Fish

The most diverse and successful vertebrates

Three Classes of Fish

• Cephalaspidomorphi:

jawless fish,

lampreys

​

​

• Condrichthyes: cartilaginous fish, sharks and rays

​

​

• Osteichthyes:

bony fish

Characteristics of Fish

• Gills
• Two-chambered heart
• Sexual reproduction
• Most have paired fins
• Sensory systems
• Scales
• Jaws
• Separate flexible vertebrae
• Swim Bladders

External Anatomy of the Fish

Gills

• Feathery gill filaments
• Contains tiny blood vessels
• Water enters mouth, passes over gills and out through slits at side.
• O₂/CO₂ exchanged in capillaries.

Two-chambered heart

• One chamber receives deoxygenated blood from body
• The other pumps blood to the gills, where it picks up oxygen and releases CO2.

Sexual Reproduction

• Most have external fertilization
• Female lays a large number of eggs and then male deposits sperm on top of them

​

Adult male and female salmon spawn together in gravel beds of rivers and streams. Using sweeping movements of her tail, the female salmon digs out a gravel nest, called a redd. The male fertilizes the eggs as the female deposits them. The female protects the redd for one to two weeks or as long as she is able before dying.

​

Sharks

Some (sharks) have internal fertilization. There are three ways that sharks can be born:

• eggs are laid (like birds)
• eggs hatch inside the mother and then are born
• Shark pups grow inside the mother (like humans)

Mollies and guppies

• Internal fertilization.
• Eggs hatch inside and babies are born fully developed.

Mouth brooding Cichlids

• Care for young after hatching.
• The cichlid scoops eggs, and later, babies into mouth to protect from danger

​

​

Paired Fins

• Fan-shaped membranes attached to endoskeleton
• Used for balance, swimming and steering

Mandarin fish fin Longnose Gar fin

Sensory Systems

​

Sharks can use smell to follow a trail of blood for several km

Lateral line system

Fluid filled canals along sides of fish that detect movement and vibrations in water

Scales

• Thin bony plates formed from skin
• Growth rings can indicate age

Top: Broadnose shark, Bottom: Florida gar

Jaws

• Very important adaptation
• Allows grasping and crushing of prey

​

• Above: barracuda
• Right: pirrhana

Jaws in �Cartilaginous and Bony Fish

Jaws of Sharks

• Six to 20 rows of replaceable teeth which face backwards to prevent the escape of prey

Swim Bladder

Internal sac that fills with oxygen and/or nitrogen and controls depth through the regulation of gases in bladder.

Sharks have no swim bladder

Lungfish

Modified swim bladder allows the lungfish to breath air in low oxygen water.

Vertebrae

• Fish were the first to develop a backbone with vertebrae.
• Vertebrae provide support and flexibility

​

Three Classes of Fish

• Cephalaspidomorphi: jawless fish, lampreys
• Class Condrichthyes: cartilaginous fish, sharks and rays
• Osteichthyes: bony fish

Cephalaspidomorphi: jawless fish �

• Cartilage skeleton
• Parasitic bloodsuckers

Lamprey

• Sucker-like mouths
• Attach to another fish, scrape away flesh and then suck blood.

​

H�a�g�f�i�s�h

• Slit-like, toothed mouth
• Drills holes and sucks blood of dead or dying fish

​

Skin excretes mucous to make the fish slippery to predators. One hagfish can produce enough slime to fill a milk jug�

Slime gland pores that produce mucus on skin

​

Chondrichthyes: �Cartilaginous fish

• Entire skeleton is made of cartilage
• Include:
• Sharks
• Rays
• Skates

Sharks

Sharks

• Have been around for 400 million years
• Almost unchanged for 150 million years

​

Shark Teeth

• Bites prey, then tears it apart by tossing head back and forth
• Rows of backup teeth replace lost ones
• May grow and use 20,000 teeth in a lifetime

​

5 Most Dangerous Sharks

• Great White
• Tiger
• Mako
• Whitetip
• Bull shark

​

​

Great White Shark

• Up to 3000 teeth at one time
• Up to 23 feet in length
• Feed on sharks, sea lions, fish, rays, whales
• Account for 1/3 to ½ attacks on humans

Tiger Shark

Will eat fish, turtles, crabs, clams, mammals, sea birds, and other sharks. Occasionally Attack humans.

Mako Shark

• The fastest shark, and among the fastest fish
• Feed on schooling fish
• Dangerous, with many attacks on people

​

Bull Shark

• Because it is aggressive and swims in shallow water, is frequent attacker of people
• Swims close to shore and can live in fresh water rivers and lakes for awhile

Whitetip Shark

• Named in killings of shipwrecks

Hammerhead Shark

• From 12 – 20 feet long
• Unlike other sharks, they form schools

Whale Sharks�

• Largest sharks AND largest fish
• Up to 46 feet long and 15 tons
• Filter feeders – eat mostly plankton and krill

Senses

• Over 2/3 of a shark’s brain is dedicated to smell
• Can feel vibrations in the water

​

• Sharks can use smell to follow a trail of blood for several km

​

Rays

• Flat bodies
• Broad pectoral fins on sides
• Glide by flapping fins
• Feed on mollusks and crustaceans on ocean floor

Offenses and defenses

• Sharp spines with poison glands.
• Electricity to kill predators and prey.

Above: electric ray; Right, top: stingray barb; right: barb in foot

Skates

Skates

• Stocky tail with no stinging spine
• Two lobes on pelvic fin
• Thorn-like scales on midline of back and tail

Rays

• long tail with stinging spine at midway
• Single lobes on pelvic fin
• No thorn-like scales

Osteichthyes – �Bony Fishes

• The largest group (superclass)
• Skeleton is made of bone
• Three classes:
• lung fish
• Lobe-finned fish
• Ray-finned fish

Bony Skeleton

​

• Skeleton of bone, not cartilage
• Bony skeleton allowed evolution of land animals

Lung Fish

• Gills and lungs (modified swim bladder)
• Can live in oxygen- poor water by
• gulping air from surface
• burrowing in mud and breathing through skin during drought

Lobe-finned Fish

• Only one species: the coelacanth
• Fins adapted to crawling
• Pre-cursor to amphibians

Coelacanth

• Scientists thought the coelacanth had gone extinct with the dinosaurs.
• 1938: a specimen was found at a local fish market
• Scientists now know that the coelacanth has remained alive, and unchanged for 400 million years.

Ray-finned Fish

• Fan shaped fins with stiff spines (rays)
• Fins adapted to swimming
• Huge diversity: Catfish, salmon, perch….

​

Ray-finned fish that can walk on land

• Walking catfish
• Mudskipper

​

​

Inflatable Fish

Porcupinefish:

• When threatened, swell by filling body with water
• Become too large for the predator to swallow.
• Spiny covering is another defense.

​

Pufferfish:

• Inflates when threatened
• Large black spot near the tail draws predator’s attention away from the its head and allows escape.

Toxic Fish

The Beautiful Lionfish:

• Sharp spines are coated with a poisonous mucous
• Capable of delivering a painful sting.
• The venom of some is strong enough to kill a man.

​

The Ugly Stonefish:

• stone-like appearance is an excellent camouflage
• Has sharp, venomous spines that contain enough poison to kill a man.

Sea Horses

• Male seahorses carry fertilized eggs in a special abdominal pouch until they hatch.
• each day a seahorse can consume up to 3,000 brine shrimp
• seahorses have no teeth and swallow their food whole

Seahorse Anatomy

coronet: is nearly as distinctive as a human thumbprint�dorsal fin: moves fish forward�pectoral fins: control turning and steering�eyes: each eye moves independently�

Dangerous Fish

Moray Eel:

• one of the largest eel species.
• feed mainly on fish.
• razor sharp teeth
• can remove the fingers of divers.

​

Electric Eels:

• Electric eels are not true eels. They are related to catfish and carp
• found in South America.
• Electric eels produce more electricity than any other living creature.
• Can disable a cow, stun a man or horse, light a neon lamp, or drive a small motor.

Hidden Fish

Leafy Sea Dragon:

• species of seahorse
• camouflaged by leafy extensions which resemble seaweed.
• feed mainly on small shrimps

​

Scorpionfishes:

• camouflaged by bizarre appearance
• Use camouflage to ambush prey
• numerous venomous spines cover their bodies.

Fish that ‘fish’

Frogfish:

• camouflaged by appearance.
• modified dorsal spine with a fleshy growth at the end.
• lie motionless and use this spine like a fishing rod.
• curious fish are swallowed up by large, powerful jaws.

​

Anglerfish:

• lives deep on the ocean floor
• eats crustaceans and smaller fishes.
• uses a bioluminescent lure on the end of its "fishing pole".
• Lure resembles bioluminescent bacteria which other fish eat.

Above: frogfish;

Left and below: anglerfish

Flying Fish

Flying Gurnards

• large, wing-like pectoral fins.
• do not actually fly.
• Their large fins help them to swim low over the sand as they search for food.

Atlantic Flying Fish

• large pectoral fins and long tail fin
• "leap" or "glide" like flying squirrels over the water surface.

Deep Ocean Fish

Angler fish, Hatchet fish, viper fish

Luminescence in the Deep

-Bioluminescence is light produced by a chemical reaction which originates in an organism. �-Very common in the ocean

Warty Anglerfish with a luminescent lure; Deep-sea lizardfish with luminescent eyes

Orange Roughy�

• Live to be 150 years old
• Don’t reproduce until 25 or 30 years old
• Live up to one mile deep

Megalodon