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Introduction to Vertebrates
Chapter 39
Fishes
Introduction to Vertebrates
• Vertebrates are members of the subphylum
Vertebrata, within the phylum Chordata.
All Chordates share the following
characteristics.
•
•
•
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Notochord
Dorsal hollow nerve cord
Pharyngeal pouches
Post-anal tail
Introduction to Vertebrates
Vertebrates are distinguished from chordates
by:
• Vertebrae - bones or cartilage that surround
the dorsal nerve cord and form the spine.
• A cranium - a skull that protects the brain
• An endoskeleton - an internal skeleton made
of bone or cartilage
Introduction to Vertebrates
• Myxini - hagfishes
• Cephalaspidomorphi - lampreys
• Chondrichthyes - sharks, rays, skates, and
ratfishes
• Actinopterygii - ray-finned fishes
• Sarcopterygii - lobe-finned fishes
• Amphibia - frogs, toads, salamanders, and
caecilians
• Reptilia - lizards, snakes, and turtles
• Aves - birds
• Mammalia - mammals
Introduction to Vertebrates
Vertebrate Evolution
• Most biologists think that vertebrates
originated about 560 million years ago.
• The first fish were jawless.
Vertebrate Evolution
• About 450 million years ago, the first
fishes with jaws and paired fins
appeared.
• Jaws are thought to have evolved from
the first pair of gill arches, the skeletal
elements that support the pharynx.
Vertebrate Evolution
The advantages to jaws and paired fins:
• Paired fins increased fishes’ stability
and maneuverability in water
• Jaws allowed fishes to seize and
manipulate prey
Jawless and Cartilaginous Fishes:
Fish Adaptations
Fish have several adaptations that make them
well suited to life in water:
• Streamlined body plan - allows fish to move
rapidly in water
• Adaptations for buoyancy - stored gases or lipids
help maintain vertical position in water
• Efficient respiration - internal gills exchange
gases efficiently
Jawless and Cartilaginous Fishes:
Fish Adaptations
Adaptations for salt and water homeostasis -
• The concentration of solutes in a fish’s
body usually differs from the concentration
of solutes in the water.
• Fish have adaptations to maintain ion and
water homeostasis.
Jawless and Cartilaginous Fishes:
Fish Adaptations
Sensory adaptations - Fish have a
variety of organs that allow them to
sense their environment.
• Sight: fish eyes are similar to eyes of
land vertebrates
• Sound: fish have internal ears
sensitive to sound
Jawless and Cartilaginous Fishes:
Fish Adaptations
Chemoreception: the ability to detect
chemicals in the environment
includes the senses of smell and
taste.
Jawless and Cartilaginous Fishes:
Fish Adaptations
• Fish have nostrils and tastebuds.
Tastebuds may be located in their
mouths, on their lips, fins, and skin,
and on whisker-like organs called
barbels.
Jawless and Cartilaginous Fishes:
Fish Adaptations
Unique senses:
• Lateral line: the lateral line is a system of canals in
the skin that allow fish to sense vibration in the
water
• Ampulae of Lorenzini: cartilaginous fishes have
sense organs called ampulae of Lorenzini that can
detect weak electrical fields
• Electroreception and Magnetoreception: some
fish have the ability to detect electrical and magnetic
fields
Lateral
Line
in Fishes
Jawless Fishes
Only two classes of jawless fishes are alive
today:
• Hagfishes (class Myxini) Hagfishes are
bottom-dwellers that feed on dead and
dying fish.
Jawless Fishes
• Lampreys (class Cephalaspidomorphi)
Lampreys can be free-living or parasitic.
Parasitic lampreys attach themselves to
their host with disc-shaped mouths and
feed on the blood and body fluids of other
fishes. All lampreys breed in fresh water.
Fertilization occurs outside the body external fertilization.
Cartilaginous Fishes
All cartilaginous fishes:
• belong to the class Chondrichthyes.
• have skeletons made of cartilage - a
flexible lightweight material made of cells
surrounded by tough fibers of protein.
Cartilaginous Fishes
All cartilaginous fishes:
• have skin covered with placoid scales small, toothlike spines that feel like
sandpaper.
• Placoid scales probably reduce turbulence
and increase swimming efficiency.
Cartilaginous Fishes
Sharks:
• Sharks have torpedo shaped bodies that
reduce turbulence when swimming,
called a fusiform body shape.
• Some sharks are filter feeders, and have
slender projections on the inner surface
of their gills, called gill rakers, that filter
the water.
Cartilaginous Fishes
Sharks:
• The mouth of a typical shark has 6 to
20 rows of teeth. When a tooth breaks
or wears down, a replacement moves
forward. One shark may use more
than 20,000 teeth over its lifetime.
Cartilaginous Fishes
Rays and Skates:
• Rays and skates have flattened bodies
with paired wing-like pectoral fins and, in
some species, whip-like tails.
• Rays have diamond- or disk-shaped
bodies. Most skates have triangular
bodies.
Cartilaginous Fishes
Rays and Skates:
• Rays and skates are primarily bottom
dwellers, and most feed on mollusks and
crustaceans.
Cartilaginous Fishes
Ratfishes:
• Ratfishes are a small group of strange
looking fish that have a flap of skin
covering their gill slits.
• Ratfishes have long, rat-like tails and feed
on crustaceans and mollusks.
Adaptations in Cartilaginous Fishes:
• Some sharks push water through
their mouth and over their gills by
swimming.
• Most cartilaginous fish pump water
over their gills by expanding and
contracting their mouth cavity and
pharynx.
Adaptations in Cartilaginous Fishes:
• When lying on the bottom, rays and
skates draw water in to their gills
through spiracles, two large openings
on the top of the head, behind the
eyes.
• Sharks convert ammonia to urea in
their bodies.
• Sharks retain large amounts of urea
in their bodies to raise the
concentration of solutes in their
bodies to the same level as that found
in sea water.
• Sharks still tend to take up sodium
and chloride ions.
• The rectal gland removes excess
sodium and chloride ions from the
body.
Cartilaginous fishes maintain their position in
the water in two ways.
1.The caudal and pectoral fins generate lift,
or upward force, as the fish swims.
2.Many cartilaginous fish store large
amounts of lipids, usually in the liver.
Lipids are less dense than water.
Reproduction in Cartilaginous Fishes:
• Fertilization occurs inside the body of the
female, called internal fertilization.
• Some cartilaginous fish lay eggs.
Reproduction in Cartilaginous Fishes:
• The eggs of many species develop within
the female’s body.
• In some species, the mother nourishes the
developing young while they are in her
body.
Bony Fishes:
Characteristics of Bony Fishes
Bony fishes have three key features:
• Bone - the skeletons of most bony fishes contain
bone.
• Lungs or swim bladder - early bony fishes had
lungs, organs which exchange gas between the air
and blood. Most bony fishes today have a swim
bladder, a gas-filed sac that is used to control
buoyancy.
• Scales - scales protect the body of a bony fish and
reduce friction when swimming.
Swim
Bladder in Bony
Fish
Bony Fishes:
Characteristics of Bony Fishes
There are two main groups of bony fishes:
• Lobe-finned fishes - have fleshy fins
supported by a series of bone.
• Ray-finned fishes - have fins that are
supported by long, segmented, flexible
bony elements called rays.
Bony Fishes:
External Anatomy
• Operculum: Most bony fish have an
operculum, a hard plate that opens at the
rear and covers and protects the gills.
• Fins: The fins of most fish are supported
by rays or spines. Rays are flexible,
spines are rigid.
Bony Fishes:
External Anatomy
• Skin: The skin of most bony fish are
covered with scales. Scales are thin,
round disks of a bonelike material that
grow from pockets in the skin and overlap
like shingles.
Yellow Perch
Bony Fishes:
Internal Anatomy
Digestive system ---• Food passes from the mouth into the
pharynx, through the esophagus, to the
stomach.
• From the stomach food passes into the
intestine, where nutrients are absorbed.
• Undigested material is eliminated through
the anus.
Bony Fishes:
Internal Anatomy
Circulatory system:
• The circulatory system of a fish
delivers oxygen and nutrients to the
cells of the body.
• The circulatory system consists of a
heart, blood vessels, and blood.
Internal Structure
Bony Fishes:
Internal Anatomy
Circulatory system:
• The heart pumps blood through
arteries to small, thin-walled vessels
called capillaries, in the gills.
• From the gills, the blood travels to the
body tissues, where nutrients and
wastes are exchanged.
• The blood returns to the heart through
veins.
Bony Fishes:
Internal Anatomy
Circulatory system
The heart of a bony fish has two chambers in a row, as
shown below. Blood from the body enters the sinus
venosus, moves into the atrium, then into the ventricle.
From the ventricle it enters the conus arteriosus, and
then goes to the gills.
Bony Fishes:
Internal Anatomy
Respiratory system
• Fish use gills for gas exchange.
• Water flows across the gill filaments in a
direction opposite to blood flow, called
countercurrent flow.
Bony Fishes:
Internal Anatomy
• Countercurrent flow allows more oxygen to
diffuse into the blood than would be
possible if blood and water flowed in the
same direction.
Bony Fishes:
Internal Anatomy
Excretory system
• The kidneys filter chemical wastes from
the blood to form urine, a solution
containing ammonia, ions such as salts,
and water.
• The kidneys help regulate the ion and
water balance in fish.
Bony Fishes:
Internal Anatomy
• The gills also allow wastes to diffuse
from the blood into the water and help
regulate ion and water balance in fish.
Bony Fishes:
Internal Anatomy
Swim bladder
• The swim bladder is a thin-walled sac in the
abdominal cavity that contains a mixture of
oxygen, carbon dioxide, and nitrogen obtained
from the bloodstream.
• Swim bladders evolved from balloonlike lungs,
which ancestral bony fishes may have used to
supplement the oxygen absorbed by the gills.
Bony Fishes:
Internal Anatomy
Swim bladder:
• In some fish the swim bladder is known
to amplify sound by vibrating and
transmitting sound to the inner ear.
Bony Fishes:
Internal Anatomy
Nervous system
The nervous system of a bony fish includes
the brain, spinal cord, nerves, and
various sensory organs.
Internal Structure
Bony Fishes:
Internal Anatomy
The fish brain consists of several parts:
• Olfactory bulb - processes information about smell
• Cerebrum - integrates information from other parts of
the brain
• Optic tectum - processes information about sight and
from the lateral line system
• Cerebellum - coordinates muscle movement and
balance
• Medulla oblongata - controls the function of some
organs and relays information from the spinal cord
Bony Fishes:
Internal Anatomy
Spawning
• Reproductive behavior in bony fishes is called
spawning.
• Fertilization in most fish takes place outside the body.
• Many species of fishes lay large numbers of eggs.
• Some species of fish carry the eggs within their bodies
until the eggs hatch.