30-2 Fishes
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What Is a Fish?
What Is a Fish?
Fishes are aquatic vertebrates. Most fishes have
paired fins, scales, and gills.
Fishes are so varied that for almost every general
statement there are exceptions (ie: catfish don’t have
scales)
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Evolution of Fishes
Evolution of Fishes
Fishes and nonvertebrate chordates probably
evolved from common invertebrate ancestors.
The evolution of jaws and the evolution of paired fins
were important developments during the rise of
fishes.
The First Fishes
The earliest fishes to appear in the fossil record lived
about 510 million years ago.
These fishes were jawless and had bodies covered
with bony plates.
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Evolution of Fishes
The Age of Fishes
During the Ordovician and Silurian Periods, 505410 million years ago, fishes underwent a major
adaptive radiation. These species then ruled the
seas during the Devonian Period, often called the
“Age of Fishes”.
Some fishes were jawless species that had very
little armor. These are the ancestors of modern
hagfishes and lampreys.
Armored fishes became extinct at the end of the
Devonian Period.
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Evolution of Fishes
The Arrival of Jaws and Paired Fins
The evolution of jaws in fish was extremely useful.
Jaws with muscles and teeth made it possible for fish
to eat a wider variety of foods.
Animals with jaws can also defend themselves by
biting.
Fishes evolved paired pectoral (anterior) and pelvic
(posterior) fins.
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Evolution of Fishes
These fins were attached to girdles—structures of
cartilage or bone that support the fins.
Cartilage is a strong tissue that supports the body
and is softer and more flexible than bone.
Paired fins gave fishes more control of body
movement.
Tail fins and powerful muscles gave fishes greater
thrust when swimming.
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Evolution of Fishes
The Rise of Modern Fishes
Early jawed fishes soon disappeared, but left behind
two major groups that continued to evolve and still
survive today.
One group—the ancestors of modern sharks and
rays—evolved a skeleton made of strong, resilient
cartilage.
The other group evolved skeletons made of true
bone.
A subgroup of bony fishes, called lobe-finned fishes,
had fleshy fins from which the limbs of chordates
would later evolve.
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Form and Function in Fishes
Form and Function in Fishes
Adaptations to aquatic life include various modes
of feeding, specialized structures for gas
exchange, and paired fins for locomotion.
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Form and Function in Fishes
Feeding
Every mode of feeding is seen in fishes.
A single fish may exhibit several modes of feeding,
depending on the type of food available, or be
extremely specialized in their food preference.
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Form and Function in Fishes
Food passes through the mouth and esophagus, into
the stomach.
In the stomach, the food is partially broken down.
Esophagus
Stomach
Mouth
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Form and Function in Fishes
In many fishes, the food is further processed in
fingerlike pouches called pyloric caeca.
The pyloric caeca secretes digestive enzymes and
absorbs nutrients from the digested food.
Pyloric cecum
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Form and Function in Fishes
The liver and pancreas add enzymes and other
digestive chemicals to the food as it moves through
the digestive tract.
Liver
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Pancreas
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Form and Function in Fishes
The intestine completes the process of digestion and
nutrient absorption.
Intestine
Only show “Intestine” label on this slide.
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Form and Function in Fishes
Undigested material is eliminated through the anus.
Anus
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Form and Function in Fishes
Respiration
Most fishes exchange gases using gills located on
either side of the pharynx.
The gills are made up of feathery, threadlike
structures called filaments.
Each filament contains a network of fine capillaries
that provide a large surface area for exchange of
gases.
Gills
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Form and Function in Fishes
Fishes use their gills to exchange gases by pulling
oxygen-rich water in through their mouths, pumping it
over their gill filaments, and pushing oxygen-poor
water out through openings in the sides of the pharynx.
Gills
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Form and Function in Fishes
Some fishes, such as lampreys and sharks, have
several gill openings.
Most fishes have a single gill opening on each side
of the body through which water is pumped out.
This opening is hidden beneath a protective bony
cover called the operculum.
Some fish have specialized organs that serve as
lungs to adapt to oxygen-poor water.
A tube brings oxygenated-air to the organ through
the fish’s mouth.
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Form and Function in Fishes
Circulation
Fishes have closed circulatory systems with a heart
that pumps blood around the body in a single loop
from the heart to the gills, from the gills to the rest of
the body, and then back to the heart.
In most fishes, the heart has four parts:
• sinus venosus
• atrium
• ventricle
• bulbus arteriosus
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Form and Function in Fishes
Oxygen-poor blood from the
veins collects in the thin
walled sinus venosus
before it flows to the atrium.
Sinus Venosus
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Form and Function in Fishes
The atrium is a large
muscular chamber that
serves as a one-way
compartment for blood
that is about to enter the
ventricle.
Atrium
Blood enters the atrium
and flows to the ventricle.
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Form and Function in Fishes
The ventricle is a thickwalled, muscular
chamber that is the
actual pumping portion
of the heart.
The ventricle pumps
blood into the bulbus
arteriosus.
Ventricle
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Form and Function in Fishes
The bulbus arteriosus is
a large muscular tube
that moves blood into the
ventral aorta and toward
the gills.
Bulbus arteriosus
It connects at its front end
to a large blood vessel
called the aorta, through
which blood moves to the
fish’s gills.
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Form and Function in Fishes
Circulation in a Fish
Gills
Body
muscle
circulation
Digestive system
circulation
Brain and
head
circulation
Heart
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Form and Function in Fishes
Excretion
Fishes eliminate nitrogenous wastes as ammonia.
Some wastes diffuse through the gills into the
surrounding water.
Others wastes are removed by kidneys, which are
excretory organs that filter wastes from the blood.
Kidneys help fishes control the amount of water in
their bodies.
Some fishes can move from fresh to salt water by
adjusting their kidney function.
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Form and Function in Fishes
Salt water fishes tend to lose water by osmosis.
The kidneys of marine fishes concentrate wastes and
return water to the body.
Kidney
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Form and Function in Fishes
Freshwater fishes tend to have a great deal of water
entering their bodies by osmosis.
The kidneys of freshwater fishes pump out dilute urine.
Kidney
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Form and Function in Fishes
Response
Fishes have well-developed nervous systems
organized around a brain, which has several parts.
Brain
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Form and Function in Fishes
The most anterior parts of the
brain are olfactory bulbs.
Olfactory
bulb
They are involved with the
sense of smell, or olfaction.
Olfactory bulbs are connected
to the lobes of the cerebrum.
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Form and Function in Fishes
In most vertebrates, the
cerebrum is responsible for all
the voluntary activities of the
body.
Cerebrum
In fishes, however, the
cerebrum primarily processes
the sense of smell.
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Form and Function in Fishes
The optic lobes process
information from the eyes.
The cerebellum coordinates
body movements.
Optic lobe
The medulla oblongata
controls the functioning of
many internal organs.
Cerebellum
Medulla
oblongata
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Form and Function in Fishes
Almost all fishes that are active in daylight have welldeveloped eyes and color vision that is at least as
good as humans’.
Many fishes have extraordinary senses of taste and
smell due to specialized cells called chemoreceptors.
Most fishes have ears but may not hear sounds well.
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Form and Function in Fishes
Fishes use the lateral line system to sense the
motion of other fishes or prey swimming nearby by
detecting gentle currents and vibrations in the water.
Some fishes can detect low levels of electric current,
like catfish and sharks.
Some fish can even generate their own electricity,
like the electric eel.
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Form and Function in Fishes
Movement
Most fishes move by contracting paired sets of
muscles on either side of the backbone.
Series of S-shaped curves move down the fish’s body.
Force and action of the fins propels the fish forward.
The fins of fishes are used to keep on course and
adjust direction. Fins also increase the surface area of
the tail, providing an extra boost of speed.
Fishes’ streamlined body shapes reduce the amount
of drag (friction) as they move through water.
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Form and Function in Fishes
Fishes’ body tissues are more dense than the water
they swim in, so sinking is an issue.
Many bony fishes have an internal, gas-filled organ
called a swim bladder that adjusts their buoyancy.
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Form and Function in Fishes
Reproduction
The eggs of fishes are fertilized either externally or
internally, depending on the species.
Fishes whose embryos in the eggs develop and hatch
outside the mother's body are oviparous, like salmon.
The embryos of oviparous fishes obtain food from the
yolk in the egg.
In ovoviviparous species, such as guppies, the eggs
stay in the mother's body after internal fertilization.
Each embryo develops inside its egg, using the yolk
for nourishment. The young are “born alive” like most
mammals.
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Form and Function in Fishes
In viviparous animals, like several shark species, the
embryos stay in the mother's body after internal
fertilization.
These embryos obtain the substances they need
from the mother's body (not from material in an egg).
The young of viviparous species are “born alive.”
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Groups of Fishes
Groups of Fishes
Over 24,000 living species
Grouped according to body structures
All living fishes can be classified into three groups:
jawless fishes, cartilaginous fishes, and bony fishes.
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Groups of Fishes
Jawless Fishes
Superclass Agnatha
Jawless fishes have no true teeth or jaws.
Their skeletons are made of fibers and cartilage.
They lack vertebrae, and keep their notochords as
adults.
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Groups of Fishes
Modern jawless fishes are divided into two classes:
lampreys and hagfishes.
Lamprey
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Groups of Fishes
Class Cephalaspidomorphi
Lampreys are typically filter feeders as larvae and
parasites as adults.
Adult lampreys attach themselves to fishes, whales,
and dolphins.
They scrape away at the skin with small tooth-like
structures that surround the mouth and with a strong,
rasping tongue.
The lamprey sucks up the tissues and body fluids of
its host.
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Groups of Fishes
Class Myxini
Hagfishes have pinkish gray, wormlike bodies and four
or six short tentacles around their mouths.
They lack eyes, but have light-detecting sensors
scattered around their bodies.
They feed on dead and dying fish by using a toothed
tongue to scrape a hole into the fish’s side.
They secrete incredible amount of slime, have six
hearts, an open circulatory system, and regularly tie
themselves into knots.
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Groups of Fishes
Sharks and Their Relatives
The class Chondrichthyes contains sharks, rays,
skates, sawfishes, and chimaeras.
The skeletons of these fishes are built entirely of
cartilage.
Most cartilaginous fishes have tooth-like scales
covering their skin, making I as rough as sandpaper.
Many sharks have large curved tails, torpedo-shaped
bodies, pointed snouts with the mouth underneath,
and thousands of teeth arranged in several rows.
Most species of sharks do not attack people.
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Groups of Fishes
Some skates and rays feed on bottom-dwelling
invertebrates using their mouths as powerful vacuums.
The largest rays eat floating plankton.
Skates and rays glide through the sea with flapping
motions of their large, wing-like pectoral fins.
Many skates and rays cover themselves with sand and
rest on the ocean floor.
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Groups of Fishes
Bony Fishes
Class Osteichthyes
Their skeletons are made of hard, calcified bone.
Almost all living bony fishes are ray-finned fishes.
“Ray-finned” refers to the slender bony spines, or
rays, that are connected by a thin layer of skin to form
the fins.
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Groups of Fishes
Only seven living species of bony fishes are not
classified as ray-finned fishes.
These are the lobe-finned fishes, a subclass that
includes lungfishes (freshwater) and the coelacanth
(saltwater).
The fleshy fins of lobe-finned fishes have support
bones.
Some of these bones are jointed, like the arms and
legs of terrestrial vertebrates.
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Ecology of Fishes
Some fishes spend most of their
lives in the ocean but migrate to
fresh water to breed. These fish
are called anadromous.
Salmon, lampreys, and sturgeons
are anadromous.
Some fishes spend most of their
lives in the freshwater but migrate
to saltwater to breed. These fish
are called catadromous.
European eels are catadromous.
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