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Marine Conservation Science and Policy
Learning Service Program
Jawless fishes including the hagfishes and lampreys are a very small group of fishes
comprising two families. They have a cartilage skeleton (no bone), lack vertebral centra
and paired fins, and have a series of pores for gas exchange on the side of the body (no
gill slits). Jaws are absent and the mouth is adapted for sucking (hagfishes) and sucking
and rasping (lampreys). They are small to moderate sized with elongate (eel-like)
bodies. The hagfishes are found from coastal to deepwater and appear to feed on dead
and decaying organisms. Bony fishes are the largest group of marine fishes and
include most of the fishes exploited by humans. They have a bony skeleton, generally
including bony fins, jaws (often with teeth), operculum or gill plate, and often have
scales on the skin. Bony fishes are adapted for many forms of life. Some are adapted
for bottom living in shallow coastal waters. Others are adapted to life on the deep sea
floor at thousands of meters.
Module 2: Ichthyology
Section 3: Jawless and Bony fishes
Sunshine State
Standards
SC.912.L.15.1,
SC.912.L.15.6,
SC.
912.L15.7, SC.912.L.15.13,
SC.L.15.14, SC.912.17.2, SC.912.l.17.3, SC.912.L.17.7
Objectives
 Understand main characteristics of class Agnatha
 Identify organisms found in the jawless fish group
 Understand main characteristics of class Osteichthyes
 Identify main groups of the bony fishes
______________________________________________________________________
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Vocabulary
Bones- are rigid organs that form part of the endoskeleton of vertebrates. They function
to move, support, and protect the various organs of the body, produce red and white
blood cells and store minerals.
Ectothermic- refers to organisms that control body temperature through external
means. As a result, organisms are dependent on environmental heat sources and have
relatively low metabolic rates.
Fish- is any aquatic vertebrate animal that is covered with scales, and equipped with
two sets of paired fins and several unpaired fins. Most fish are "cold-blooded", or
ectothermic, allowing their body temperatures to vary as ambient temperatures change.
Scales- is a small rigid plate that grows out of an animal's skin to provide protection.
Background
What is a fish?
A fish is an aquatic vertebrate that respires using gills, is ectothermic, has fins, and has
a skin that is usually with scales. The taxonomic term for fish is Pisces.
"Fishes or Fish?
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Although people generally use the word "fish" for both singular and plural, most
scientists usually make a distinction between them. From the scientist's point of view,
then, what's the difference between "fish" and "fishes"?


Both words can refer to more than one fish. The word "fishes" refers to more than
one KIND of fish: If you have a tub with three bluegills in it, say: "I have several
fish in this tub."
If you have a bucket with a bluegill, a largemouth bass, and a paddlefish in it,
say: "I have several fishes in this tub."
Jawless fishes: Class AGNATHA
In traditional classifications, the
hagfish, lampreys, and extinct
armored jawless fish are grouped
together in the Class Agnatha.
Agnatha (Greek, "no jaws") is a
superclass of jawless fish in the
phylum
Chordata,
subphylum
Vertebrata. The group excludes all
vertebrates with jaws, known as gnathostomes.
Hagfish are not members of
the subphylum Vertebrata, as
hagfish
do
not
have
vertebrae; they are rather
classified
in
the more
inclusive group Craniata. In
addition to the absence of
jaws, modern agnathans are
characterized by absence of
paired fins; the presence of a
notochord both in larvae and
adults; and seven or more
paired gill pouches. There is
a light sensitive pineal eye
(homologous to the pineal
gland in mammals). All living
and most extinct Agnatha do
not have an identifiable
stomach or any appendages.
Fertilization and development
are both external. There is no
parental care in the Agnatha
class. The Agnatha are
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ectothermic or cold blooded, with a cartilaginous skeleton, and the heart contains 2
chambers.
While a few scientists still regard the living agnaths as only superficially similar, and
argue that many of these similarities are probably shared basal characteristics of
ancient vertebrates, recent classifications clearly place hagfish (the Myxini or
Hyperotreti), with the lampreys (Hyperoartii) as being more closely related to each other
than either is to the jawed fishes.
Metabolism
Agnathans are ectothermic, meaning they do not regulate their own body temperature.
Agnathan metabolism is slow in cold water, and therefore they do not have to eat very
much. They have no distinct stomach, but rather a long gut, more or less homogenous
throughout its length. Lampreys are parasitic, feeding off of other fish and mammals.
They rely on a row of sharp teeth to shred their host. Fluids preventing clotting are
injected into the host, causing the host to yield more blood. Hagfish are decomposers,
eating mostly dead animals. They also use a sharp set of teeth to break down the
animal. Agnathan feeding habits have limited their ability to advance evolutionarily. The
fact that all Agnathan teeth are not able to move up and down limit their possible food
types.
Body covering
The only modern Agnathan
body covering is skin, with
neither dermal or epidermal
scales. The skin of hagfish
has copious slime glands, the
slime
constituting
their
defence mechanism. Many
extinct agnathans sported
heavy dermal armour or
small mineralized scales.
Skeleton
The internal skeleton of the
Agnatha is not bony but
rather cartilaginous (made up
of dense connective tissue). The somewhat rudimentary skull never ossifies and
remains a chondrocranium throughout life. Also, Agnathans retain a notochord in
adulthood, a characteristic distinctive of the class. This notochord is a cartilagious rod
that forms the basis of the vertebral column in higher vertebrates.
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Reproduction
Fertilization is external, as is development. There is no parental care. Not much is
known about the hagfish reproductive process. It is believed that hagfish only have 30
eggs over a lifetime. Most species are hermaphrodites. There is very little of the larval
stage that characterizes the lamprey. Lampreys can only reproduce once. After external
fertilization, the lamprey's cloacas remain open, allowing a fungus to enter their
intestines, killing them. Lampreys reproduce in freshwater river beds, and bury their
eggs about two centimeters underground. Lampreys work in pairs buildings the egg
nests. Lampreys go through four years of larval development before becoming adults.
They also have a certain unusual form of reproduction.
General characteristics





jaws absent (there is a mouth, but it lacks internal cartilaginous or bony supports)
paired limbs absent (a single pair may be present in fossil forms)
cartilaginous endoskeletons are present
larval forms resemble lancelets
Living forms are elongate, scaleless, slimy parasites and scavengers
INFRAPHYLUM MYXINOIDEA






includes the living and fossil hagfish.
6 genera, 60 species
exclusively marine
elongate (eel-like)
scaleless
many mucous glands present for antipredator defense (hagfish slime)
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





o
feed
on
polychaete
worms, shrimp, and
dead or dying fish
o
attach to fish, form a
knot in the tail and pass
it forward to rip off flesh.
usually enter body cavity
and feed on soft parts
most "eel skin" is bycatch of scavenging hagfishes
nasal opening; pineal not exposed
poorly developed eyes (lensless)
no vertebrae
unsupported fin rays
partially developed cartilaginous braincase and gill supports
Order PETROMYZONTIFORMES


lampreys
1. have a skeleton of cartilage, previously interpreted as descended from the
ostracoderms, jawless fish with an external bony armor, which lampreys
have secondarily lost.
2. currently researchers suggest the absence of a dermal skeleton in
lampreys and absence of other features is primitive.
Characters
1. dorsal nasal opening
2. pineal eye
3. cartilaginous braincase
4. branchial skeleton, vertebrae, and fin rays
5. seven gill pouches open directly to exterior
6. osmotic regulators
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7. ammocetes larva

Ventral view of oral sucker and mouth of the lamprey.
Note the horny rasping teeth. Many lampreys are
parasites of bony fishes.

Europeans have long considered lampreys a delicacy.
The lamprey has, so far, failed to whet North American
appetites.
Bony Fishes: Class OSTEICHTHYES
Osteichthyes also called bony fish, are a taxonomic group of fish that have bony, as
opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is
an extremely diverse and abundant group consisting of over 29,000 species. It is the
largest class of vertebrates in existence today. Osteichthyes is divided into the rayfinned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii).
Most bony fish belong to the ray-finned fish (Actinopterygii); there are only eight living
species of lobe-finned fish (Sarcopterygii), including the lungfish and coelacanths.
Biology
All bony fish possess gills. For the majority this is their
sole or main means of respiration. Lungfish and other
osteichthyan species, are capable of respiration
through lungs or vascularized swim bladders. Other
species can respire through their skin, intestines,
and/or stomach.
Osteichthyes are primatively ectothermic (cold
blooded), meaning that their body temperature is
dependent on that of the water. But some members of
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the family scombridae such as the swordfish and tuna have achieved various levels of
endothermy. They can be any type of heterotroph: omnivore, carnivore, herbivore, or
detritivore.
Some bony fish are hermaphrodites, and a number of species exhibit parthenogenesis.
Fertilization is usually external, but can be internal. Development is usually oviparous
(egg-laying) but can be ovoviviparous, or viviparous. Although there is usually no
parental care after birth, before birth parents may scatter, hide, guard or brood eggs,
with sea horses being notable in that the males undergo a form of 'pregnancy', brooding
eggs deposited in a ventral pouch by a female.
DISTRIBUTION
1. Bony fishes inhabit almost every body of water. They are found in tropical, temperate,
and polar seas as well as virtually all fresh water environments.
2. 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.
3. 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).
HABITAT
1. 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 ppt.
2. 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.
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• 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.
3. 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 specially-adapted fishes lower the freezing point of the blood. The arctic
cod (Boreogadus saida) can survive temperatures as low as -2°C (28°F).
4. 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).
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• 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 drown.
MIGRATION
1. Most bony fishes have small home ranges.
2. Some species of bony fishes migrate great distances. Food and habitat availability,
reproduction, environmental cycles and temperature change may be causes of
migration for some species.
• Almost all tuna species are migratory. Albacore (Thunnus alalunga) migrate across the
Pacific Ocean from the coast of California to the coast of Japan, more than 8,500 km
(5,270 mi.). Data from albacore tagging studies indicate that they travel an average of
26 km (16 mi.) per day. Tagged northern bluefin tuna (Thunnus thynnus) have migrated
7,700 km (4,774 mi.) across the Atlantic Ocean in 119 days, about 65 km (40 mi.) per
day.
• Billfishes (family Istiophoridae) are highly migratory. A black marlin (Makaira indica)
that was tagged and released off Cabo San Lucas, Mexico, was recovered off Norfolk
Island in the South Pacific, more than 10,680 km (6,622 mi.) away.
3. Some bony fish species are diadromous: they migrate between fresh and marine
environments.
• Some fish are catadromous: they live in freshwater environments but migrate
downriver to the ocean to spawn. The freshwater eels (family Anguillidae) develop in
marine environments then move into freshwater rivers to live.
• Anadromous fishes live most of their lives in the ocean, but migrate into freshwater
environments to spawn. The sockeye salmon (Oncorhynchus nerka) may travel more
than 3,600 km (2,232 mi.) up the Yukon River to spawn.
SIZE
1. 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.).
2. 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.).
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• 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 lb.).
BODY SHAPE
1. 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
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travels through water).
2. Various species of fishes deviate from the fusiform body shape in three ways:
compression, depression, and elongation.
• A laterally compressed (flattened, side-to-side) 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.
•
A
depressed
(flattened,
top-tobottom) 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 an
elongated shape.
3. The body shape of
some species differs
from
or
combines
features
of
these
typical fish body forms.
Examples
include
boxfishes
(family
Ostraciidae ), ocean
sunfishes
(family
Molidae),
seahorses
(Hippocampus spp.),
the weedy seadragon
(Phyllopteryx
taeniolatus), and the leafy seadragon (Phycodurus eques).
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COLORATION
1. 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 rapidly.
• 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.
2. Coloration may camouflage a fish.
• Most species of fishes are countershaded: the dorsal (top) surface is darker than the
ventral (underneath) surface. When light comes from above, the animal appears
inconspicuous. The dorsal side of a countershaded fish blends in with the dark ocean
depths or ocean bottom when viewed from above. The ventral side blends in with the
lighter surface of the sea when viewed from below. A countershaded fish is harder for
predators and prey to spot.
• Some fish are colored so that they blend in with their environment. Many bottom
dwelling fishes match the substrate and even change color when they move to a new
location. The northern pike's (Esox lucius) colors blend in with weedy areas where it
lurks in wait for prey.
3. Some fishes show disruptive coloration. Their colors and pattern obscure the outline
of the fish by contradicting the animal's body shape.
4. Highly distinctive elements may confuse predators. For example, some fish have a
false eyespot that can fool a predator into striking in the wrong direction, allowing the
fish to escape.
5. In some species, coloration serves as advertisement to other animals.
• Some fishes rely on coloration for species recognition and sexual distinction. The
stoplight parrotfish (Sparisoma viride) female and male are completely different colors,
although they are similar in shape and size. Some species of fishes become brighter in
color during breeding season to attract potential mates.
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• In some species, coloration may trigger behavior. After establishing a territory, the
male stickleback's (family Gasterosteidae) belly turns red. He then actively defends his
territory only from other fish with red bellies, notably other male sticklebacks.
• A garibaldi's (Hypsypops rubicundus) bright orange color warns other fishes that the
garibaldi will defend its territory.
6. Some fish change color.
• Some species change color
and markings as they grow from
juveniles to adults. Juvenile
garibaldi
(Hypsypops
rubicundus), for example, are
dark orange with bright blue
spots; adults are bright orange.
• Fish of some species can
change
sex,
which
is
accompanied by color change.
Examples include the angelfishes (Family Pomacanthidae) and most species of
wrasses (Family Labridae).
• Some color change may be rapid and temporary. Alarmed fish, for instance, often
change color. Some bottom-dwelling fishes change color almost instantly to match the
substrate.
7. Some fish bioluminate
(emit light).
• Certain pigments (called
luciferins) emit light when
oxidized.
• Some fish produce light in
luminescent organs or in
cells called photophores. In
some fish, it is lightproducing 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.
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FINS
1. All fishes have fins. Bony fish families show various degrees of fin fusion and
reduction.
2. Fins help stabilize or propel a fish in the water.
3. Except in the lungfishes and the coelacanth, fins lack bones. In Actinopterygians, fins
are supported by structures called rays.
• Some bony fishes have soft, flexible fin rays.
• Other bony fishes have spiny, rigid fin rays at the leading edges of the dorsal, anal,
and pelvic fins.
• Both soft and spiny fin rays are modified scales.
• 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.
4. 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.
° Some bony fishes, such as the hawkfishes (Cirrhitichthys spp.) use their pectoral fins
to help them "perch" at the bottom and on reef areas. Mudskippers (family
Periophthalmidae) support themselves on land with their pectoral fins.
° The pectoral fins of flying fishes (family Exocoetidae) are extremely long, an
adaptation that allows flying fish to glide over water as far as 150 m (492 ft.) and remain
airborne as long as 20 seconds.
° Some bottom-dwelling fishes such as threadfins (family Polynemidae) have taste buds
and touch receptors on their pectoral fins to locate food.
° For some fishes, such as wrasses (family Labridae), pectoral fins are the main source
of power for swimming.
• 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.
15
• 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.
° In the anglerfishes (order Lophiiformes), the dorsal fin is a lure that attracts prey.
° The dorsal fin of remoras (family Echeneidae) is modified into a sucking disc.
Remoras cling to large fishes and mammals with this dorsal disc and are carried along
as hitchhikers.
° An African knifefish (Gymnarchus niloticus) undulates its dorsal fin to move forward or
backward.
• 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.
° The black ghost knifefish (Apteronotus albifrons) undulates its anal fin as a means of
propulsion.
° In some bony fishes, the anal fin plays a role in reproduction. The anal fin may fan
sperm over eggs, or may concentrate sperm into a particular area.
5. 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.
HEAD
1. Eye size and
position
vary
depending
on
the habitat and
behavior of the
species.
16
• Some species have eyes positioned for a 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.
• In flatfishes in the order Pleuronectiformes, one eye migrates across the top of their
skull during development. Very young juveniles are free-swimming and have an eye on
each side of the head. Adults live on the sea bottom, lying and swimming on one side.
The eye that would typically be on that side of the body is on the dorsal (top) of the fish,
adjacent to the other eye.
2. 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.
3. 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.
4. Mouth shape and size are good indications of bony fish's feeding habits.
• Most bony fishes have mouths at the front end of the head.
• Some bottom-feeding species have mouths on the underside of the snout, angled
toward the bottom.
• Some surface-feeding species have mouths that angle upwards.
• Butterflyfishes (family Chaetodontidae) have thin snouts and small mouths that are
useful in reaching food located in crevices and cracks.
• Some species of bony fishes, like the goatfishes (family Mulidae), have fleshy barbels
that fringe the mouth. These barbels can detect food.
SCALES
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1. Most species of bony fishes are covered with and protected by a layer of plates called
scales.
2. 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. The living
coelacanth has modified cosmoid scales, which are thinner than true cosmoid scales.
• 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.
18
° As a fish grows, cycloid and ctenoid scales add concentric layers.
3. Some bony fishes may have scales only on portions of their body, and some species
have no scales.
BODY SPINES
1. Body spines are modified
scales.
2. Protective spines are
common in slow-swimming
fishes and others that need to
protect themselves without
moving.
3. Some fishes
engage spines.
actively
• Most surgeonfishes (family
Acanthuridae) have mobile,
razor-sharp precaudal fin
spines that they use to protect
themselves.
• The triggerfishes (family Balistidae) have three dorsal spines that lock together. These
spines may allow a triggerfish to securely lodge itself between rocks and keep predators
from swallowing it.
• Some pufferfishes (family Tetraodontidae) have spines that cover the entire body. The
spines lie flat until the pufferfish inflates its body.
MUCUS
1. A fish secretes a layer of mucus that covers its entire body. Mucus helps protect a
fish from infection.
2. 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.
19
SKELETAL SYSTEM
1. 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.
2. 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
1. The muscles of the tail and trunk consist of a series of muscle blocks called
myotomes. 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.
2. Jaw muscles usually consist of adductor muscles that close the jaw and abductor
muscles that open the jaw.
20
3. Fin muscles consist of abductor and adductor muscles that move the fins away from
and close to the body, and erector muscles that provide stability and flexibility in the
fins.
NERVOUS SYSTEM
1. The nervous system of fishes is poorly developed compared to that of other
vertebrates.
2. 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.
• 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.
3. The spinal cord and a matrix of nerves serve the rest of the body.
CARDIOVASCULAR SYSTEM
21
1. 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 venosus. The arterial
side of the heart is followed by a thickened muscular cavity called the bulbus arteriosus.
2. Blood flow.
• The sinus venosus receives oxygen-depleted blood from the body. A valve at the end
of the sinus venosus opens into the atrium.
• The atrium has thick, muscular walls. The atrium receives oxygen-depleted blood and
pumps it into the ventricle.
• The ventricle is the largest and most muscular chamber of the heart. When filled with
blood, it constricts, forcing the blood through the bulbus arteriosus.
• Blood flows through the bulbus arteriosus into the ventral aorta. A valve or series of
valves in the bulbus arteriosus controls blood flow into the ventral aorta
.
• From the ventral aorta, blood flows to the gill filaments, where it is oxygenated.
• Oxygenated blood flows from the gill filaments to the organs of the head and body. A
complex system of arteries, veins, and capillaries circulates blood through the body and
returns the blood to the sinus venosus.
3. Some tunas (family Scombridae, subfamily Thunninae) maintain a body temperature
several degrees higher than that of the surrounding water. This heat is due to the
modified circulatory system associated with the red muscle.
• As red muscle functions, it generates heat. Muscle-generated heat warms the blood
circulating through the red muscle, which then travels back to the heart through veins.
Thus, blood returning to the heart from the muscle is warmer than blood traveling from
the heart to the muscle.
• Due to the nearness of arteries and veins, heat passes from warmer veins to cooler
arteries within the fish's body, rather than dissipating to the cooler environment. This
modified circulatory system retains heat in the red muscle.
• A higher body temperature is an adaptive advantage for high-speed swimming.
• A similar modified circulatory system warms the brain and eye of some species of
tunas and billfishes (family Istiophoridae).
DIGESTIVE SYSTEM
22
1. The esophagus in bony fishes is short and expandable so that large objects can be
swallowed. The esophagus walls are layered with muscle.
2. 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.
3. 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.
4. The pancreas secretes enzymes into the intestine for digestion.
5. Most food absorption takes place in the intestine. The length of the intestine in bony
fishes varies greatly. Plant-eating bony fishes generally have long, coiled intestines.
Carnivorous bony fishes have shorter intestines.
6. The digestive system terminates at the anus.
23
RESPIRATORY SYSTEM
1. Water enters the gill chamber through a fish's mouth and exits through gill openings
under the operculum. Blood flowing through the gill filaments absorbs oxygen from the
water.
2. Some fish have adaptations for getting oxygen from air. Lungfish must return to the
surface to breathe air. A lungfish swallows air to fill up an air sac or "lung". This lung is
surrounded by veins that bring blood to be oxygenated. Its gills alone can't keep a
lungfish supplied with enough oxygen to live. Other species such as tarpon (family
Elopidae) can gulp air at the surface to supplement their oxygen demand.
3. Some species of bony fishes can absorb considerable amounts of oxygen through
their skin.
24
SWIM BLADDER
1. Many species of
bony fishes have a
gas-filled
bladder
called a swim bladder.
2. Apparently the swim
bladder
originally
developed in fish as an
organ of respiration, as
evidenced by the "lung"
of the lungfishes.
3. In modern bony
fishes that possess a
swim
bladder,
the
organ
serves
principally in maintaining neutral buoyancy.
4. In some fishes the swim bladder has adapted to function as a sound amplifier.
OSMOREGULATION
1. Both marine and freshwater fishes regulate the movement of water across their body
surfaces.
2. The tissues of marine fishes are less salty than the surrounding water, so water
continually leaves the body of a marine fish through its skin and gills. To keep from
becoming dehydrated, a marine fish drinks large amounts of water and produces a
small amount of concentrated urine. In addition, its gills are adapted to secrete salt.
3. The tissues of a freshwater fish are saltier than its surrounding environment, so water
is continually entering the body of a freshwater fish through its skin and gills. Freshwater
fishes do not drink water, and they produce large amounts of dilute urine.
ACOUSTIC SENSES
1. 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
25
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 (Carassius auratus), 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.
2. Lateral line.
• Like the ear, the lateral line senses vibrations. It functions mainly in detecting lowfrequency 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.
26
• 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.
3. In bony fishes, frequency range of sound production does not appear to be correlated
with hearing sensitivity.
4. Most species of bony fishes probably detect prey by sound.
5. In water, sound travels more than four times the speed of sound through air.
EYESIGHT
1. 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 shallowwater 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 tapetum lucidum 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.
2. 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.
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 californiensis) is born with eyes that degenerate as the goby
matures.
27
TASTE
1. Bony fishes have taste buds in 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.
3. Taste may be responsible for the final
acceptance or rejection of prey items.
SMELL
1. Olfactory cells in the nasal sac detect tiny amounts of chemicals in solution.
2. 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.
ELECTRORECEPTION
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. 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.
2. Some other fishes produce stronger electric currents for stunning prey.
28
ACTIVITY
1. Some species of fish, such as tunas, swim continually.
2. Many species spend most of their time lying on the ocean bottom.
Bottom-dwellers
include
stonefishes
(Synanceja
spp.),
flatfishes
Pleuronectiformes), and blennies (family Blennidae).
(order
3. Certain species have peak activity times during a day.
• Morays (family Muraenidae) are an example of fish that are more active at night.
• Butterflyfishes (family Chaetodontidae), parrotfishes (family Scaridae) and others are
most active during the daytime.
• Some bony fish species are most active at dawn and dusk.
SCHOOLING
1. Many species of small bony
fishes swim together in a
coordinated fashion, called
schooling.
• Schooling is an adaptation for
avoiding
predators:
An
individual fish has a lesser
chance of being eaten by a
predator when in a school than
when alone. A school of small
fish may give the impression of
a large animal, discouraging
predators.
• Schooling poses a hydrodynamic advantage and increases reproductive success. It
also may facilitate locating food sources.
2. Spawning aggregations develop for the purpose of reproduction. These schools
consist mainly of reproductively mature individuals. Cod (family Gadidae) often form
spawning schools.
3. Migrating schools form along migration routes of bony fishes. Migrating schools often
form into other types of schools, such as spawning schools. Salmon (family
Salmonidae) form migrating schools as they travel upstream to spawn.
29
4. Feeding schools develop in the feeding grounds. Feeding schools form primarily due
to the concentration of food organisms. Feeding schools can be comprised of many
different species of bony fishes at different developmental stages.
5. Wintering schools originate in the wintering grounds of bony fishes. Various species
of bony fishes may congregate into areas with the appropriate environmental conditions
for survival during the winter months. These schools often disband after the winter
season.
TERRITORIAL BEHAVIOR
1. Various species of bony fishes have sharply
contrasting
territorial
behavior.
Although
damselfishes (family Pomacentridae) are relatively
small, they are fearless in defending a territory.
However, most large groupers (family Serranidae)
will retreat from their territory if approached by
another animal.
SWIMMING
1. Most species of bony fishes
propel themselves with the
caudal fin, but many species
use other fins for propulsion.
2. Among the slowestswimming bony fishes are the
eels.
3. The Guinness World
Records lists the fastest bony
fish as the sailfish Istiophorus
platypterus, which has been
clocked at 109 km per hour
(68 mph).
SOUND PRODUCTION
1. Many bony fishes produce sound, sometimes in association with reproductive, social,
territorial, or aggressive behavior.
2. Depending on the species, a bony fish can produce sound by rubbing its teeth
together, vibrating its swim bladder, or by flexing and contracting muscles.
30
3. Most sounds produced by bony fishes are below 10,000 Hz.
SYMBIOTIC RELATIONSHIPS
1. Several species of small bony fishes, such as
the cleaner wrasse (Labroides dimidiatus), are
"cleaners" that eat debris and parasites from the
skin and scales of larger fishes.
2. Remoras (family Echeneidae) commonly
attach themselves to sharks or other large
fishes, whales, and sea turtles using a modified
dorsal fin. They eat scraps left over from the
meals of their hosts. They may eat parasites as
well.
3. Some bony fishes have symbiotic
relationships with nonfish species. Clownfishes
(family Pomacentridae) live unharmed among
the venomous tentacles of sea anemones, which
protect the clownfish from potential predators.
(picture on the right)
BONY FISH ATTACKS
1. The great barracuda (Sphyraena barracuda) has been known to attack divers.
Barracuda may confuse shiny objects with the shiny scales of their prey.
2. Piranhas (Serrasalmus spp.) can be voracious predators - they're quick swimmers
with razor-sharp teeth. Piranhas inhabit freshwater river systems in South America.
During periods of low rainfall, streams and rivers recede, and schools of piranhas can
become trapped in shallow ponds. Here their usual prey - smaller fish - are soon
consumed. A school of starving piranhas can consume large animals in minutes. Under
these circumstances, piranhas have been known to attack humans. They are not a
threat to humans when water levels are high and food is abundant.
3. Morays (family Muraenidae) inhabit tropical and warm-temperature waters of the
world. Most species can be found in coral reefs and rocky areas taking shelter in cracks
and crevices. Divers tormenting them, feeding them, or invading their areas have
provoked nonfatal attacks.
NON-SCHOOLING SOCIAL BEHAVIOR
1. Bony fish species show great diversity in social behavior and social organization. For
example, in many wrasse species, social structure includes a large dominant male and
31
many smaller, subordinate females. In contrast, most large predatory bony fishes such
as groupers (family Serranidae) are mostly asocial except during breeding seasons.
FOOD PREFERENCES
AND RESOURCES
1. As a group, bony fishes
have a diverse range of food
preferences.
Some
are
herbivores
(plant-eaters);
some are carnivores (meateaters); some are omnivores
(plant- and meat-eaters); and
some are detritivores (animals
that eat decomposing plants
and animals).
2. As a group, bony fishes
can eat all sizes of plants and
animals, from microscopic
plant plankton to some of the largest marine animals.
3. Some of the animals common in the diets of bony fishes include: annelid worms,
marine snails, mussels, clams, squids, crustaceans, insects, birds, amphibians, small
mammals, and other fishes.
FOOD INTAKE
1. The amount of food a bony fish eats is directly related to its size, its metabolic rate,
and the temperature of its environment.
• Smaller fishes generally have a higher metabolic rate than large fishes of the same
species. Thus, small fishes generally eat proportionately more.
• Warm-water fishes generally require more food than similar-size cold-water fishes. A
fish's body temperature - and its metabolic rate - is determined by the temperature of its
environment.
2. Some bony fishes can go long periods without eating. Some freshwater eels (Anguilla
spp.) can survive more than a year without food.
3. Some researchers have calculated food intake for some species.
• In one study, bluegill (Lepomis macrochirus) - a species of small freshwater fish - ate
between 1% and 35% of their body weight in food per week, depending on water
temperature.
32
• Studies on anchovies (family Engraulidae) during the summer showed a food intake of
about 8% to 10% of body weight per day.
METHODS OF COLLECTING AND EATING FOOD
1. Many bony fishes, such as mackerels and tunas (family Scombridae), seabasses
(family Serranidae), and others are active predators. Like other predators, they often
select weak, ill, injured, or dying prey because it is easier to catch.
2. Some bony fishes, such as anchovies (family Engraulidae) are filter feeders. They
strain plankton from the water with gill rakers.
3. Many bony fishes, including catfishes (Family Ictaluridae) are adapted for bottom
feeding.
4. A species' particular mouth shape and teeth are adapted to accommodate a
particular diet.
• The wolf eel's (family Anarrhichadidae) large
canine teeth grasp its shelled prey. Its blunt
molars crush the shells. (picture on right).
• The blue sucker's (Cycleptus elongatus) thick,
nubby lips help it suck plants from rocks.
• A parrotfish's (family Scaridae) chisel-like teeth,
in a beaklike mouth, nibble on reef-building
corals. These fish are herbivores that eat the algae within the coral. In the process, they
grind the coral's hard exoskeleton and defecate sand.
5. Some bony fishes are quite specialized for feeding. Here are just a few examples:
• A billfish (family Istiophoridae) uses its long bill to stun prey.
• An archerfish (Toxotes jaculatrix) shoots water "bullets" at insects as high as 1.8 m
(5.9 ft.) above the water, knocking them to the water's surface.
• Lying at the bottom of the ocean and looking more like a rock than a fish, a stonefish
(Synanceja spp.) waits for prey to come to it. When an unsuspecting animal swims by,
the stonefish swiftly gulps it.
• The 91 cm (3 ft.) arawana (Osteoglossum bicirrhosum), a freshwater fish of South
America, can leap entirely out of the water to seize small birds.
33
• Some fishes produce strong electric current to stun prey. The electric catfish
(Malapterurus electricus) can produce 350 volts of electricity. The South American
electric eel (Electrophorus electricus) can produce up to 650 volts of electricity.
• Some species of bony fishes, notably the cleaner wrasse (Labroides dimidiatus), are
"cleaners" that pick debris and parasites from larger fishes.
SEXUAL MATURITY
1. Several factors
influence sexual
maturity, including
age, gender, and
size.
2. Fishes become
sexually mature at
various
ages,
depending
on
species.
In
general,
small
species
begin
reproducing at an
earlier age than
large species.
•
Some
bony
fishes
are
sexually mature at
birth. Males of the
dwarf
perch
(Micrometrus
minimus)
can
spawn
immediately after
birth. Although female dwarf perch receive sperm soon after they're born, they do not
bear young for up to a year.
• Some bony fishes become sexually mature shortly after birth. The western
mosquitofish becomes sexually mature within a year.
• Most bony fishes become sexually mature between one and five years.
• It may take ten years or more for some bony fishes to become sexually mature. The
eels (family Anguillidae) become sexually mature at 10 to 14 years of age, and the
sturgeons (family Acipenseridae) may take up to 15 years to mature.
34
REPRODUCTIVE MODES
1. In most species of bony fishes, sperm and eggs develop in separate male and female
individuals. Males and females may look similar, or they may look very different.
Male/female differences may include size, coloration, external reproductive organs,
head characteristics, and body shape.
2. Some bony fishes are hermaphrodites: a single individual produces both sperm and
eggs.
• Sequential hermaphrodites are born one sex and change sex sometime during the
course of life. For example:
° Some damselfishes (family Pomacentridae) begin life as males and change into
females. In some, females can revert back to males.
° Some seabasses (family Serranidae) change from female to male, and are capable of
reverting back to female.
° Most wrasses (family Labridae) are born female, grow into sexually mature females,
and have the potential to transform into functional males later in life. In many of the
wrasses, sex change correlates with social hierarchy and social behavior: social
structure includes a large dominant male and many smaller, subordinate females.
Removing the male from the group triggers the largest female to begin transforming into
a male.
• Synchronous hermaphrodites have both sperm- and egg-producing organs at the
same time. In a few species, self-fertilization is possible.
3. A few species are unisexual: there is no fusion of sperm and egg. A sperm cell is
necessary to trigger an egg cell to develop, but the sperm cell ultimately degenerates
and does not contribute genetic material. The resulting young always are females.
Thus, unisexual species are entirely female. They mate with males of related species to
produce female offspring. Poecilia formosa is an example of a unisexual species.
Always female, P. formosa mates with male
P. mexicana or P. latipinna.
35
REPRODUCTIVE BEHAVIOR
1. Various factors may influence bony fish
breeding.
• Changes in the duration of sunlight (called
photoperiod) can stimulate some species of
bony fishes to begin reproduction.
• Temperature change may trigger breeding
in temperate and subpolar areas.
• Other factors that may affect reproduction
are presence of the opposite sex, currents,
tides, moon stages, and presence of
spawning areas.
2. Reproduction is generally cyclic in bony
fishes. The duration of cycles may be as
short as four weeks or as long as many
years. Some species spawn continuously
throughout the spring and summer.
• Some bony fishes may spawn many times
a year.
• Many bony fishes reproduce once a year until they die.
• Other bony fishes may reproduce only once during their lifetime. Pacific salmon (family
Salmonidae) reproduce only once during their five-year lifespan, then die soon after.
3. Diadromous fishes must have access to both marine and freshwater systems to
complete their life cycle.
FERTILIZATION AND EMBRYONIC DEVELOPMENT
1. Some species release unfertilized eggs and sperm. Young develop from eggs that
are fertilized in the water.
2. 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.
3. Oviparous bony fishes release eggs, and the developing embryo is nourished by a
yolk sac.
36
• The eggs of a bony fish generally are spherical. A soft membrane protects the egg.
Most are 0.4 to 3.0 mm (0.02-0.12 in.) in diameter.
• Some bony fishes produce and "scatter" their eggs. Some eggs drift through the water
column. Some have oil droplets that help them float. Some bottom-dwelling fishes
produce eggs that sink and remain on the ocean bottom.
• Some bony fish eggs are sticky or have tendrils that entangle them among plants and
other living or nonliving materials in the environment. In some cases parents protect
their eggs until the embryos develop and the young swim free.
• Some parents brood eggs in the mouth or on the skin, fins, or gill areas.
4. 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 embryos.
• Examples of ovoviviparous fishes are the seahorses (family Syngnathidae). In contrast
to most other animals, it's the male seahorse that incubates fertilized eggs. The female
seahorse deposits eggs into a pouch on the male's abdomen. The male releases sperm
into the pouch, fertilizing the eggs. The embryos develop within the male's pouch,
nourished by their individual yolk sacs. After the embryos have developed, the male
gives birth to tiny seahorses.
5. 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.
6. Fish larvae develop from hatched embryos. A transitional stage, larvae of many
species look and behave differently than adults. Fish larvae are free-living organisms
that feed on plankton, bacteria, or organic debris.
7. Gestation periods vary greatly among species, ranging from just a few days to
several months. Within a particular species, water temperature affects the rate at which
an embryo develops.
8. The number of offspring is inversely related to the chance a single egg has to reach
maturity and reproduce.
• In general, species whose eggs have little chance to reach maturity lay the most eggs.
The common ocean sunfish, which "scatters" unfertilized eggs, may produce more than
28,000,000 eggs in a single season. Guppies (family Poeciliidae), which mate and bear
their young live, often produce less than 25 young at a time.
• Within a species, the number of offspring a female produces varies according to many
factors including age, size, food availability, season, and water temperature.
37
PARENTAL
CARE
1. Many species
give no care to
their eggs or
young.
2. Some species
hide or guard
their eggs.
3. Some species,
such
as
the
jawfish
(family
Opisthognathidae
) brood fertilized
eggs. A male
jawfish
broods
fertilized eggs in
its mouth.
4. Some bony
fishes bear live
young that can
protect
themselves
at
birth. Very little, if
any,
parental
care is needed
after young are
released.
5. Some species
care for their
young after they
have
hatched.
Male bowfins (family Amiidae) fiercely guard their young. Some species make elaborate
nests and provide parental care to the developing fishes. Sticklebacks (family
Gasterosteidae) construct elaborate nests to care for 30 to 100 fry (juvenile fish).
LONGEVITY
1. Longevity for most bony fish species is unknown. Large species generally have a
longer life expectancy than smaller species, and colder-water species often live longer
38
than warm-water species. Some species live only for a few months. Others, like the
orange roughy (Hoplostethus atlanticus) may live for 100 years or longer.
AGING STUDIES
1. Growth rings are periodically deposited on the scales, vertebrae, and earstones of
many species of bony fishes. Experts can stain these hard body parts, examine them
for growth rings, and estimate the age of the fish.
2. Examining the scales, vertebrae, or earstones of known-age fishes after their death
enables researchers to compare the estimated age (based on growth rings) with the
fish's known age.
3. In some species, tagging and releasing fish yields information about growth rates. A
tagged fish can be measured again when it is recaptured. Researchers correlate the
measurements with the number of years since recapture and estimate a yearly growth
rate.
PREDATION
1. Depending on the species, bony fishes have a wide variety of predators, including
other fishes, birds, reptiles, amphibians, mammals (including humans), and various
invertebrates.
2. Small bony fishes may have a large variety of predators. Large bony fishes have
fewer predators.
3. Fish eggs or larvae may have different predators than adults of the same species.
Some adult fish eat fish larvae, sometimes including larvae of the same species.
4. Many bony fishes will eat members of their own species.
DISEASE
1. As in any animal population a variety of diseases can be responsible for bony fish
death. These include bacterial, viral, and fungal infections, as well as tumors.
PARASITES
1. Many types of internal and external parasites are common to bony fishes. Parasites
are not typically a cause of death.
INVASIVE SPECIES
1. A non-native species introduced into a habitat can alter the ecology of that habitat.
39
2. Some invasive species have devastating results on native species.
• A popular aquarium fish, the goldfish (Carassius auratus) is native to Asia. It has been
released - both intentionally and inadvertently - and has formed wild populations. In
some areas goldfish prey on native fish.
• A strain of Caulerpa taxifolia, a marine algae cultured for use in aquariums, is an
invasive seaweed that was inadvertently introduced into the Mediterranean Sea, where
it grows in dense beds that prevent native plants from growing, thus eliminating habitat
for native species. In 2003, experts were alarmed to find this invasive species in
California.
______________________________________________________________________
40
Activity: Fish Dissection
Duration: 2 hours
Objectives




Describe the appearance of various organs found in the fish.
Name locate and identify the organs that make up various systems of the fish
Compare and contrast fish anatomy to other dissections.
Contrast and compare a fish's body parts to a human's.
Materials












Safety goggles
dissecting pins
gloves, forceps
lab apron
scissors
paper towel
scalpel,
water
dissecting probe
preserved fish
hand lens
dissection tray.
Background
Vertebrate Classification
Kingdom Animalia
-----Phylum Chordata
----------Subphylum Vertebrata
Class
Examples
Agnatha
Jawless fishes; lamprey & hagfish
Chondrichthyes
Cartilage fish, sharks and rays
Osteichthyes
Bony fish; salmon, catfish, goldfish
Ray-finned fish are built for swimming. Instead of legs, they have fan-like parts called
FINS . Fish also have bony skulls to protect their brains. They have VERTEBRA which
protect the NERVE CORD running through them, and they have strong muscles
41
attached to their bones so they can swim well. Bony fish have a SWIM BLADDER filled
with air, which keeps them from sinking to the bottom. Many fish have SCALES, hard
plates which are part of the skin. fish have gills. GILLS are body parts which allow fish
to breathe under water. The OPERCULUM a bony flap, covers and protects the gills. All
fish are EXTOTHERMIC (ectotherms) so the inside temperature of their bodies is the
same
as
the
temperature
of
the
water
around
them.
There is oxygen in tiny bubbles throughout the water in the ocean. Fish take in this
oxygen-filled water through their mouths. The water passes over the gills. In the gills is
blood, full of tiny carbon dioxide bubbles. Because the gills are so thin, the oxygen can
go into the blood and the carbon dioxide goes out into the water. Then the water passes
out
of
the
body
of
the
fish.
Fish reproduce it is called SPAWNING. The females have soft eggs. The female fish
lays eggs in the water. The male swims over them and fertilizes them with a fluid called
MILT. Then the eggs are left to hatch on their own. Many eggs do not hatch or are
eaten by predators. Yet some survive so more fish can be born.
a. FISH PHYLUM ____________________________________________
b. CARTILAGE FISH CLASS ____________________________________
c. BONEY FISH CLASS _________________________________________
d. JAWLESS FISH CLASS _______________________________________
42
PROCEDURE
AND
OBSERVATIONS:
External features:
1. Feel the fish's skin. Why do fish have mucus.
______________________________________________________________________
Use a magnifying glass to see how the scales are arranged.
2. Why do fish have scales?______________________________________________
3. Look at the color pattern. What is the advantage of a fish being dark on dorsal
side and light on the ventral side?
______________________________________________________________________
4. Observe the lateral line. What it is used for?
______________________________________________________________________
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5. How does the lateral line works?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
6. Observe the shape of the fish. How this is an advantage?
______________________________________________________________________
7. Observe the eye. Note the relatively large size, and the large pupil, hypothesis
how important vision is for this animal?
______________________________________________________________________
8. Is there an eyelid?___________________________
9. Locate the nostrils. Describe the location and the number of the nostrils.
______________________________________________________________________
10. Insert a probe into one of the nostrils. Does the probe enter the mouth cavity?
______ Why?__________________________________________________________
11. Feel the teeth along the gum margins and on the roof of the mouth. What are the
teeth used for?______________________________________________________.
12. Determine the probable use of the tongue. Does the tongue feel like a human
tongue? __________
13. See how wide the mouth can open. Suggest a reason for this?
______________________________________________________________________
The mouth is also used for breathing. In low oxygen conditions, fish can actively pump
water
over
their
gills
by
opening
and
closing
their
mouth.
14. The gills arches can be seen by looking down the fish's mouth and gently lifting up
the operculum. Use a probe to separate the arches and explore how they are arranged.
How
many
arches
are
there_________
44
15. Place the fish on its side and look at the operculum, the boney plates which protect
the gills. Lift the operculum and look at the gills. Now cut the operculum away at its
base,
exposing
the
gills.
16. Remove the one of the gills by cutting the upper and lower attachments of the arch.
Look at the gill rakers, the bony projections along the inside curve of the arches.
Observe the large surface area provided by the gill filaments, and the thin tissue which
allows blood vessels to come into contact with the oxygen in the water. Compare and
contrast gills and lungs.
ORGAN
FUNCTION
SYSTEM
1. SCALES
2. ANTERIOR DORSAL FIN
3. NOSTRIL
4. LATERAL LINE
5. PECTORAL FIN
6. ANAL FIN
7. PELVIC FIN
8. EYE
9. OPERCULUM
10. MOUTH
11. POSTERIOR DORSAL FIN
12. CAUDAL FIN
13. ANUS
45
Label the parts on the fish.
Then find the names of these parts in the word search.
Words appear across or up and down.
46
INTERNAL ORGANS:
1. WHAT IS AN ECTOTHERM?_____________________
2. Carefully cut the fish by inserting a scissors point into the anus and open to the
bottom of the mandible (jaw). Be careful not to cut into the fish's internal organs. Cut
away the flap of skin and look for fat deposits (orange and greasy looking), which are
found around the stomach. What is the importance of fat?
______________________________________________________________________
3. Locate the swim bladder. It is made of very thin tissue and is located in the upper
body
cavity,
below
the
kidneys.
What
is
its
function?
______________________________________________________________________
4. Locate the male reproductive organs (testis) will be flaccid white or orange tissue
near the intestines. If you have a female locate the ovaries. Eggs may or may not be
noticeable in females. Both will vary in size depending on maturity of the fish. Why do
fish produce so many eggs.
______________________________________________________________________
47
5. Put the fish on its dorsal side and find the kidneys, located just under the backbone.
They are thin, dark in color, and run the whole length of the body cavity. What is their
function?
______________________________________________________________________
6. Put the probe through the mouth and into the esophagus to show the beginning of the
route. Why is the esophagus so elastic?
______________________________________________________________________
INTERNAL ANATOMY OF A FISH
7. Does the stomach have any food in it? ____________ If so make a small incision
and observe the prey. The first area of the stomach is called the cardiac stomach; this
is where digestion begins. Notice the different kinds of tissue that make up the stomach.
The pyloric stomach is that portion from which the pyloric ceca project. It begins at the
bend below the cardiac stomach, and is made of different tissue. Discuss how the
stomach area is increased by the pyloric ceca. How does this improve the function of
the stomach? __________________________________________________
8. The intestines provide the last chance to extract nutrients from food. Why is the
intestine so long? ___________________________________________. Notice the
network of blood vessels which are used for nutrient exchange. Follow the intestines to
the anal opening where waste products are eliminated.
9. The spleen will be seen by lifting the stomach. It is a reddish organ found at the end
of the cardiac stomach. What does it do?
______________________________________________________________________
10. The liver is just in front of the stomach. The liver produces bile which is stored in
the gall bladder. What does bile digest? _________________. The gall bladder is a
mass of darker tissue on the liver.
11. A fish's heart is between the gills. Identify the atrium and ventricle. How many
chambers are there ____________. The fact that the gills, heart and liver are so
close together is no coincidence. Blood pressure is best near the pump (heart). Blood is
filtered by the liver, and absorbs oxygen from the gills; both are vital functions.
12. Cut through the fish to expose the back bone and muscles. Observe arrangement of
the
muscle
masses.
(This
is
the
part
of
the
fish
we
eat.)
48
13. Observe the growth rings on the scales. Try to remove some of the scales so you
can
look
at
the
rings.
14. Explain why the fish has an inefficient heart
______________________________________________________________________
15. Dissect the brain
16. Dissect out the lens of the eye.
FILL IN THE DATA TABLE
ORGAN
FUNCTION
SYSTEM
1. HEART
2. KIDNEY
3. SWIM BLADDER
4. ANUS
5. GONADS
6. LIVER
7. BRAIN
8. VENTRICLE
9. GILLS
10. STOMACH
11. INTESTINE
12. GALL BLADDER
13. ATRIUM
14. SPINAL CORD
15. VERTEBRAE
49
Fish Anatomy
Find each of the organs below and color code them to the fish according to the key
below.
Caudal Fin (blue)
Gills (red)
Muscles (red)
Anal Fin (pink)
Heart (pink)
Vertebrae (yellow)
Dorsal Fin (yellow)
Stomach (green)
Swim Bladder (blue)
Pelvic Fin (green)
Esophagus (yellow)
Kidney (green)
Pectoral Fin (orange)
Liver (brown)
Scales (purple)
Operculum (brown)
Intestine (blue)
Lateral Line System (black)
Reproductive Organs
(orange)
50
Fish Scales Tell the Age of a Fish
Look at the image of the fish scale, like a tree, scales show rings that indicate
periods of growth. Rings that are farther apart occur when the fish grows well
and there is lots of food - in the summer season. Rings that are close
together occur when the fish does not get much food and grows slowly. On
the scale you can identify the summer growth and the winter growth. (There
will be several rings in each).
The core represents the fish when it was first born, as a fry. The rings near
the edge are the most recent periods of growth.
Color
the
summer
growth
Color the winter growth periods blue.
periods
green.
How old is this fish (in years)? _____________________
51
Answers
Fish Parts
52
53
Activity: Perch Dissection
Duration: 2 hours
Objectives

Understand the external and internal anatomy of a bony fish
Materials











Preserved perch
dissecting pan
scalpel
scissors
forceps
magnifying glass
dissecting pins
apron
gloves
eye cover
tape measure
Introduction
The fish in the class Osteichthyes have bony skeletons. There are three groups of the
bony fish --- ray-finned fish, lobe-finned fish, and the lung fish. The perch is an example
of a ray-finned fish. Its fins have spiny rays of cartilage &/or bone to support them. Fins
help the perch to move quickly through the water and steer without rolling. The perch
also has a streamline body shape that makes it well adapted for movement in the water.
All ray-finned fish have a swim bladder that gives the fish buoyancy allowing them to
sink or rise in the water. The swim bladder also regulates the concentration of gases in
the blood of the fish. Perch have powerful jaws and strong teeth for catching and eating
prey. Yellow perch are primarily bottom feeders with a slow deliberate bite. They eat
almost anything, but prefer minnows, insect larvae, plankton, and worms. Perch move
about in schools, often numbering in the hundreds.
The scientific name for the yellow perch, most often used in dissection, is Perca
flavescens (Perca means "dusky"; flavescens means "becoming gold colored"). The
sides of the yellow perch are golden yellow to brassy green with six to eight dark vertical
saddles and a white to yellow belly. Yellow perch have many small teeth, but no large
canines. Yellow perch spawn from mid-April to early May by depositing their eggs over
vegetation or the water bottom, with no care given. The eggs are laid in large gelatinous
adhesive masses.
54
Procedure (External Anatomy):
1. Obtain a perch & rinse off the excess preservative. Place the perch in your
dissecting pan.
2. Label the anterior, posterior, dorsal, and ventral sides of the perch on Figure 1.
3. Use your tape measure to determine the total length, fork length, and girth of
your fish. Record this in Table 1.
Table 1 - Fish Measurements (inches)
Total Length
Fork Length
Girth
4. Locate the 3 body regions of the perch --- head, trunk, and tail. Label these on
Figure 1.
5. Open the perch's mouth and observe its bony jaws. Locate and label the upper
jaw or maxilla and the lower jaw or mandible.
6. Feel the inside of the mouth for the teeth. Locate & label the tongue & teeth on
Figure 1.
7. Open the mouth wider and use a probe to reach back to the gill chamber.
8. Locate the nostrils and label on Figure 1.
9. Locate and note the location of the eyes. Label on Figure 1.
55
10. Find the bony covering on each side of the fish's head called the operculum. The
opercula cover & protect the gills. Label these on Figure 1.
Figure 1 - External Perch anatomy
11. Use a probe to lift the operculum and observe the gills. Note their color.
12. Use a scissors to cut away one operculum to view the gills. Find the gill slits or
spaces between the gills.
13. Use your scalpel to carefully cut out one gill. Find the cartilage support called the
gill arch and the soft gill filaments that make up each gill. Label the parts of the
gill in Figure 2.
Figure 2 - Gill Structure
56
14. Observe the different fins on the perch. Locate the pectoral, dorsal, pelvic, anal,
and caudal fins. Note whether the fin has spines. Label these on Figure 1 and
complete Table 2 on fins.
Table 2 - Fins
Name of Fin
Spines
(yes or no)
Number
Fins
of
Location
Function
15. Locate the anus on the perch anterior to the anal fin. In the female, the anus is in
front of the genital pore, and the urinary pore is located behind the genital pore.
The male has only one pore (urogenital pore) behind the anus. Determine the
sex of your perch.
16. Find the lateral line on the side of your perch. Label this line on Figure 1.
17. Use forceps to remove a few scales from your fish. Observe the scales under the
magnifying glass. Sketch a scale on Figure 3.
Figure 3 - Structure of a Scale
57
18. Count the growth rings on your scale to tell the age of your fish. (Hint: each ring
represents one year's growth.)
Procedure (Internal Anatomy):
1. Use dissecting pins to secure the fish to the dissecting pan. Use scissors to
make the cuts through skin and muscle shown in Figure 4.
Figure 4 - Cut Lines for Internal dissection
2. After making the cuts, carefully lift off the flap of skin and muscle to expose the
internal organs in the body cavity.
3. Locate the cream colored liver in the front of the body cavity. Also locate the gall
bladder between the lobes of the liver. Label these on Figure 5.
4. Remove the gall bladder & liver to observe the short esophagus attached to the
stomach. Label the stomach on Figure 5
5. At the posterior end of the stomach are the coiled intestines. Locate and then
label these on Figure 5.
6. Find the small reddish brown spleen near the stomach and label this on Figure 5.
7. Below the operculum, are the bony gill rakers. Locate these & them label them
on Figure 5.
8. In front of the liver & behind the gill rakers is the pericardial cavity containing the
heart. The heart of a fish only has 2 chambers --- an atrium & and a ventricle.
Locate the heart & label it on Figure 5.
9. In the upper part of the body below the lateral line is the swim bladder. This sac
has a thin wall and gives the fish buoyancy. Label the swim bladder on Figure 5.
10. Below the swim bladder are the gonads, testes or ovaries. In a female, these
may be filled with eggs. Label the gonads on Figure 5.
11. Find the 2 long, dark kidneys in the posterior end of the perch. These filter
wastes from the blood. Label the kidneys in Figure 5.
12. Wastes exit the body through the vent located on the ventral side of the perch.
Label this structure on figure 5.
58
Figure 5 - Internal Perch Anatomy
Questions & Observations:
1. Are both jaws of the fish equally movable? Explain your answer.
2. Does the perch have eyelids?
3. How many gills are located on each side of the perch? What covering protects them?
4. What is the function of the gill rakers?
5. Explain how gas exchange occurs at the gills.
6. Which fin was the largest? What other difference do you notice in this fin when it was
compared to the others?
7. What was the sex of your fish?
8. What is the function of the lateral line?
9. Describe how the scales are arranged on the trunk & tail of your fish.
10. Explain how the swim bladder controls buoyancy.
______________________________________________________________________
59
Resources
http://users.tamuk.edu/kfjab02/Biology/Vertebrate%20Zoology/b3405_ch06.htm
http://www.savalli.us/BIO370/Diversity/02.Agnatha.html
http://www.treasuresofthesea.org.nz/jawless-fishes-and-bony-fishes
http://www.seaworld.org/animal-info/info-books/bony-fish/index.htm
http://cas.bellarmine.edu/tietjen/images/bony_fish.htm
http://www.gma.org/fogm/Osteicthyes.htm
http://dj003.k12.sd.us/science%20labs/dissection/fish%20dissection.htm
http://chs.cusd.claremont.edu/~rhoyle/mm/Course%20Assets/Marine%20Biology/Labs/p
df%20-%20Fish%20Dissection.pdf
http://www.biologyjunction.com/perch_dissection2.htm
http://www.valleycity.k12.nd.us/jrsrhigh/jrsrstaff/jrsrstffpgs/rt/Biology/BiologyLab/39lab.pdf
60