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[Inc._Encyclopaedia_Britannica]_Britannica Illustrated Science Library -FISH AND AMPHIBIANS

[Inc._Encyclopaedia_Britannica]_Britannica Illustrated Science Library -FISH AND AMPHIBIANS

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FISH
AND AMPHIBIANS

Britannica Illustrated Science Library

Encyclopædia Britannica, Inc.
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Britannica Illustrated Encyclopædia Britannica, Inc.
Science Library Jacob E. Safra, Chairman of the Board
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© 2008 Editorial Sol 90 Michael Ross, Senior Vice President, Corporate Development
All rights reserved. Dale H. Hoiberg, Senior Vice President and Editor
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Idea and Concept of This Work: Editorial Sol 90
International Standard Book Number (set):
Project Management: Fabián Cassan 978-1-59339-797-5

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Illustrators: Guido Arroyo, Pablo Aschei, Gustavo J. Caironi, Britannica Illustrated Science Library:
Hernán Cañellas, Leonardo César, José Luis Corsetti, Vanina Fish and Amphibians 2008
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Fish and Amphibians

Contents

General
Characteristics

Page 6

Life in
the Water

Page 18

Diversity

Page 38

Amphibians

Page 60

People, Fish,
and Amphibians

Page 80



VIETNAM Water, the
Along this country's nearly Source of Life
200 miles (300 km) of
coastline live great T he life of marine creatures is
numbers of people who fascinating and has always been
depend on fishing and closely linked to human life. This is so
coral reefs for their particularly because fishing has been the
livelihood. livelihood of islanders through the years.
Yet for some time, in many areas of the
world—such as Nha Trang Bay, on the
south coast of Vietnam—this activity has

been in a state of crisis. In Nha Trang Bay this reason, they have developed various
the growth of outside investment in survival techniques to live in such a wide
aquaculture has limited the economic variety of places.
opportunities of the local population,
including fishing for squid and other D espite the fact that lunglike sacs
species in the reefs with hook and line. evolved because of the difficulty of
In other cases, commercial fishing breathing with gills in water with low
endangers the future of those who rely on oxygen content, the development of these
traditional fishing methods to make a sacs was also the first step toward moving
living. This is only one of the topics onto land. Some descendants of the first fish
explored in this book, which also relates in with fleshy, jointed fins, known as lobe-fin
detail many secrets of these vertebrates, fishes, began to find terrestrial food sources
which were among the first creatures with and, with time, adapted more completely to
skeletons to appear on the Earth. Perhaps life on the planet's surface. This evolutionary
knowing more about their habits and change—passing from an aquatic to a
modes of life may move us to care for terrestrial medium—constituted a true
them and protect them. They are at the revolution for the life-forms that existed up
mercy of variations in water conditions to until then. The amphibians we will show you
a greater extent than humans. in this book that are living today are a tiny
representation of all those that appeared
H umans have marveled for centuries at during the Devonian Period, most of which
the fact that, after journeying across became extinct during the Triassic Period.
the ocean, salmon can find the river
where they were born. Is this navigational A mphibians, especially some frog
ability related to the Earth's magnetic field, species, have become true specialists
sense of smell, instinct, or something else in the art of mimicry. One of the most
that humans cannot even imagine? For those fascinating examples is the European tree
interested in statistics, in the Yukon River in frog, which changes color to regulate its
Alaska and in Canada, certain tagged body temperature. On warm, dry evenings
Chinook salmon covered nearly 2,000 miles the frog rests in sunny places, and its skin is
(3,200 km) in 60 days. Upon entering the pale. As its surroundings become cooler, the
river, the salmon stop eating and utilize the frog darkens to absorb heat. Although
fat they accumulated while in the ocean. amphibians are masters of camouflage,
which protects them from predators, at
After laying their eggs, many of the present they are the object of worldwide
females die. Most ocean fish seek shallow, concern because of the dramatic decline in
nutrient-rich waters in which to lay their their populations. Turn the page, and you will
eggs. That is why coastal waters and discover much more about the abilities of
estuaries are so important to the life cycle of fish and amphibians, extraordinary creatures
many species. Another oddity of these that live right next to us.
animals is that they have adapted to living in
a variety of aquatic habitats: rivers, lakes,
estuaries, coral reefs, and the open sea. For

General Characteristics

F ish were the first vertebrates fish, the earliest fish had no scales, fins,
with bony skeletons to appear or jawbone, but they did have a type of
on the Earth. They doubtless dorsal fin. Over time they have been
form the most numerous group changing in form and size to adapt to
of vertebrates. Unlike today's different environments, in both fresh

CROCODILE FISH FIN EARLIEST FORMS 8-9 CARTILAGINOUS FISH 14-15
This fish, which lives in DISTINGUISHING FEATURES 10-11 ANATOMY 16-17
waters with abundant coral BONY FISH 12-13
reefs, can grow up to 21
inches (54 cm) long.

water and salt water. Their bodies are these complex creatures normally
generally streamlined, being covered breathe through gills that capture
with smooth scales and having fins that oxygen dissolved in the water, and they
enable them to move with energy, are cold-blooded.
direction, and stability. In place of lungs,

8 GENERAL CHARACTERISTICS

Earliest Forms

A bout 470 million years ago, the first fish appeared. Unlike today's
fish, they did not have a jawbone, fins, or scales. Hard plates
covered the front part of the fish and formed a protective shield.
They also had a solid, flexible dorsal spine that allowed them to propel
themselves. Later, in the Silurian Period, fish appeared that had a
jawbone. Known as the gnathostomata, they were large predators.

Pteraspis CONICAL NOSE EYES
Its streamlined shape Very small,
The fish without a jawbone, helped the fish move. located on both
Pteraspis, was about 6.5 sides of the head.
inches (16 cm) long and lived in
the seas of Europe, Asia, and North
America. These fish were most
abundant during the Devonian Period.
They had bodies with armor that
covered their heads, and they had a
streamlined shape. The shell had a co-
nical nose that helped the fish to move.

6.5 inches (16 cm) MOUTH
Having no jawbone,
WING SHIELD they fed on small
Scientific Pteraspis organisms.
name
Diet Small organisms cranium
Habitat Sea, then rivers and lakes The evolution of the jawbone
Range Europe, Asia, North America modified the configuration
Period Early Devonian of the skull.

EVOLUTION OF THE JAWBONE

The development of the jawbone was a
long evolutionary process that involved
changes in the diet of fish to include not
only small organisms but also other fish.

1 PRIMITIVE
VERTEBRATE
Marine
The first fish lamprey

had no jawbone. Placoderms Fossil

2 ELASMOBRANCHIMORPH Modern fish Fish with lungs appeared
The formation of the in the Mesozoic Era
(200 million years ago).
jawbone permitted new Similar to amphibians, these
species breathe with lungs
feeding habits, and the and are now considered
living fossils. The line
fish evolved from through the center of the
photo of the fossil is the
herbivore to carnivore. fish's lateral line.

3 BONY FISH FOSSILIZED
They already had a LUNGFISH SCALES
Dipterus valenciennesi
specialized jawbone

like fish of today.

FISH AND AMPHIBIANS 9

Dunkleosteus Its head was Dorsal The tail was not
protected by fin protected by
The Arthrodira—with a jointed strong armor. scales.
neck—were armored fish that
STREAMLINED SHAPE predominated in the late Devonian This area of the body
The shape of Pteraspis Period. The Devonian predator had neither armor
shows that it was an Dunkleosteus was an arthrodiran nor scales.
excellent swimmer. placoderm that lived over 300 million
years ago. Its head was encased in It had a lobed tail, similar
an impressive set of plates 1.2 inches to a shark's tail, which
(3 cm) thick, with razor-sharp bony indicates that it was a
plates that served as teeth. powerful swimmer.

DORSAL SPIKE FIERCE JAW
Located on the fish's
back, it worked like a Dunkleosteus was a
dorsal fin.
fierce predator that

devoured any type of

prey, including sharks.

It also had strong
jaws with bony teeth.

DORSAL SPINES
These helped the fish
to stay balanced while
swimming.

16 feet

(5 m)

LENGTH OF THE FISH

TAIL
The shape of the tail
helped balance the
weight of the armor.

LATERAL LINE
Sensory organs are
present on both sides
of the body and on top
of the armor.

Chimaeriformes Cheirolepis Pycnodus Sole

Evolution Holocephali Cheirolepididae Pycnodontiformes Holostei Teleostei

In the Devonian Period Wing shield Dunkleosteus Sharks and rays Eusthenopteron Chondrostei NEOPTERYGII
ocean fish began to (Pteraspis)
diversify. Coelacanths appeared,
as well as the earliest bony fish Placoderms Elasmobranchii Sarcopterygii
and the first cartilaginous fish,
including sharks. In this period Lamprey Acanthodii ACTINOPTERYGII
the three main groups of Jawless CARTILAGINOUS FISH
gnathostomad fish also DevonianBONY FISH
appeared: the placoderms, fish GNATHOSTOMATA
chondrichthyes, and THIS PERIOD SAW AN EXPLOSION IN
osteichthyes. VERTEBRATA THE DIVERSITY OF FISH SPECIES.

10 GENERAL CHARACTERISTICS

Distinguishing Features

S imilar characteristics define nearly all fish, with a few rare exceptions. These aquatic
animals are designed to live underwater, and they have a jawbone and lidless eyes and are
cold-blooded. They breathe through gills and are vertebrates—that is, they have a spinal
column. They live in the oceans, from the poles to the equator, as well as in bodies of
fresh water and in streams. Some fish migrate, but very few can pass from salt
water to fresh water or vice versa. Their fins enable them to swim and move
in different directions. Animals such as dolphins, seals, and whales are
at times mistaken for fish, but they are actually mammals.

EYES HEAD PECTORAL FIN ANTERIOR
On the side of the One of the three Symmetrical, relatively small, DORSAL FIN
head, protected by main divisions of and with a radial structure This fin has stiff
fatty membranes its body rays and has a
stabilizing
function.

NASAL PITS
Also called
nares; lie on
either side of
the head

MOUTH
The angle of the mouth
affects what the fish
can eat.

OPERCULUM GILLS PELVIC FINS
A bony flap that covers The fish's These permit the fish
the gills and helps breathing organs to swim upward and
regulate water flow downward.

Gill Breathing Filaments Oxygenated Water flow
blood
Gills are the organs that fish Gill raker
use to breathe. They are made
of filaments linked by the gill arches. Opening at Capillary
The fish uses its gills to take in edge of the tubes
oxygen dissolved in the water. operculum
Through a process known as diffusion, Blood
oxygen is transferred to the blood, flow
which has a lower concentration of
oxygen than the water. In this way Gill arch
the fish oxygenates its blood,
which then circulates to the rest of Gill filament Deoxygenated Filaments
its body. In most bony fish blood
(osteichthyes) water flows in through
the mouth, splits into two streams,
and exits through the gill slits.

Near- POSTERIOR FISH AND AMPHIBIANS 11
fossils DORSAL FIN
This soft-structured Jawless Fish
Choanichthyes fin is located
(Sarcopterygii) are archaic between the dorsal Of the ancient agnathans, considered
bony fish with fleshy fins. fin and the tail. the first living vertebrates, only
Some of them were the first lampreys and hagfish are left.
animals with lungs. Only a
few species survive. SEA LAMPREY
Lampetra sp.
COELACANTH
Latimeria chalumnae Its round, toothed mouth
allows it to suck the blood of
This species was thought fish of various species. There
to have gone extinct are also freshwater lampreys.
millions of years ago,
until one was discovered Just Cartilage
alive off the coast of South
Africa in 1938; more of Cartilaginous fish, such as rays and
these fish were found later. sharks, have extremely flexible
skeletons with little or no bone.
SCALES
The scales are RAY
imbricateΩthat Raja miraletus
is, they overlap
one another. Its large fins send
currents of water
carrying plankton and
small fish to its mouth.
The ray is very fast.

LATERAL LINE
Fish have sensory organs
all along this line.

ANAL FIN TAIL MUSCLE CAUDAL FIN With Spines
Soft, with a row This is the It moves from side
of finlets strongest muscle to side, propelling Osteichthyes is the most numerous
in the fish. the fish forward. class of fish. The skeleton has some
In Action level of calcification.
Water Open Water Closed
Water enters the mouth and mouth mouth ATLANTIC MACKEREL
flows over the gills. After the gills Scomber scombrus
extract oxygen, the water is Pharynx
expelled through the gill slits. This fish has no teeth. It lives in
Esophagus Gills Open temperate waters, and its meat is
Operculum operculum considered delicious. It can live
Closed
Opens and closes the operculum for more than 10 years.
openings where water exits
25,000

Is the number of known fish
species, making up nearly one
half of all chordate species.

12 GENERAL CHARACTERISTICS

Bony Fish

T he group of fish that have evolved and diversified most in the
last few million years are the osteichthyes, fish with spines
and jawbones. In general, their skeletons are relatively
small but firm, being made mostly of bone. Flexible fins enable
them to control their movements with precision. The various
species of osteichthyes have adapted to a wide variety of
environments and even to extreme conditions.

Solid Structure

The skeleton of a bony fish is divided into the cranium,
spinal column, and fins. The opercula, which cover their
gills, are also made of bone. The cranium holds the brain
and supports the jawbone and gill arches. The vertebrae
of the spine are jointed; they provide support to
the body and join the ribs at the abdomen.

UPPER LACRIMAL
JAW BONE

CRANIUM

LOWER EYE OPERCULAR CLAVICLE PECTORAL
JAW SOCKET BONES FIN
protect
PERCH the gills. PELVIC
FIN
Perca fluviatilis PERCH SCALES
The skeleton, along with the They overlap CYCLOID
bony structure of the fins Perca fluviatilis and are
covered with
Actinopterygii mucus. CTENOID
GANOID
The main characteristic of
actinopterygian fish is their bony
skeleton, with bony spines in their
fins. They have a cartilaginous skull
(partly calcified) and only one
pair of gill openings
covered by an
operculum.

THERE ARE
OVER

480

FAMILIES

FISH AND AMPHIBIANS 13

OCEAN SUNFISH The Swim Bladder

Mola mola An appendage of the intestines that regulates flotation by filling with and
The largest osteichthian emptying itself of gas. The gas enters through a gland that extracts the
fish, it can grow to be gas from a net of capillaries, called the rete mirabile, and it leaves the
11 feet (3.3 m) long and bladder through a valve that causes it to dissolve back into the blood.
can weigh 4,000
pounds (1,900 kg). EMPTY FULL
When the fish empties its By reducing its
swim bladder, it sinks. density, the fish rises.

Rete Dorsal
Mirabile Aorta

FIRST SECOND
DORSAL FIN DORSAL FIN

RIB Gas SWIM
Gland BLADDER
INTERHEMAL
(VENTRAL) SPINES VERTEBRAL VERTEBRA
support the spiny rays of COLUMN Neural spine
the anal fin. The main nerves
and blood vessels Neural arch
Sarcopterygii run above and
below the bony Centrum
Another name for the Choanichthyes, center of the spine.
a subclass of bony fish. Their fins, like Hemal arch
the fins of whales, are joined to the body CAUDAL FIN (chevron)
by means of fleshy lobes. In lungfish, VERTEBRAE Hemal spine
these lobed fins look like filaments.
SPINY RAYS
OF ANAL FIN

CAUDAL FIN
propels the fish
through the water.

COELACANTH

Latimeria chalumnae

DETAIL OF
FLESHY FIN

14 GENERAL CHARACTERISTICS

Cartilaginous

A s indicated by the name, the skeleton of cartilaginous fish is made of cartilage,
a flexible, durable substance that is softer than bone. They have jaws and
teeth, which are usually hard and sharp. Their body is covered with hard scales.
However, they lack a characteristic shared by most bony fish—the swim bladder, an
organ that helps fish to float. Their pectoral fins, tail, and flat head
give this group a streamlined profile.

Sharks 2,650 LIGHT AND
pounds FLEXIBLE
These fish live in tropical waters, The skeleton is
although some do inhabit (1.2 metric tons) very flexible, but
temperate waters or fresh the spinal column of
water. They have an elongated, NORMAL WEIGHT OF A SHARK cartilage is firm, with
cylindrical shape and a pointed (SUPERORDER SELACHIMORPHA) mineral deposits.
snout, with the mouth on the
underside. Each side of their SPINAL
head has five to seven gill slits. COLUMN

BLOOD Nostril
They are
cold-blooded.

Heat- Surface SHARP TEETH
generating pore The teeth are
muscles triangular in shape.
Epidermis All chondrichthyes
lose their teeth
Sensory cells and grow
new ones.

Nerves Gelatinous tract

ACUTE SENSES AMPULLAE OF
Chondrichthyes have LORENZINI
ampullae of Lorenzini, detect electric
acutely sensitive lateral signals transmitted
lines, and a highly by potential prey.
developed sense of smell.

Primitive Manta Rays
and Skates
The ancient origin of
Chondrichthyes contrasts These fish have two pectoral fins joined on
sharply with their highly the front of the body. They use them to
evolved senses. This is a swim, giving the impression that they fly
fossilized cartilage vertebra in the water. The rest of the body moves
of a shark from the Paleozoic similarly to a whip. Their eyes are located
Era, between 245 and 540 on the upper side of the body; the mouth
million years ago. It was and gills are on the lower side.
found in a fossil deposit in
Kent, England. The blood of RAY Rays may have five or
sharks has a high six rows of gills;
concentration of urea, which is Raja clavata (Thornback Ray) chimaeras have only one.
presumed to be an adaptation to This species lives in cold oceans in
salt water and constitutes a depths up to 660 feet (200 m).
fundamental difference between sharks
and their freshwater ancestors.

FISH AND AMPHIBIANS 15

SCALES HOW IT REPRODUCES
Most of these fish The modified pelvic fin
have skin with of the male is its sexual
thousands of organ. The fin penetrates
interlocking scales, the female, which then
called denticles or lays a string of eggs. The
placoid scales. young are not born in
larval form.

IN SOME SHARK SPECIES, THE YOUNG
DEVELOP WITHIN THE FEMALE, INSIDE A
STRUCTURE SIMILAR TO A PLACENTA.

GILL SLITS HETEROCERCAL TAIL
These life-forms The shark's caudal fin is
small, and the upper
may have five or lobe is larger than the
lower lobe.
six gill slits.

SHARK

Superorder
Selachimorpha

This X-ray shows the
spine and nerves.

Chimaerae

Deepwater fish. Like the prehistoric animals, they have
large heads and pectoral fins. They have a spine in front
of the first dorsal fin. The back end of the body

narrows into a tail followed by a
thin filament.

CHIMAERAS

Rhinochimaera
pacifica
This fish lives in
the dark at depths
of up to 4,900 feet
(1,500 m); it is 4
feet (1.2 m) long.

16 GENERAL CHARACTERISTICS SIMPLE EYE BRAIN
Each eye focuses to one side; receives information
Anatomy there is no binocular vision. and coordinates all
the fish's actions
M ost fish have the same internal organs as amphibians, Suspensory Retina and functions.
reptiles, birds, and mammals. The skeleton acts as a ligament
support, and the brain receives information through Lens Optic
the eyes and the lateral line to coordinate the motions of the nerve
muscles in propelling the fish through the water. Fish breathe Iris
with gills, they have a digestive system designed to
transform food into nutrients, and they have a heart that
pumps blood through a network of blood vessels.

Cyclostomata 45 THE CURRENT
NUMBER OF SPECIES
Its digestive tract is little more than OF CYCLOSTOMATA MOUTH GILLS
Structures
a straight tube extending from its with multiple
folds that
round, jawless mouth to the anus. provide oxygen HEART
to the blood receives all
Because of their simplicity, the blood and
pumps it toward
many species of lampreys the gills. LIVER

are parasites. They live CAUDAL EYE
off the blood of other FIN
fish and have thin BREATHING
SACS
pharyngeal

sacs instead ANUS
of gills.

HEART

LIVER FIRST
DORSAL
FIN

TOOTHED
MOUTH

LAMPREY INTESTINE

Lampetra sp.

SUPPORT FOR NOTOCHORD
PHARYNGEAL SACS TESTICLES

VERTEBRAE

STOMACH BRAIN

RIGHT
KIDNEY

GONAD

Chondrichthyes NASAL PIT

A shark has the same organic SHARK MOUTH GILL HEART LIVER STOMACH
structures as a bony fish, except for SLITS
the swim bladder. A shark also has a Carcharodon sp.
corkscrew-like structure called a spiral
valve at the end of its intestine to
increase the surface area for
absorption of nutrients.

FISH AND AMPHIBIANS 17

SPINAL CORD DORSAL DORSAL MUSCULATURE 10 THE SURFACE AREA OF THE GILLS
FIN AORTA is concentrated IS 10 TIMES THE SURFACE AREA
around the spinal OF THE REST OF THE FISH.
column and the tail.

LATERAL LINE CAUDAL FIN
has sensitive is divided into
receptors that symmetrical
are connected lobes.
to the brain.

BROWN
TROUT

Salmo fario

STOMACH SWIM BLADDER ANUS ANAL
INTESTINE A gland fills it with gas An opening for the FIN
and empties it to regulate expulsion of feces, urine,
swimming altitude. and reproductive fluid

Osteichthyes REGULATION OF SALINITY

Typically, their organs are FRESHWATER FISH Salt SALTWATER FISH Water Water outlet
compressed in the lower front Freshwater fish run absorption These fish intake
quarter of the body. The rest of constantly absorb
their internal structure consists the risk of losing salt Elimination of salt water to
mainly of the muscles that the to their environment. water in urine replenish the water
fish uses to swim. Some bony in their bodies, but
fish, such as carp, have no They drink only a Water intake they must eliminate Excretion of salts Excretion of salts
stomach but rather a tightly small quantity of excess salt from the through the gills through urine
coiled intestine. water, and they marine environment.
obtain additional salt
from their food.

INTESTINE SPERM SEMINAL MUSCLE
CONDUITS VESICLE SEGMENTS
DORSAL
AORTA RECTAL SECOND UPPER
GLAND DORSAL FIN CAUDAL LOBE

620

KNOWN SPECIES OF

CHONDRICHTHYES

PECTORAL SPIRAL CLOACA KIDNEY ANAL LOWER
FIN VALVE FIN CAUDAL
LOBE

Life in the Water

T he idea that fish are blind is camouflage themselves or defend their
wrong. Most fish have the best territory. Most fish can vary their
possible eyesight for their coloring when something changes in
habitat. Further, they can see in their environment. Silverfish, common in
color and use colors to all freshwater habitats, have dark backs

GLOBEFISH PROTECTIVE LAYER 20-21 YOU ARE WHAT YOU EAT 30-31
When threatened, this strange EXTREMITIES 22-23 LIFE CYCLE 32-33
animal reacts by swallowing THE ART OF SWIMMING 24-25 MATTERS OF LIFE AND DEATH 34-35
water until it blows up like a WONDERS OF COLOR 26-27 THE BEST DISGUISE 36-37
balloon. ASSORTMENT OF SHAPES 28-29

(ranging from greenish brown to dark the crystalline blue of lakes. Seen from
blue), but the sides of their bellies are below, the lower part becomes confused
silvery white. When viewed from above, with bright reflections in the water.
their backs become confused with the
deep hues of the river water or even with

20 LIFE IN THE WATER

Protective Layer FOSSILIZED SCALES

M ost fish are covered with scales, an external layer The remains of these thick, shiny, enameled
of transparent plates. All fish of a given species have scales belong to the extinct genus Lepidotes,
the same number of scales. Depending on the family and a fish that lived during the Mesozoic Era.
genus of a fish, its scales can have a variety of characteristics.
Scales on the lateral line of the body have small orifices that link
the surface with a series of sensory cells and nerve endings. It is
also possible to determine a fish's age by studying its scales.

Rhomboid
shield

SCALE REGENERATION Original Internal
Scales grow back after scales filament
a lesion, but the new
ones are different from
the original scales.

External
focus

Internal
radius

Protuberance EDGES
are overlapping,
Base with a smooth
texture.
TOOTHED
SCALE
With enamel

BLUE SHARK BASAL PLATE
Prionace glauca A smooth,
enameled surface

Placoid Scales

Typical of cartilaginous fish and other ancient
species, these scales are made of pulp, dentine,
and enamel, similar to the composition of teeth,
and they have small extensions. The scales are
usually very small and extend outward.

FISH AND AMPHIBIANS 21

Focus EPIDERMIS
With protective
Toothed mucus
spokes
TOOTHED EDGES
EPIDERMIS provide roughness.
covers most of the
body. Ctenoid scales

CUTICLE SHIELDS These scales overlap like tiles on a roof,
has a mucous The sturgeon has the same as cycloid scales. Another
consistency. five rows of these. very common type of scale among
bony fish, they are rough, having small
Cycloid scales Ganoid scales extensions that look like combs.

One of the most common types of scales Rhomboid in shape, these scales are interwoven PERCH
among bony fish, the cycloid scales are and connected with fibers. The name comes from Perca sp.
organized so that the exposed surfaces their outer covering, which is a layer of ganoin, a
overlap, forming a smooth and flexible cover. type of shiny enamel. Sturgeon and pipefish have AGE BY SCALES
They are round with a soft, exposed surface, scales of this type.
such as those of carps and silversides. A fish does not add new scales as it
STURGEON grows, but the scales it has increase
Acipenser sturio in size. In this way growth rings are
formed, and the rings reveal the age
DISTRIBUTION OF SCALES of the specimen.

Most scales occur in rows that slant diagonally Winter
downward and back. Species can be accurately growth line
identified by the number of rows (as counted
along the lateral line), among other Summer
characteristics. growth line

Transverse Exposed
line area

Lateral
line

SALMON
Family Salmonidae

RED SNAPPER
Lutjanus campechanus

22 LIFE IN THE WATER

Extremities

A fish can control its motion, direction, and stability by means of its
fins and tail. Anatomically these are extensions of the skin beyond the
body and, in most bony fish, are supported by rays. The fins reveal
much about the life of each fish. Thin fins with a split tail indicate that the
animal moves very quickly, or it may need them to cover great distances.
On the other hand, fish that live among rocks and reefs near the ocean
floor have broad lateral fins and large tails.

SIAMESE FIN RAYS
FIGHTING FISH Bony filaments
Betta splendens that are joined by
spreads its fins like a membrane
a fan when it jumps.

The highest Homocercal Tail
and longest
lobe turns The caudal fin is divided into two equal lobes,
upward. an upper and a lower lobe, which extend from
the end of the spinal column.
GREY REEF SHARK
Carcharhinus amblyrhynchos The spinal column
The heterocercal tail is typical ends in a broadened
of these cartilaginous fish, as
well as of sturgeons. structure.

Heterocercal Tail 1/8 The proportion of the length of a salmon's
homocercal tail with respect to its body.
Its two lobes are uneven. The dorsal spine turns
upward in the highest lobe, and the rays that The Typical Tail
form the two lobes of the caudal fin extend
from the lower end of the spinal column. The vast majority of bony fish have homocercal tails.

The shark's spine extends into
the upper lobe of the caudal fin.

1/3 The proportion of the lower lobe of The lower lobe is
the tail to the upper lobe of the tail smaller and is merely a
projection to the side
of the spine.

FISH AND AMPHIBIANS 23

An Integrated Team Dorsal Tuna's adipose Caudal
finΩstabilizing finΩno known finΩpropelling
In general, fish have seven fins: three single function function function
fins (dorsal, caudal, and anal) and two sets
of paired fins (pelvic and pectoral). Each fin has The ventral fins Pectoral fins joined Anal finΩtogether with
specific functions related to the fish's movement. function like to the skullΩused the dorsal fin, works as
In all bony fish, the fins are made of bony rays hydroplanes. for swimming a steering device.
and not of flesh. Tuna and a few other fish have
one extra fin between the dorsal and caudal fins. GOLDFISH
Their thin lateral fins indicate that they can swim Carassius auratus
at high speeds. Others, such as the roosterfish Bright and colorful, highly
(Nematistius pectoralis), have huge dorsal and prized by aquariums
ventral fins, and their main function is different:
they are used to scare off potential predators.

GOLDFISH HALF-MOON
Carassius auratus SHAPE
A species bred for its To provide
beauty. Its tail can have speed
eight different shapes.

SALMON
Salmo genus
Large dorsal and anal
fins with pointed ends

AFRICAN LUNGFISH
Protopterus annectens
There are four extant species of
this fish and few specimens, but
they proliferated during the
Devonian Period.

FILAMENTS
Short and
symmetrical above
and below

Diphycercal Tail

This kind of tail ends in a point; the spinal
column reaches to the end, and the tail is
surrounded above and below by a soft
caudal fin. This very rare form is found
on some sharks and hakes and in
archaic bony fish.

The dorsal spine extends
to the tip of the fin.

1/4 The length of the tail
in relation to the rest
of the body

24 LIFE IN THE WATER UPSIDE-DOWN
CATFISH
The Art of Swimming Synodontis nigriventris
This fish swims upside down,
T o swim, fish move in three dimensions: forward and back, left seeking food sources that are
and right, and up and down. The main control surfaces that fish less accessible to other species.
use for maneuvering are the fins, including the tail, or caudal fin. To
change direction, the fish tilts the control surfaces at an angle to the water Red muscles are for slow
current. The fish must also keep its balance in the water; it accomplishes or regular movements.
this by moving its paired and unpaired fins.
Larger white muscles are
MUSCLES GREAT WHITE SHARK for moving with speed, but
Carcharodon carcharias they tire easily.
The tail has powerful muscles that
enable it to move like an oar. In its side-to-side
movement, the tail
1 The crest of the body's wave displaces the water.
moves from back to front.
Starting Out

The movement of a fish through the
water is like that of a slithering snake.
Its body goes through a series of
wavelike movements similar to an S
curve. This process begins when the
fish moves its head slightly from
side to side.

At first the STREAMLINED SHAPE The head
tail is even moves from
with the head. Like the keel of a ship, the rounded contours of a fish side to side.
are instrumental. In addition, most of a fish's volume
is in the front part of its body. As the fish swims
forward, its shape causes the density of the water
ahead to be reduced relative to the density of the
water behind. This reduces the water's resistance.

THE FISH'S KEEL THE FASTEST The powerful caudal The unfurled dorsal
fin displaces large fin can be up to 150
A ship has a heavy keel in the SAILFISH amounts of water. percent of the width
lower part to keep it from Istiophorus of the fish's body.
capsizing. Fish, on the other hand, platypterus
have the keel on top. If the paired
fins stop functioning to keep the
fish balanced, the fish turns over
because its heaviest part tends to
sink, which happens when fish die.

KEEL LIVE DEAD 70 miles per hour (109 km/h) Its long upper jaw
FISH FISH enables it to slice
The maximum swimming speed it attains through the water,
aiding this fish's
hydrodynamics.

FISH AND AMPHIBIANS 25

Forward The Upward and
Motion dorsal fin Downward
keeps the
results from the fish The angle of the fins relative to the body allows
synchronized S- upright. the fish to move up or down. The paired fins,
curve movement of located in front of the center of gravity, are used
the muscles The pectoral for this upward or downward movement.
surrounding the fins maintain
spinal column. These balance and Ascent
muscles usually make can act as
alternating lateral brakes.
motions. Fish with large
pectoral fins use them like The ventral fins Paired Descent
oars for propulsion. stabilize the fish fins
for proper balance.
The oarlike movement
of the tail is the main Balance
force used for forward
motion. When the fish is moving slowly or is still in
the water, the fins can be seen making small
2 movements to keep the body in balance.

Forceful Stroke When the crest 3 1 second
reaches the area
Muscles on both sides of the spinal column, between the two Complete The amount of time it takes for this
especially the tail muscles, contract in an dorsal fins, the tail Cycle shark to complete one swimming cycle
alternating pattern. These contractions fin begins its push
power the wavelike movement that propels to the right. When the tail moves back
the fish forward. The crest of the wave toward the other side and
reaches the pelvic and dorsal fins. reaches the far right, the head
will once again turn to the
The crest of the right to begin a new cycle.
wave passes to the
first dorsal fins. CAT SHARK
Scyliorhinus sp.

The resulting
impulse moves
the fish
forward.

School The fish on the outside,
guided by those in the
A group of fish, usually of the same middle, are in charge of
species, that swim together in a keeping the group safe.
coordinated manner and with
Swimming in Groups specific individual roles The fish in
the middle
Only bony fish can swim in highly 1cubic mile control the
coordinated groups. Schools of fish school.
include thousands of individuals that (4 cu km)
move harmoniously as if they were a
single fish. To coordinate their motion The area that can be taken up by
they use their sight, hearing, and lateral a school of herring
line senses. Swimming in groups has its
advantages: it is harder to be caught by a
predator, and it is easier to find
companions or food.

26 LIFE IN THE WATER

Wonders of Color

F ish use color to communicate with others of their species.
They also use color in mating rituals and even to hide from
their prey. A young emperor angelfish has blue and white
spirals, but it develops its own appearance when it reaches
maturity. This helps it to find a mate and define its territory.
Today science is discovering how fish perceive differences of
color and what sort of messages the colors convey.

EMPEROR ANGELFISH
Pomacanthus imperator

This fish comes in various sizes and colors.
It also changes shades as it matures. Its white
stripes on a blue background form concentric
rings, and they grow just enough to give
the adult fish magnificent horizontal
yellow stripes.

SIAMESE FIGHTING FISH
Betta splendens

One of the most popular freshwater
species. Only the males exhibit a wide
variety of colors—red, green, blue, and
purple—which they obviously use as a
form of seduction.

PERCULA CLOWNFISH OCELLARIS CLOWNFISH
Amphiprion percula Amphiprion ocellaris

The clownfish is known for This fish has an orange body with two white
its intense red, orange, and bands. It lives in coral reefs from Sri Lanka
white colors. It lives among to the Philippines and north of Australia.
anemones, a predator species
that affords it protection from
possible attackers.

HUMPBACK GROUPER WRASSE
Cromileptes altivelis Bodianus sp.

This fish is found in southeast Asia, and This fish's showy colors repel potential
its meat is considered a delicacy by predators, with the
gourmets. It lives in caves as a means of contrasting tones
serving as a
defense from predators. warning.

CLOWN TRIGGERFISH GOLDFISH
Balistoides conspicillum Carassius auratus
Half of its body is black with large white This adaptable fish is the
spots, and the other half is nearly all black, most popular for aquariums.
with a group of strange black shapes with Its highly developed sense of
a yellow border. Its bright orange lips look smell is important in its
like those of a clown. search for mates and food.

WHITETAIL THREADFIN BUTTERFLY FISH
DAMSELFISH Chaetodon auriga
Dascyllus aruanus A dark band covers each eye,
With its white body and a black eye-shaped spot on
and three thick black stripes, this its tail fools predators by
fish swims among rocks and coral, making them believe the fish is
blending in with its environment. bigger than it really is.

HARLEQUIN TUSKFISH
Choerodon fasciatus
One of the most brightly colored
species of fish in the tropical seas,
this fish is endangered by its
popularity with aquarium aficionados.

MANDARIN DRAGONET
Synchiropus splendidus

Covered with psychedelic swirls in
green, blue, and yellow, this is one of
the most beautiful fish on the planet.
This small species lives hidden among
the rocks of coral reefs.

28 LIFE IN THE WATER

Assortment of Shapes

M ost fish have a typical streamlined shape, as exemplified by salmon or trout.
Other species have developed widely varying characteristics as adaptations to
their environment or diet. The longnose hawkfish has a pronounced proboscis for
eating invertebrates on the seabed. The stiff, slender body of the longhorn cowfish causes
it to swim slowly and clumsily. And the clown knifefish has a
flattened, knifelike body that enables it to move
more easily through the water.

FIRE GOBY
Nemateleotris magnifica
In the Indian and Pacific oceans this
fish swims among coral reefs in search
of food. Its other name, fire dartfish,
comes from its pronounced
upright dorsal fin. This
small fish is barely the
size of a finger.

PRICKLY LEATHERJACKET LONGHORN COWFISH
Chaetodermis penicilligerus Lactoria cornuta
Inhabiting coral reefs in the
tropical waters of the Indian and inhabits the Pacific Ocean
Pacific oceans, Australia, and and the Red Sea. Its rigid
northern Japan, this fish can be skeleton makes it a clumsy
up to 12 inches (30 cm) long. swimmer in spite of its
beautiful silhouette. It has
SEAWEED PIPEFISH two horns on the upper
Syngnathus schlegeli part of its head.

RED HANDFISH
Brachionichthys politus

Limited to coastal habitats
of Australia, this inoffensive
fish has an average size of 6
inches (15 cm).

FISH AND AMPHIBIANS 29

CLOWN KNIFEFISH CLOWN CORIS
Chitala chitala Coris aygula

The name knifefish comes This tropical fish of the
from its flattened shape. It Indo-Pacific region is
inhabits the waters of white in front with
southern Asia and swims black spots, which are
mainly with its anal fin. more densely scattered
near the head and
disappear completely
before the tail is
reached.

ANGELFISH
Pterophyllum scalare

Inhabiting South American
rivers in the central Amazon
system and its tributaries as
far as eastern Peru and
Ecuador, this fish has faint
stripes across its body.

LONGNOSE HAWKFISH
Oxycirrhites typus
Inhabiting coral reef zones in the
Indian and Pacific oceans, this
fish is marked by brown stripes
that form a grid. It uses its long
nose to trap prey.

SPOTTED SCORPION FISH
Scorpaena plumieri
The most poisonous of all sea
creatures, this fish eats small
fish and mollusks. Its body is
specially designed to mimic
the seafloor.

30 LIFE IN THE WATER

You Are What You Eat CORAL
Parrotfish feed
M ost fish feed in their natural environment, the larger fish eating on corals.
the smaller ones, and the smallest sea creatures feeding on
marine plants. A fish's mouth gives many clues about its feeding
habits. Large, strong teeth indicate a diet of shellfish or coral; pointed
teeth belong to a hunting fish; and a large mouth that is open while the fish
swims is that of a filterer. Some species can also trap food that lives outside
the water: trout, for example, hunt flies.

Predators MOUTH

These are fish that feed on other species. They acts as a filter.
have teeth or fangs that help them to wound As it swims
along with its
and kill their prey or to hold it fast after the mouth open,
attack. Predators use their sight to hunt, zooplankton and
although some nocturnal species such as small fish are
moray eels use their senses of smell and trapped.
touch and those of their lateral line.
All predators have highly evolved WHALE SHARK
stomachs that secrete acid to Rhincodon typus
digest meat, bones, and scales.
Such fish have a shorter intestinal Filterers
tract than herbivorous species, so
digestion takes less time. Some species have evolved to the point of being able to
take from the water only those nutrients they need for
PIRANHA feeding. They filter the nutrients out using their mouths
Pygocentrus sp. and gills. These species include whale sharks (Rhincodon
typus), herring (Clupea sp.), and Atlantic menhaden
RAZOR-SHARP (Brevoortia tyrannus).
TEETH
Plants
Large, sharp teeth
go along with a Life in the water is based on phytoplankton,
predator's diet. which is eaten by zooplankton. These are in
turn eaten by fish, all the way up
Symbiosis to the large marine species.

is the interaction between two organisms that live in close cooperation. One type
of symbiosis is parasitism, in which one organism benefits and the other is
harmed. An example of a parasite is the sea lamprey (Petromyzon marinus), which
sticks to other fish and sucks their body fluids to feed itself. Another type of
symbiosis is commensalism, in which one organism benefits and the other is not
harmed. An example is the remora (Remora remora), or suckerfish, which sticks

to other fish using suction disks on the end of its head.

SUCKERS

They close their eyes, turn
them, and push them
downward to increase the
pressure of the mouth.

REMORA
Remora remora

Grazers FUSED TEETH FISH AND AMPHIBIANS 31

This group of fish eats vegetation or Parrotfish have a strong beak that DIFFERENCES
coral in small bites. Parrotfish (Scaridae) enables them to bite the bony
have a horny beak made of fused teeth. skeleton of corals and eat the algae Carnivorous fish eat all sorts of species, even
They scrape the fine layer of algae and that grows on them. The beak is though their basic diet consists of meat. They
coral that covers rocks and then crush it actually made of individual teeth, have terminal-type mouths, muscular stomachs,
into powder using strong plates in the arranged in a beaklike structure. and short intestinal tracts. Herbivores feed on
back of the throat. aquatic vegetation. They have a long intestinal
tract compared with other fish.
PHARYNGEAL PLATES
PARROTFISH
After biting a clump of coral Scarus sp.
covered with algae, the
pharyngeal plates, strong
grinding structures in the throat,
crush the hard, stony pieces.

Types of Mouths

Terminal Superior

Inferior Protusible

Suckers STURGEON
Acipenser sp.
Species that live in the
depths, such as sturgeons THE BARBELS
(Acipenseridae) and VACUUM
suckerfish (Catostomidae), The sturgeon has a
spend their days sucking the mud Sucking fish use their prominent snout. In
on the seafloor. When they are cut mouths like a large its mouth it has four
open, large amounts of mud or vacuum cleaner to hunt sensitive barbels.
sand are found in the stomach and their prey.`
intestines. Digestive mechanisms
process all this material and
absorb only what is needed.

32 LIFE IN THE WATER

Life Cycle

I n an underwater environment, animals can simply secrete their sex cells into the water. But for
fertilization to be effective, the male and the female must synchronize their activities. Many
species, such as the salmon, travel great distances to meet with potential mates. Upon meeting
a mate they release their sex cells. The time and place are important because the survival of the
eggs depends on the water temperature. Parent-child relations are extremely varied, from complete
neglect of the eggs once laid to constant watchfulness and protection of the young.

External Fertilization 2 HATCHING90 AND 120 DAYS
The period of time needed
In most fish, fertilization is external to the female's for the eggs to hatch
body. The male secretes sperm onto the eggs as
soon as they leave the female's body. Typically, the Male salmon
young hatch from the eggs as larvae. Salmon is one
species that reproduces this way.

Female salmon

A The ovule and B The small C Then the
the sperm living being embryo forms.
join to form begins to
the egg. grow.

1 Egg Laying All salmon begin life in fresh
water and then migrate to
DAY 1 the sea. To lay eggs, they
After traveling from the sea to the return to the river.
river, the female lays her eggs in a
nest she digs in the gravel. The
strongest available male then
deposits his sperm over them.

The female
lays between
2,000 and
5,000 eggs.

FISH AND AMPHIBIANS 33

BODY OF BODY OF Parents
THE FRY THE FRY
The yellow-headed jawfish,
3 YOUNG FRY'S Opisthognathus aurifrons,
FISH (FRY) YOLK SAC incubates its eggs inside
121 DAYS its mouth.
The small fry feed
from the yolk sac. Mouth Incubation

6 Year The gestation of some fish species takes place
Cycle inside the parents' mouths. They incubate the
eggs inside their mouths and then spit them out
This is the life into the burrow. Once the eggs hatch, the
span of a salmon. parents protect their young by sheltering them
again inside their mouths.

Internal Fertilization

Viviparous fish give birth to their young in the
form of developed juveniles. Fertilization is
internal, carried out by a male organ called the
gonopod, which is a modified fin.

Ovary Paraplacental
uterine space

Umbilical cord
Placenta

4 Juveniles

5 Adults 2 years Young male
Salmon fry grow until they
6 years become small juvenile salmon.
The adult salmon have fully They migrate to the sea, where
mature reproductive organs, and they live for four years.
they return to the river where
they were born to lay their eggs. Young female

Ovary Urogenital
opening

34 LIFE IN THE WATER

Matters of Life and Death

T o survive, most fish need adaptations to enable them to flee from their
predators or to find food. The European plaice can lie on the ocean floor
with its flat body. Its ivory color makes it almost invisible. The
flying fish, on the other hand, developed pectoral fins to lift itself
up over the surface of the water and flee its enemies.

European Plaice VENTRAL SIDE
remains an ivory
The European plaice (Pleuronectes platessa) is a flat color, devoid of
fish with a shape especially designed to allow it to pigmentation. This
remain motionless on the seafloor. It also provides an side rests on the
example of mimesis. Its two sides are very different. ocean floor.
The top side is pigmented with small red spots
that camouflage the fish on the seafloor,
where it uses its fins to cover itself with
sand to hide from predators.

MOUTH EUROPEAN
PLAICE
The European plaice's entire body Pleuronectes
undergoes metamorphosis from its larval platessa
state to adulthood. The mouth, however,

remains the same.

EYES
Both are
located on the
right side.

Transformation GILLS
The European
At birth, the European plaice does not have a flat plaice breathes
form but looks like a normal fish. It eats near the through its gills.
surface and swims using its swim bladder. As time
goes by, its body becomes flat. The swim bladder
dries up, and the fish sinks to the bottom of the sea.

1 5 days OPERCULUM
0.14 inch (3.5 mm) is the bone that
supports the gill
structure.

The vertebrae
begin to form.

One eye on each side 2 10 days 3 22 days
0.15 inch (4 mm) 0.31 inch (8 mm)
45 days
The fold of the fin The cleft of
is the amount of time the European plaice takes to is forming, and the tail
become a flat fish from a typical streamlined larva. the mouth is develops.
already open.

The left eye
moves to the top
of the head.

FISH AND AMPHIBIANS 35

Flying Fish 1 2 They reach

Exocoetidae, or flying fish, are a family of ESCAPE TAKEOFF heights of up to
ocean fish that includes 52 species grouped When a predator The fish comes to the 19 feet (6 m).
in eight genera. They are found in all the appears, the flying fish surface and elevates
oceans, especially in warm tropical propels itself out of itself as high as it can, 3 GLIDING
and subtropical waters. Their most the water. skipping over the water. The average gliding distance is
surprising characteristic is their
unusually large pectoral fins, 160 feet (50 m), but they can
which give them the ability
to fly and glide for glide as far as 660 feet (200 m).
short distances.

Flying fish measure from These fish cover distances of up to 160 feet (50 m) in the air.
7 to 18 inches
ANATOMY
(18 to 45 cm) long. This fish slides over the
water with its hardened
fins, and it can reach
speeds up to 40 miles
per hour (65 km/h) for
as long as 30 seconds.

This fish has
highly developed
pectoral and
pelvic fins.

SPOTS FLYING FISH
are useful for Exocoetus volitans
camouflage in the
sand and for hiding Scorpion Fish
from its predators.
Found in the reefs of the Gulf of Mexico, Scorpaena
plumieri, known commonly as the scorpion fish, has a
brown, spotted body with many appendages that look
like moss between its mouth and its eyes. This fish is
hard to see because its texture and color help it blend
easily into the seafloor. Its dorsal fins have a powerful
venom, which causes intense pain.

FIN CAUDAL FIN SCORPION FISH
The dorsal, anal, and Thin, barely used Scorpaena plumieri
caudal fins form a for swimming.
continuous line
around the body.

4 45 days The pigment cells join
0.43 inch (11 mm) to form dark spots.

It no longer
looks to the
right, but
upward.

36 LIFE IN THE WATER

The Best Disguise

T o face their enemies, fish have developed a number of
strategies to enable them to survive. Some of these
are escaping, hiding in the ocean bed, or stirring up
sand to avoid being seen. Other species have poison, and
some can inflate and raise barbs or spines to discourage
predators. In the oceans' depths are fish that have
luminous organs that blind the enemy.

Spot-Fin Porcupine Fish

Like its relative the globefish, this fish predator. This fish has another
swallows water when it feels defense mechanism: its modified
threatened, swelling up to three times scales act as barbs. When the fish's
its normal size. This makes it very size increases, the scales extend
difficult to fit inside the mouth of a perpendicularly from the skin.

Spinal column

Water Stomach The spine
curves.
HOW IT INFLATES
The water enters through the fish's The stomach
mouth. The stomach stores water fills with
and begins to increase in size. The water.
spinal column and the skeleton are
flexible and adapt. If the fish is
taken out of the water, it can
inflate in a similar way by
swallowing air.

At Rest Self-Defense

The scales of the porcupine fish lie flat against Inflated porcupine fish can reach a diameter of up to 35
its body, and its appearance is no different from inches (90 cm). This makes swallowing them impossible
that of any other bony fish. When it deflates for medium-size predators, which are frightened simply
after an attack, it returns to its original state. by the porcupine fish's appearance.

FISH AND AMPHIBIANS 37

Sharp Enough to Cut

The sharp blades of the yellow tang's caudal
appendage look like scalpels. This fish can
retract and extend its blades at will to hurt
potential attackers. The fish eats only algae;
it measures some 20 inches (50 cm) long.

YELLOW TANG This fish frequently
Zebrasoma swims in schools
flavescens with fish of other
species.

Strange Garden

Garden eels can bury much of their body
in the sandy seafloor and become stiff. A
group of buried garden eels looks like a
colony of algae or coral, even though their tiny
eyes are on the lookout for the small species
they eat. At the slightest sign of danger, they
go into their burrows.

Eels in a The eel hardens its
group muscled body and
buries its tail, leaving
its head in the open.

Walls covered with
mucus secreted by
the skin of the
animal's tail

GARDEN EEL
Taenioconger hassi

SPOT-FIN STIFF SPINES
PORCUPINE FISH Modified scales, hard and resistant,
Diodon hystrix are found all over its body, except for
the tail. When these scales are
extended, it is almost impossible for a
predator to bite or swallow this fish.

Diversity

T he ocean depths are inhabited world. The most feared fish is the great
by many types of fish. Some are white shark, a true underwater predatory
harmless, but others, such as machine—though it seldom attacks
the scorpion fish, are among the humans. In this chapter we will also tell
most poisonous creatures in the you about the odyssey of many salmon

SHARK LONG AND FLEXIBLE 40-41 HABITAT, TASTES, AND PREFERENCES 50-51
To locate its prey, the shark ELEGANT CONTOURS 42-43 DANGER IN THE WATER 52-53
uses several of its senses-smell DEADLY WEAPON 44-45 KINGS OF DARKNESS 54-55
and hearing over long distances TIME TO EAT 46-47 SEA SNAKES 56-57
and sight at short range. THE JOURNEY HOME 48-49 OUT OF THE WATER 58-59

and trout species, which can travel and it involves many dangers. It requires
thousands of miles from their ocean so much energy that, after laying their
home to lay their eggs in the rivers or eggs, many females die.
lakes where they were hatched. The
journey lasts from two to three months,

40 DIVERSITY

Long and Flexible

T he seahorse is a small ocean fish that belongs to the same family as pipefish and sea
dragons (Syngnathidae). Its name comes from its horselike head. In fact, no other fish
genus has its head at a right angle to the rest of its body. Because it cannot use speed
to escape from its predators, the seahorse has the ability to change color to blend in with its
environment. The reproduction process of these fish is also very unique. The male has an
incubating pouch in which the female deposits the fertilized eggs.

BLACK-STRIPED PIPEFISH Movement EYES
Syngnathus abaster Large, for
The body of a seahorse is crammed into an acute vision
One of the slowest fish in the sea, the armor of large, rectangular bony plates.
black-striped pipefish moves by means They swim very differently than other fish. NOSE
of slight undulations of its pectoral Adopting an upright position, they use their Pipe-shaped,
fins, which can vibrate up to 35 dorsal fin for propulsion. They do not have giving the
times per second. an anal fin, but rather a long tail that rolls head a
into a spiral. They use it to hold onto horselike
Classification underwater plants. shape

Thirty-two species of seahorse have been identified HEAD
worldwide. Classifying them is at times complicated
because individuals of the same species can change color ROLLED UP UNROLLED TRUNK
and develop long filaments of skin. The size of adult The tail rolls up The tail The body is
seahorses varies enormously, from the tiny Hippocampus into a curl. straightens out supported
minotaur—a species discovered in Australia that never by unrolling. by the spinal
grows beyond 0.7 inch (1.8 cm) long—to the enormous column.
Hippocampus ingens, a species in the Pacific that reaches GRASPING TAIL
over 12 inches (30 cm) long. It has no pelvic or caudal fins, With their long TAIL
but it does have a tiny anal fin. tails, seahorses can Can be
cling to plants on extended to a
WEEDY SEA DRAGON the seafloor. fully vertical
Phyllopteryx taeniolatus position

Its shape is typical of this family,
although its tail is not suitable for
grasping, like those of seahorses are,
and it has a more elongated profile.
Its body is covered with seaweed.

SEAWEED Camouflage LINED SEAHORSE
The fish lets it stick Hippocampus
to its body so that Since they cannot use speed to escape erectus
it can escape from predators, seahorses and dragon
detection. fish use camouflage as a defense
strategy. They change color to blend in
with their environment, grow skin Habitat Caribbean, Indo-Pacific Ocean
filaments shaped like seaweed, and use Number of species 35
their heads to climb along the seaweed Size 7-12 inches (18-30 cm)
in which they live, swinging from one
plant to another.

FISH AND AMPHIBIANS 41

GILLS 35 Reproduction
Seahorses breathe species
through gills. The male has an incubating pouch in which the
of seahorses live in the female deposits her eggs. The sac closes, and
Caribbean, the Pacific Ocean, the embryos develop, nourished by the male. He
and the Indian Ocean. later expels the young, now mature and
independent, through a series of contractions.

PECTORAL FIN
One on each side,
for lateral
movement

0.4 During the mating season the female lays
inch
1 some 200 eggs in the male's pouch using her
(1 cm) egg-depositing organ. There the eggs are
fertilized. When the time for birth arrives,
The size of a the male clings to seaweed with his tail.
seahorse at birth

BONY PLATES The male bends his body backward and
Its body is covered
with concentric rings 2 forward, as if having contractions. The sac's
of bone. opening widens, and the birthing process
begins. Soon the young begin to appear.
DORSAL FIN
Seahorses swim
upright, propelled by
their dorsal fin.

As the male's belly contracts, the young

3 seahorses are gradually born. Each one is
0.4 inch (1 cm) long. They begin to feed
on phytoplankton right away. The
birthing process can last two days, after
which the male is exhausted.

42 DIVERSITY

Elegant Contours Tail Pectoral fin
Head
T he Rajiformes are an order of cartilaginous fish related to sharks; RAYS
they have the same skeletal structure, the same number and type Raja sp.
of fins, and similarly shaped gill slits. Rajiformes are distinct in that
their gill slits are on the underside of the body, which is flat with pectoral
fins joined to the trunk in the shape of a disk. The body is usually
covered with denticles, and many have a row of dorsal spikes. They
have a variety of colors, with spots and blotches. They often burrow
into the mud of warm seas.

Flying Through POISONOUS TAIL BLUE LINES
has a dangerous run along the whole
the Water stinger. length of the tail.

Unlike most fish, rays have weak, slender tails
that do little to power their swimming. They
move with their enormous pectoral fins, which are
joined to the head and have a characteristic rhomboid
shape. Their movement rises and falls in an S curve,
as if they were flying underwater.

ROUGH RAY PECTORAL
Raja radula FINS
are joined to the
TAIL body just behind the
is slender and lacks head near the gills.
the strength for
swimming. Blue-spotted
Ribbontail Ray
12.4 miles
per hour Its body is covered with blue spots. It
inhabits reefs, caves, and crevices. Its
(20 km/h)
tail has a powerful stinger that
Smiling Face injects venom into predators
when it feels threatened.
The ray's face is unique. It is
protected by a flap on the Nasal orifices FINS HEAD
underside of its body. Its hornlike Hornlike mouth move up and down remains upright,
mouth is adapted for grasping during swimming. looking forward.
crustaceans, and the five gill Gill arch
slits on each side are for
breathing underwater.

LITTLE SKATE
Raja erinacea

FISH AND AMPHIBIANS 43

BLUE-SPOTTED THERE ARE Electric
RIBBONTAIL RAY ABOUT organ
Taeniura lymma Spiracle
300
Habitat Indian and Pacific oceans SPECIES OF Gill arch
Diet Crustaceans RAJIFORMES
Length Up to 6.6 feet (2 m) Muscle
Poisonous Yes
Electric
Ray

Electric rays (Torpedo sp.) are highly
active fish with electric organs on each
side of the head. Each electric organ is
made of numerous disk-shaped cells,
connected in parallel. When all the cells fire
at once, an electric current is discharged into
the water at 220 volts, enough to stun the prey.

PELVIC FINS
Small in size

EYES TAIL WITH
Turned outward ELECTRIC CHARGE

PECTORAL FINS
Joined to the head

Nasal Mouth
orifices
Row of teeth

COMPARED MANTA 23 feet (7 m) 8.2 feet (2.5 m) 3.3 feet (1 m) Sawfish
FOR SIZE RAY
Weight 3,300 BUTTERFLY THORNBACK Fish of the order Pristiformes have long bodies with an
The manta ray is the pounds (1,500 kg) RAY RAY unmistakable face, adorned with 32 pairs of denticles on
largest in the world. In each side. The females give birth to 15 to 20 young,
spite of its large size, it is which are born with a protective membrane over their
harmless, feeding only on teeth to keep from hurting the mother.
sea plankton.

44 DIVERSITY

Deadly Weapon

O ne of the greatest predators in the ocean is the great white shark, NASAL
easily identified by its distinctive white coloring, black eyes, and fierce PITS
teeth and jaws. Many biologists believe that attacks on humans result
from the shark's exploratory behavior, because these fish often lift their EYES
heads above the water and explore things by biting them. This activity is They have
often dangerous because of the sharpness of the sharks' teeth and the poor vision
strength of their jaws. Great white sharks are implicated in most fatal shark and use their
attacks on humans, especially on surfers and divers. sense of
smell to hunt.
Senses SHARK ATTACKS 23
1876-2004 JAW
Sharks have senses that most MEDITERRANEAN During an
animals lack. The ampullae of attack, it
Lorenzini are small clefts in the shark's stretches
head that detect electricity. This sense forward.
helps them find prey hidden in the sand.
The lateral line is used to detect movement 84 8 1 2
or sound underwater. Smell is their most
advanced sense, and it occupies two thirds WEST EAST SOUTH JAPAN
of their brain. They also have a highly COAST COAST KOREA
developed sense of hearing, which allows OF U.S. OF U.S.
them to detect very low-frequency sounds.
1

MEXICO

3 10

SOUTH NEW
AMERICA ZEALAND

Hearing Ampulla of 47 41
Detects sounds Lorenzini
of very low Detects nerve SOUTH AFRICA AUSTRALIA
frequency impulses

220 DORSAL
FIN
ATTACKS IN
128 YEARS

Lateral line Nose
detects The most highly
movements or developed sense
sounds is smell; it takes
underwater. up two thirds of
the brain.

Electric CAUDAL FIN ANAL
radar The great white FIN
shark has a large
GREAT WHITE heterocercal PELVIC FIN
SHARK caudal fin.
Carcharodon
carcharias

Habitat Oceans PECTORAL FIN
Weight 4,400 pounds (2,000 kg) Highly developed
Length 23 feet (7 m) and very important
Life span 30-40 years for swimming

FISH AND AMPHIBIANS 45

SNOUT BODY PARTS MOST 33% 24% 20%
Detects the FREQUENTLY
odor of ATTACKED Hips Head Hands
nearby prey
23% 40% 23%

Feet Abdomen Arms

40%

Legs and
knees

Snout

1 RAISED
SNOUT

The head is raised

and the jaws open.

TEETH 2 THE JAWS
ADVANCE
Serrated If a tooth is lost in
edge front, it is replaced The shark grabs the prey
by another tooth
Serrated that moves forward with its teeth and holds
edge from a row that
grows behind. it until it is dead. Teeth
Throat
Serrated REPLACEMENT
edge TEETH

Sharks lose thousands of
teeth throughout their lives,
but each one is replaced with
a new tooth.

JAW

New teeth

COMPARISON The great white shark, at 23 feet Jaw
WITH OTHER (7 m) long, is one of the largest
SPECIES of its genus. The shark's jaws are made of cartilage instead of
bone, and they are located underneath the skull.
When the animal closes in on its prey, it raises its snout.
The jaws slide forward, away from the skull, for a better
grip. Most shark teeth have serrated edges for cutting
flesh. The sharp points are for perforating, and the wide,
flat surfaces are for crushing.

9.8 feet (3 m) 11.2 feet (3.4 m) 23 feet (7 m)
BULL SHARK LEMON SHARK GREAT WHITE SHARK

46 DIVERSITY

Time to Eat In a vertical
position, it
M ost fish feed within their aquatic environment. Some species, sees the prey
however, seek their food outside the water. The best-known well enough
example is the archerfish, which shoots streams of water from to attack it.
its mouth to knock spiders and flies off nearby plants and into the water.
The African butterfly fish eats flying insects, which it traps after a brief
flight. The river hatchetfish has a similar strategy: its long pectoral
fins and flattened body enable it to make great leaps.

Archerfish Technique Angle of vision At an angle close to 5 feet
90° to the surface
Seven species of archerfish live in the The tongue presses upward against Archerfish have large of the water, it (1.5 m)
tropical waters of India and southeast Asia. a groove in the roof of the mouth, eyes and excellent vision focuses on the prey.
They hunt using an unusual technique of forming a tube for emitting the for hunting. Range of the
spitting streams of water. stream of water. water stream for
90º an adult fish
Groove in roof Movement
of mouth of tongue EXACT ANGLE OF 4 inches
VISION
3.1 (10 cm)
inches The tongue acts
(8 as a valve to Range of the
cm) keep the water water stream for
under pressure. a young fish

9.4 inches (24 cm)

Strategy It looks at
the prey and
The carnivorous archerfish has developed a shoots a
special strategy for hunting live insects, which is stream of
highly effective for hunting prey outside the water.
water at distances of up to 5 feet (1.5 m).

When the
insect falls
into the water,
the fish
devours it.

A SEARCH B SHOT C AIM
The archerfish When it finds its prey, If the first
looks upward in the archerfish positions stream misses,
search of its prey. its body upright and the fish tries
shoots a stream of again and again.
water at the target.


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