Chapter 19

Fish

Fish outline

• 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 tailThe largest part of the body is the

trunkThe 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

unpairedincludes 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. waterproof2. protection from parasites3. 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 types1. Skeletal2. smooth3. 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 stomachOral 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

• 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.