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Bony Fishes

Bony Fishes
Class - Osteichthyes
Scientific ClassificationClass Osteichthyes
Class Osteichthyes includes all bony fishes.
 Like all fishes, Osteichthyes are cold-blooded
vertebrates that breathe through gills and use
fins for swimming.
 Bony fishes share several distinguishing
features: a skeleton of bone, scales, paired fins,
one pair of gill openings, jaws, and paired
Scientific ClassificationClass Osteichthyes
Osteichthyes includes the largest number of
living species of all scientific classes of
vertebrates, more than 28,000 species.
Osteichthyes account for about 96% of all
fish species. Fishes not included in the
Osteichthyes are the Chondrichthyes
(sharks and their relatives), the Myxini
(hagfishes), and the Cephalaspidomorphi
Living Osteichthyes are divided into three
subclasses: Dipnoi, Crossopterygii, and
The subclass Dipnoi (lungfishes) is characterized by
an upper jaw fused to the braincase, fused teeth, and
the presence of an air-breathing organ that opens to
the esophagus. A lungfish's caudal fin is continuous
with its dorsal and anal fins. Its pelvic and pectoral fins
are long and tubular.
Subclasses- Crossopteryggii
The subclass Crossopterygii (coelacanths) is
characterized by a type of primitive scale
called a cosmoid scale, two dorsal fins, and
fleshy paired fins that contain skeletal
Scientists used to think that this entire
subclass of fishes was extinct. Then in 1938, a
living coelacanth (Latimeria chalumnae) was
discovered off the coast of Southeast Africa.
Several specimens have since been collected.
Class Actinopterygii
The subclass Actinopterygii includes all other
living bony fishes. Actinopterygians are
characterized by fins that are supported by
bony elements called rays.
Orders and Families
All orders of bony fishes end in the suffix
 While there is debate over how certain fishes
should be classified, scientists recognize more
than 500 different bony fish families.
 The names of bony fish families all end in the
suffix "dae".
Genera and Species
More than 28,000 species of bony fishes have
been documented. It's likely that many more,
including some deep-sea species, have yet to be
Fossil Record
Primitive fishes date back to the
Cambrian period, about 550 million years
ago. These jawless fishes lived relatively
unchanged over the following 100 million
 The Devonian period, about 360 to 400
million years ago, is known as the "Age of
Fishes", because of the abundance and
diversity of fishes that appeared during
this period.
Fossil Record
◦ In the Devonian, fishes began to develop jaws
and paired fins. All four living classes of fishes
and the three subclasses of Osteichthyes were
established by the mid-Devonian.
◦ Many species of fish that lived during the
Devonian are now extinct.
Fossil Records
Bony fishes continued to evolve after the
Devonian period. Most modern orders of
bony fishes probably evolved during the
Triassic period, about 200 million years ago.
Today, the Actinoptergians are the dominant
vertebrates in the oceans and in freshwater
The most recently evolved orders of bony
fishes include the Pleuronectiformes
(flatfishes) and Tetraodontiformes
(triggerfishes, pufferfishes, and molas).
Habitat & Distribution
Bony fishes inhabit almost every body of water.
They are found in tropical, temperate, and polar
seas as well as virtually all fresh water
 Some species of bony fishes live as deep as 11 km
(6.8 mi.) in the deep sea. Other species inhabit
lakes as high as 5 km (3.1 mi.) above sea level.
 About 58% of all species of bony fishes (more
than 13,000 species) live in marine environments.
Although only 0.01% of the earth's water is fresh
water, freshwater fishes make up about 42% of
fish species (more than 9,000 species).
Bony fishes live in fresh water, sea water, and
brackish (a combination of fresh water and salt
water) environments.
 The salinity of sea water is about 35 ppt (parts
per thousand). Some species can tolerate
higher-salinity environments. Some species of
gobies can tolerate salinity levels as high as 60
Fishes live in virtually all aquatic habitats.
Different species of fish are adapted for
different habitats: rocky shores, coral reefs, kelp
forests, rivers and streams, lakes and ponds,
under sea ice, the deep sea, and other
environments of fresh, salt, and brackish water.
Some fish are pelagic: they live in the open
ocean. For example, tunas (several species in
the family Scombridae, subfamily Thunninae)
are pelagic fishes.
Some species, such as the flatfishes (order
Pleuronectiformes) are adapted for living
along the bottom. Certain fishes, such as
gobies (family Gobiidae) even burrow into
the substrate or bury themselves in sand.
Ocean sunfish (family Molidae) are most
often spotted at the ocean's surface.
Some lungfishes "hibernate" throughout a
summer drought season, buried under the mud
of a dried-up pond.
 Several fish species live in freshwater habitats in
the darkness of caves.
Depending on the species, bony fishes can live at
various temperatures. Some live at extreme
temperatures. Some desert pupfish (Cyprinodon
macularius) live in California hot springs that
reach temperatures greater than 45°C (113°F).
 At the opposite extreme, some species of bony
fishes can survive freezing temperatures of the
Arctic and Antarctic. Certain glycoprotein
molecules present in the blood of these speciallyadapted fishes lower the freezing point of the
blood. The arctic cod (Boreogadus saida) can
survive temperatures as low as -2°C (28°F).
In general, fishes rely on oxygen dissolved in
water for respiration.
 Some species of bony fishes require large
amounts of dissolved oxygen. The brown trout
(Salmo trutta) requires up to 11 mg of dissolved
oxygen per liter (11 ppm, or parts per million).
 Misgurnus fossillis, a type of loach, can survive in
water with an oxygen concentration as low as
0.5 mg per liter (0.5 ppm).
Mudskippers (family Periophthalmidae) can
carry a small amount of water in their gill
cavities. They commonly spend time on land,
returning to mud holes when their water supply
begins to evaporate.
 African lungfishes (subclass Dipnoi) gulp air into
a "lung" for respiration. In fact, these fishes must
have access to the water's surface or they will
Thousands of species of bony fishes are
less than a few centimeters long as adults.
Among the smallest is the endangered
dwarf pygmy goby (Pandaka pygmaea).
Adult males reach just 15 mm (0.6 in.),
and adult females reach only about 9 mm
(0.4 in.).
Some species can reach tremendous sizes
- much larger than a human. The longest
bony fish is the oarfish (Regalecus glesne),
which can reach 11 m (36 ft.).
 Among the heaviest of the bony fishes is
the common ocean sunfish (Mola mola),
which lives throughout warm and
temperate seas worldwide. A large sunfish
can reach 3.3 m (10.8 ft.) and 2,300 kg
(5,071 lb.).
Many sturgeons (family Acipenseridae) grow
very large. The largest is the beluga sturgeon
(Huso huso), which inhabits the Caspian,
Black, and Adriatic Seas and can reach 5 m
(16.4 ft.) and 2,000 kg (4,409 lb.).
Black marlin (Makaira indica) reach 4.7 m
(15.4 ft.) and 750 kg (1,653 lb.).
The European wels catfish (Silurus glanis)
reaches 5 m (16.4 ft.) and about 300 kg (661
Body Shape
Bony fishes show great variety in body shape,
but the "typical" fish body shape is roughly
cylindrical and tapering at both ends. This
characteristic fusiform shape is quite energy
efficient for swimming. Compared to other
body shapes, this body shape creates less drag
(the opposing force an object generates as it
travels through water).
Body Shape
Various species of fishes deviate from the
fusiform body shape in three ways:
compression, depression, and
 A laterally compressed (flattened, side-toside) body shape is common in bony fishes
that live in dense cover or within coral reefs.
Butterflyfishes (family Chaetodontidae) are
an example of bony fishes with a laterally
compressed body shape.
Body shape
A depressed (flattened, top-to-bottom)
body shape is common in bottomdwelling fishes. Goosefishes (family
Lophidae) and batfishes (family
Ogcocephalidae) are examples of bony
fishes with a depressed body shape.
The body shape of an eel (for example,
the morays, family Muraenidae) is an
extreme example of anelongated shape.
Most fish species have pigmentation. Pigment is
mostly contained in cells called chromatophores.
Most fishes can contract and expand their
chromatophores to change colors.
 Reflective cells called iridocytes can change color
 Because the different wavelengths of light are
absorbed at various depths, fishes may appear a
different color underwater than at the surface.
 Some fish, such as the ghost glass catfish
(Kryptopterus bicirrhis), lack pigmentation.
Some fish bioluminate (emit light).Certain
pigments (called luciferins) emit light when
Some fish produce light in luminescent
organs or in cells called photophores. In
some fish, it is light-producing bacteria that
live in or on the fish that actually produce
the light.
Depending on species, bioluminescence may
attract mates, deter or confuse predators,
attract prey, or act as "headlights" to help a
fish see in the dark.
All fishes have fins. Bony fish families show
various degrees of fin fusion and reduction.
 Fins help stabilize or propel a fish in the water.
 Except in the lungfishes and the coelacanth, fins
lack bones. In Actinopterygians, fins are
supported by structures called rays.
The spiny fin rays of some species are
associated with venom glands. Fishes in the
family Scorpaenidae include the stonefish
(Synanceja spp.), the lionfish (Pterois spp.), and
the scorpionfish (Scorpaena spp.) - some of the
most venomous fishes in the world. Glands in
the dorsal, anal, and pelvic spines produce
venom that is intensely painful and occasionally
fatal to humans.
Fishes have two kinds of fins: paired fins
(pectoral and pelvic) and median fins (dorsal,
caudal, and anal)
Typically, the paired pectoral fins help a fish
turn. In some fishes, pectoral fins are adapted
for other functions.
Paired pelvic fins add stability, and some
fishes use them for slowing. In the clingfishes
(family Gobiesocidae), the pelvic fins are
adapted as a sucking appendage, which helps
a fish hold on to stationary objects on the
ocean bottom.
The dorsal fin may be a single fin or separated into
several fins. In most bony fishes, the dorsal fin is used
for sudden direction changes and acts as a "keel",
keeping the fish stable in the water. In some fishes, the
dorsal fin is adapted for other functions.
The caudal fin, or tail, is responsible for propulsion in
most bony fishes. Caudal fins come in many shapes.
Many continuously swimming fishes have forked
caudal fins. Fishes with lunate caudal fins, such as
tunas, tend to be fast swimmers that can maintain
rapid speed for long durations.
The anal fin adds stability. In some fishes,
the anal fin is adapted for other functions.
Some species of bony fishes have reduced
or absent fins. For example, morays
(family Muraenidae) lack pectoral fins and
pelvic fins. Several species lack an anal fin.
Eye size and position vary depending on the habitat
and behavior of the species.
 In most species, the gills are protected by a flexible
plate called an operculum. Most bony fishes have a
single pair of gill openings. Some bony fishes such as
eels (family Anguillidae) have a pair of gill holes or
pores that aren't covered by an operculum.
 The nostrils of most bony fishes have no connection
with the mouth or gills. In some bony fishes (such as
eels), the nostrils' incurrent and excurrent openings
are widely separated.
 Mouth shape and size are good indications of bony
fish's feeding habits.
Most species of bony fishes are covered with
and protected by a layer of plates called scales.
 There are four different kinds of bony fish
scales: cosmoid, ganoid, cycloid, and ctenoid.
True cosmoid scales are found only on extinct
Crossopterygians. The inner layer of a cosmoid
scale is compact bone. On top of this bone layer
lays a spongy layer and then a layer of cosmine (a
type of dentin). The upper surface is enamel.
 Gars (family Lepisosteidae), bichirs, and reedfishes
(family Polypteridae) have ganoid scales. They are
similar to cosmoid scales, but a layer of ganoin (a
hard, enamel-like substance) lies over the cosmine
layer and under the enamel. Ganoid scales are
diamond-shaped, shiny, and hard.
Most bony fishes have cycloid or ctenoid scales. Both
cycloid and ctenoid scales consist of an outer layer of
calcium and an inner layer of connective tissue.
Cycloid scales overlap from head to tail, an
arrangement that helps reduce drag as a fish swims.
Cycloid scales are circular and smooth. They are most
common on fishes with soft fin rays.
Ctenoid scales have a characteristic toothed edge.
They are most common on fishes with spiny fin rays.
As a fish grows, cycloid and ctenoid scales add
concentric layers.
Body Spines
Body spines are modified scales.
 Protective spines are common in slowswimming fishes and others that need to
protect themselves without moving.
 Some fishes actively engage spines.
A fish secretes a layer of mucus that covers
its entire body. Mucus helps protect a fish
from infection.
In some bony fishes, mucus may serve
additional functions.
◦ Some species of parrotfishes (family Scaridae)
envelop their bodies in mucous bubbles at night
while they rest. This mucous barrier may "hide"
the parrotfish from nocturnal predators that rely
on their sense of smell to locate prey.
◦ Young discus (Symphysodon discus) feed on the
parent fish's mucus.
Skeletal System
The skeleton of bony fishes is made of bone and
cartilage. The vertebral column, cranium, jaw,
ribs, and intramuscular bones make up a bony
fish's skeleton.
 The skeleton of a bony fish gives structure,
provides protection, assists in leverage, and
(along with the spleen and the kidney) is a site
of red blood cell production.
Muscular System
The muscles of the tail and trunk consist
of a series of muscle blocks called
 The myotomes usually resemble a
sideways letter "W". A connective tissue
called myosepta separates the myotomes.
 A horizontal septum separates the
myotomes into dorsal (top) myotomes
and ventral (bottom) myotomes.
Nervous System
The nervous system of fishes is poorly
developed compared to that of other
A bony fish's brain is divided into three
sections: the forebrain, the midbrain, and
the hindbrain.
The forebrain is responsible for the bony
fish's ability to smell. Bony fishes that have an
especially good sense of smell, such as eels,
have an enlarged forebrain.
Nervous system
The midbrain processes vision, learning,
and motor responses. Blind bony fishes, such
as blind cavefishes in the family
Amblyopsidae, have a reduced midbrain.
The hindbrain (medulla oblongata and
cerebellum) coordinates movement, muscle
tone, and balance. Fast-swimming bony fishes
usually have an enlarged hindbrain.
Cardiovasular System
A bony fish's heart has two chambers: an
atrium and a ventricle.
 The venous side of the heart is preceded
by an enlarged chamber called the sinus
 The arterial side of the heart is followed
by a thickened muscular cavity called the
bulbus arteriosus.
Digestive System
The esophagus in bony fishes is short and
expandable so that large objects can be
swallowed. The esophagus walls are layered with
 Most species of bony fishes have a stomach.
Usually the stomach is a bent muscular tube in a
"U" or "V" shape. Gastric glands release
substances that break down food to prepare it
for digestion.
 At the end of the stomach, many bony fishes have
blind sacs called pyloric caeca. The pyloric caeca
are an adaptation for increasing the gut area; they
digest food.
Swim Bladder
Many species of bony fishes have a gas-filled
bladder called a swim bladder.
 Apparently the swim bladder originally
developed in fish as an organ of respiration,
as evidenced by the "lung" of the lungfishes.
 In modern bony fishes that possess a swim
bladder, the organ serves principally in
maintaining neutral buoyancy.
 In some fishes the swim bladder has adapted
to function as a sound amplifier.
Acoustic Senses
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).
 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 (Carassius auratus), a series of small bones
connects the swim bladder to the ear.
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.
The eyesight in some species of bony fishes
may be well developed. Goldfish (Carassius
auratus) have excellent visual acuity up to 4.8
m (16 ft.) away.
Bony fishes have taste buds in their
mouths. Some species have taste buds
along the head and ventral side of the
 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.
Some bony fishes in the families Electrophoridae,
Gymnotidae, and Mormyridae produce a lowvoltage 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.
Fertilization and Embryonic
Some species release unfertilized eggs and
sperm.Young develop from eggs that are
fertilized in the water.
Some species have internal fertilization;
these species mate. For species with internal
fertilization, there is great variation in the
development stage at which offspring are
released: fertilized eggs, larvae, juvenile fish,
or even sexually mature adults.
Oviparous bony fishes release eggs, and the
developing embryo is nourished by a yolk
In ovoviviparous fishes, one parent (usually
female) retains the fertilized eggs in her
body, and the developing embryo is
nourished by a yolk sac formed prior to
fertilization. There is no nutrient connection
between the parent and the developing
In viviparous fishes, the female retains the
fertilized eggs in her ovary or uterus, and
the developing embryo is nourished by
connection with the mother.
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