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Chapter 19
Fish
Fish outline
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Diversity of species
Bony fish
Anatomy and Physiology of bony fish
Special organs of bony fish
Spawning
Parental care
Cartilaginous fish
Diversity of Species
Fish are cold-blooded, water-dwelling vertebrates with gills
and scales.
There is more variety among fish than all other land and
water vertebrates combined!!!
Bony Fish
“Osteichthyes”
• Skeleton made of partially or wholly bone
• The most abundant fish – 95% of all known fish
• Goldfish, cod, catfish, bass, salmon, tuna, and many
others!
Structure of Bony Fish
• Three main body regions:
head, trunk, tail
• Features of the head
nostrils – used for smell
for taste, the taste buds are spread
over the body of the fish
gills – covered by gill coverings known
as opercula, which
protect the gills.
Structure of Bony Fish
• Features of the trunk and tail
The largest part of the body is the trunk
The most prominent features on the trunk and
tail are the fins
The fins are called “rayed fins” due to the
webbing
Most have two sets of paired fins – the
pectoral fins and the pelvic fins
Structure of Bony Fish
• Most also have vertical fins which are unpaired
includes the dorsal fin
the anal fin
the caudal fin – tail
• Skin and Scales
most have a tough skin
the skin has mucus cells which make the fish
slippery
the skin has chromatophores which give it color
Skin and Scales
• Most bony fish have fairly tough skin
• The skin contains mucous cells to make the fish slimy –
and gives the fish their “fishy” smell
• The mucous serves three purposes:
1. waterproof
2. protection from parasites
3. reduction of friction as it moves in water
Skin and Scales
• Many contain Chromatophores – cells that give the fish
its color
• Many have scales
• Scales do not increase in number as the fish grows – the
scales simply grow larger
• The scales of many fish even have growth rings – which
aid in determining the age of a fish
Skeleton
• Backbone – contains individual vertebrae of bone or
cartilage
• Backbone – also has spine-like extension
• Cranium – encloses the brain
• Pectoral girdle and pelvic girdle – support the fin
Muscles
• Has all three of the basic muscle types
1. Skeletal
2. smooth
3. cardiac
• Cardiac – heart
• Smooth – digestive organs
• Skeletal – “fleshy” part of the fish – the part you eat
Muscles
• Unlike vertebrates, a fish skeletal muscles are arranged
in “W” shaped bands
• Myomeres – what the “W” shaped bands are called
• Each myomere is controlled by a separate nerve, allowing
the fish to move through the water in wavelike motion.
Respiratory System
• Fish breathe right in the
water
• Gills – A fish can extract
80% of the oxygen from
water – people only get
about 25%
• Protecting the gills –
They are covered by a
wide plate of bone
(operculum)
Respiratory System
• Fish are continually allowing
water to “rake” over their gills as
they “inhale”
• If the fish is still it uses its
mouth
• If swimming, the water flows into
the mouth and out the gills
• Some sharks can only breathe by
moving
Circulatory System
• The circulatory system is closed, consisting of arteries
and veins similar to mammals
• Fish have no lungs – as a result the circulatory system
is quite simple
• The fish has a two chambered heart
• Blood flows from the heart to the gills
• After oxygen is in the blood from the gills, the blood
moves to the body
• The blood then returns to the heart to be pumped back
to the gills for more oxygen
Digestive and Excretory Systems
• The most numerous of all fish are plankton-eaters
• The carnivores are less numerous, but have more variety
• The carnivores may eat insects to other fish
Digestive and Excretory Systems
• From oral cavity to stomach
Oral cavity (sometimes with teeth) → pharynx →
esophagus → stomach
• Digestion – food is mostly digested in the stomach
• Digested food then passes through the intestine
• Waste exits the anus near the anal fin
Digestive and Excretory Systems
• Excretion of liquid waste
Freshwater fish are
continually taking in extra
water and therefore must
produce a lot of urine.
Saltwater fish are
continually losing water
and therefore must ingest
large quantities
Nervous System
Senses of the fish
• A typical bony fish has very good eyesight
• It has no eyelids
• They focus by changing the shape of the eye
• Most fish can hear very well
Nervous System
• Fish can sense faint vibrations and pressure changes
by its “lateral line”
• Lateral line – a system of nerve endings that
extend over its head and sides
• The lateral line allows it avoid obstacles or
predators
• Fish have excellent sense of smell
Reproductive System
• In both sexes, sex cells (eggs and sperm) are released through
the urogenital openings.
• Most bony fish reproduce by external fertilization – eggs are
fertilized outside the body of the female.
• When fish are ready to spawn (lay eggs) they may congregate
or migrate to the place they were hatched.
• The eggs (called roe) are laid in the water by the female .
• The male releases “milt” which contains the sperm.
• Once fertilized the egg begins to develop into a young fish
Reproductive System
• Most fish protect their nest of eggs and then the young fish
after they are born.
• The young fish (called a “fry”) is large enough to find its own
food when hatched.
• A female may lay as many as a million eggs, but only a fraction
of them survive and hatch and produce fry.
Special Organs
• Swim Bladders – a hollow gas-filled chamber located near the
top of the bony fish.
• It allows the fish to become stationary.
• The swim bladder is filled with gases by a special “gas gland”.
• Not all fish have a swim bladder.
Special Organs
• Light and electricity generating organs.
• Many deep sea fish have light organs that enable them to see
in the murky depths.
• The electric eel can generate electricity and can deliver a
discharge of 600 volts.
The Cartilaginous Fish
• There are two classes of Cartilaginous fish
– Class Chondrichthyes: Sharks, rays, and chimaeras
– Class Cyclostomata: Lampreys and hagfish
Class Chondrichthyes
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Sharks, rays, and chimaeras
Only 3% of all fish
All have jaws and cartilaginous skeletons.
They are all covered with “tooth-like” scales that make the
fish feel as though covered in sandpaper.
Sharks
• Sharks lack a swim bladder
• They have a complex reproductive system – they give birth to
live young.
• Due to a lack of swim bladder, sharks must continually move and
some never sleep because of this.
• Sharks have the best sense of smell of all fish.
• Attacks on humans are rare.
Rays
• Rays have large flat bodies and whip-like tails
• The most dangerous ray is the stingray which is responsible for
more injuries to humans than all other fish combined!!!
• The largest is the manta rays – a gentle giant – it can grow
up to 25 feet!
Chimaeras
• Chimaeras – also known as the elephant fish
Lampreys and Hagfish
• Lack jaws
• Make up less than 1% of all fish.