that enter the eyes are important to it.
Anglers know only too well that if you can see a fish, the
fish can see you, and the best catches are generally made
when the water is not too clear.
HEARING AND LATERAL-LINE SENSE
The density of water is about 1 000 times greater than
that of air; consequently, water is much less compressible
than air. These two features, greater density and resistance
to compression, greatly affect the production and transmission of sound. In air, sound travels relatively slowly as a
periodic form of compression waves. In water, sound
travels about five times faster and usually via particle displacements as well as compression waves. The particle
displacement form of sound energy is strongest at close
range to the sound source, hence termed the near-field
effect; whereas the compression waves extend farther
from the sound source and are thus known as the far-field
effect.
Fishes detect sounds with lateral-line receptors and their
ears. The sensory organs (termed "hair cells" or "neuromasts") of the lateral line and the ears are very similar in
structure. But the lateral-line neuromasts, being mechanoreceptors more-or-Iess directly exposed to the water surrounding the fish, are especially sensitive to the particle displacement (near-field) form of sound energy. Experiments
have confirmed that the lateral-line receptors are sensitive
only to low frequency sounds (10-200 Hz), which have a
8
greater near-field component. The swimming sounds produced by the motion of fishes or other animals through the
water are primarily of low frequency, and the lateral-line is
thus "well designed" (so to speak) to detect movements of
nearby animals. The lateral-line neuromasts are usually
found in small perforated tubes running just under the skin
of the head and/or along the midlateral part of the body
(hence "lateral line").
The ability to detect the motion of other animals is useful
to both predators and prey, and especially at night or in the
deep sea where sunlight may be nonexistent. The greatly
elongated lateral line of some midwater fishes (e.g.
trichiurids, trachipterids, Stylephorus and Radiicephalus)
is presumably very efficient at detecting any movements
in their vicinity. Although the lateral line is absent from the
body of most c1upeid fishes, the well-developed lateralis
canals of the head are important for the schooling behaviour of these fishes.
The ears of fishes are convoluted fluid-filled organs
(labyrinths) enclosed in bony chambers (otic capsules) on
either side of the skull. The upper part of each labyrinth
consists of three curved membranous tubes (semicircular
canals) that join a central chamber called the utriculus. Two
of the semicircular canals lie in vertical planes approximately at right angles to each other; the third canal is located in the horizontal plane. Movements of the head result
in displacements of the fluid (endolymph) in the semicircular canals and utriculus; these fluid displacements cause
deformation of the sensory hair cells on the inner wall
of the labyrinth. Stimulation of these hair cells will send
nervous impulses to the brain to be read as information
on the movement and orientation of the fish. Perception
of gravity appears to be primarily accomplished by the
utriculus.
The lower part of the labyrinth comprises two adjoining
chambers, the sacculus and lagena, each with a dense calcareous otolith ("ear bone"). The utriculus (which also contains an otolith) is usually joined to the sacculus, but in
some gobies the upper and lower parts of the labyrinth are
completely separate. The ears of fishes are sensitive to
sounds of a wide range in frequency, but the hair cells, being
located within the otic capsules of the skull, are primarily
sensitive to the compression wave (far-field) form of sound
energy. This pressure wave is either transmitted directly
through the tissues of the skull to the ear, or, in the case of
fishes with a connection between the swimbladder and the
ears, the sound wave induces vibrations of the gas-filled
swimbladder, and these vibrations are conveyed directly to
the ears. Fishes with a connection between the swimbladder
and the ears are especially sensitive to high-frequency
sounds (up to 7 kHz). At the labyrinth the sound wave
vibrations are transmitted to the endolymph and otoliths,
and the vibrations of the otoliths stimulate the hair cells
with which they are in contact.