Marine Fishes
Chapter 12
General Info on Fish
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They are the most common and diverse group of
animals with backbones in the ocean and in the world
They are an ancient group – their origins date back more
than 500 million years
There are about 20,000 different species of fish found
worldwide in both marine and freshwater ecosystems
They appear in a wide variety of shapes, sizes, colors
Protochordates and Jawless Fishes
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Animals with backbones (spinal chords) are called
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Fish have a hollow, dorsal nerve chord called a
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chordates
notochord
A notochord is a flexible, rodlike structure that supports
the spinal chord
Protochordates are organisms that have a
notochord, but lack certain advanced structures that
other fish have, so they are called primitive chordates
Protochordates and Jawless Fishes
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Fish that are higher chordates are also the first
vertebrates
Vertebrates are animals characterized by having a
skeleton, backbone, skull and brain
The higher chordates include all the vertebrates – fish,
amphibians, reptiles, birds, and mammals
Protochordates are interesting to
scientists because their ancestors seem to
represent the evolutionary link between
invertebrates and vertebrates!
Jawless Fishes
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Most fish, as you can observe, have movable mouth
parts called JAWS
There are a few species of fish, however, that do not
Hundreds of millions of years ago, the oceans were
inhabited by jawless fishes
These were the first types of fish to evolve
Jawless fishes are the most primitive of the
vertebrates because they have no jaws and don’t
have a true backbone
Jawless Fishes
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There are only 2 types of jawless fishes alive today
They are the hagfish and the lamprey
They are in a class called Agnatha (it means “without
jaws”
Some can grow up to 1m in length
These fish live as parasites
The lamprey inhabits estuaries from Maine to Florida
It uses a sucking disk on its mouth to attach to living
fish in rivers
It feeds by using its teeth and rasping tongue to make a
hole in the body of the host fish
The lamprey then sucks blood out of its tissues
Hagfish
Lamprey
Cartilaginous Fish
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Feel the tip of your nose and your ears. Go ahead,
I’ll wait!
They feel soft because they are made from cartilage, a
flexible connective tissue made of cells and protein
Cartilaginous fishes have bodies whose entire
skeletons are made of cartilage
They are in the class Chondrichthyes (it means
“cartilage fishes”
This class include such fishes as sharks, skates, and
rays
Whale Shark
Great White Shark
Tiger Shark
Skates
Rays
Characteristics of Cart. Fish
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There are fewer than 700 species, as opposed to more
than 25,000 species of bony fish
These were the first jawed fish to evolve
Cart. Fish have placoid scales, which are actually
tiny teeth that are deeply embedded in the skin (and
they point backwards)
If you were to pet a shark from head to tail, it would feel
like rough sandpaper
However, I strongly suggest that you NEVER attempt to
“pet” a shark!
Cart. Fish have visible gill slits for breathing,
while bony fish have theirs concealed by a skin
flap
Skates and Rays
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Most are bottom dwellers
They have very well developed pectoral fins
The up and down movements of these fins resemble the
wings of a bird in flight
Stingrays are often found concealed in the sands of the
Gulf of Mexico and along the Atlantic coast from the
Carolinas to Brazil
A sharp spine near the base of its tail can inflict a
painful, sometimes deadly stab wound
R.I.P. Steve Irwin!
Sharks!
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There are about 350 known species of sharks
The smallest is the pigmy shark, which is about
25cm long
The biggest shark (in fact, the biggest fish) is the
whale shark, which can be more than 15m in length
The whale shark is harmless because they are filter
feeders that consume plankton
Some sharks are bottom dwellers that have crushing
teeth and eat mollusks
Nurse sharks and leopard sharks are examples of
this
Shark Anatomy
Shark Internal Anatomy
Nostrils
Mouth
Heart
Gall Bladder
Testis
Liver
Pylorus
Gill Slits
Pectoral Fin
Liver
Stomach
Spleen
Spiral Valve
Intestine
Pelvic Fin
Claspers
Rectal
Gland
Nurse Shark
Leopard Shark
Great Whites
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This is one species of shark that can be dangerous to
humans
Though it feeds on marine mammals such as seals and
sea lions, great whites have attacked and killed
humans before
The biggest great whites ever caught weighed over
1200kg and measured from 5 to nearly 6.5m long
While great whites have killed humans in the past, these
deaths are “accidental” in nature
What do you think this means?
Sharks
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Other sharks that have killed humans are the
tiger shark, the bull shark, and the hammerhead
Tiger sharks prey on sea turtles, seals, and other smaller
sharks
Bull sharks are an aggressive species of shark that are
found in some freshwater areas as well
Hammerheads have 2 lateral projections on their
heads with eyes at the end
The more predatory sharks like these have
sharp, serrated teeth for catching and
cutting up their prey
Bull Shark
Sharks
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Sharks have been on this planet for more
than 300 million years
They closely resemble their ancestral
forms, and haven’t needed to evolve
They are sometimes called “evolutionary
dead-ends” or “living fossils”
What structures do they possess that have
allowed them to remain on this planet for
so long, never needing to change?
Shark Structures and Behavior
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Sharks have very sensitive receptors for the detection of
stimuli
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The lateral line organ, along each side of a sharks
body, can pick up sound vibrations over great distances
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The shark’s sense of smell is so sensitive and
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acute that it can detect a drop of blood nearly half a km
away
In fact, nearly 2/3 of a shark’s brain is devoted to its
sense of smell
Sharks also have receptors called ampullae of
Lorenzini in their snout – these can detect electric
fields given off by prey in their muscle movement
Shark Anatomy
Sharks
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After detecting prey, sharks are more than well
equipped to catch and eat them
Sharks can move very quickly through the water
because of their body shape
They also have several rows of sharp teeth – the rows at
times move forward to replace lost teeth
At any given time, sharks can have
hundreds of teeth in its mouth!
Great White Shark Teeth
Bony Fishes!
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More than 95% of all fish on Earth belong to the class
Osteichthyes (meaning bony fishes)
These fish have a skeleton of bone, rather than
cartilage
They have a backbone with a chain of vertebrae, just
like humans!
They are found in every type of aquatic
environment
They all have protective scales which are attached
loosely to the skin and may even rub off on your hands!
Fish feel slimy because they secrete a protective mucous
that helps fight infection, and also allows them to move
quicker through the water
Bony Fishes
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The gills of bony fish are located in the head region, on
either side of the body
The gills are covered with a flap of tissue called an
operculum, which opens and closes every time the fish
breathes
Fish breathe by taking water into its mouth
The water contains Dissolved oxygen, and the
water moves from the mouth over the gills
The gills have filaments attached to them that
allows the oxygen to diffuse into them
The DO is then passed into the blood
Bony Fish
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One of the defining characteristics of fish is the fact that
they have fins
These are mainly used for swimming, and any
marine animal that has the ability to swim is called
nekton
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Swimming can be tiring, so fish need the ability to be
able to rest – to float in place
They do this by a gas filled organ called a swim
bladder
By regulating the volume of gas in its swim
bladder, a fish can rise, sink, or stay in position in
the water
What is the ability to stay afloat in water called?
Interesting Fish Facts
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Fish have been on the earth for more than 450
million years
Eggs of Seahorses are fertilized and reared by the
males!
Some fish like sharks don't posses an air bladder to help
keep them afloat and must either swim continually
or rest on the bottom
Fish feel pain and suffer stress just like mammals and
birds
Tropical fish are one of the most popular pets in the U.S.
Every year, fish scales grow and growth rings are
produced – so you can tell how old a fish is by counting
the rings! (just like with trees)