Classification of the Major Taxa of Fish

Station 1. Fish Diversity
Classification of the Major Taxa of Fish
! Phylum Chordata examples
! Subphylum Vertebrata
! Supraclass Agnatha jawless fishes
! Order Osteostraci
! Order Anaspida
! Order Heterostraci
! Order Coelolepida
! Order Cyclostomata
! Class Myxinoidea hagfish
! Class Petromyzontida lampreys
! Class Placodermi
! Order Arthrodiriformes
! Order Antiarchiformes
! Supraclass Gnathostomata jawed fishes
! Class Chondrichthyes
! Subclass Elasmobranchii
! Order Cladoselachiformes extinct Paleozoic sharks
! Order Xenacanthiformes Paleozoic freshwater sharks
! Order Selachii typical sharks
! Order Batoidea skates and rays
! Subclass Holocephali
! Order Chimaeriformes chimaeras or ratfishes
! Class Acanthodii various extinct fishes
! Class Osteichthyes higher bony fishes
! Subclass Actinopterygii ray-finned fishes
! Infraclass Chondrostei sturgeon, paddlefish; primitive ray-finned fishes
! Infraclass Holostei gars, bowfins; dominant ray-finned fishes of Mesozoic
! Infraclass Teleostei most bony fish; dominant in Cenozoic and recent times
! Subclass Sarcopterygii lobe-finned fishes
! Order Crossopterygii ancestors of land vertebrates
! Order Dipnoi lungfishes

Station 1. Fish Diversity
CLASS: AGNATHA
JAWLESS FISHES
includes the living forms LAMPREYS and HAGFISHES, and several
extinct forms
The jawless fish (supraclass Agnatha; a = without, gnathos = jaws) include the extinct
ostracoderms and the living lamprey eels and hagfishes. Ostracoderms, the earliest
known fossil chordates, have been found in the rocks of the Ordovician, Silurian and
Devonian periods, These jawless fish were small, armored, bottom-dwelling freshwater
filter feeders. The head was covered with thick bony plates, and the trunk and tail were
covered with thick scales. Ostracoderms had median fins; some species had paired
pectoral fins.
The living relatives of the Ostracoderms are the lampreys and hagfishes. These
animals have cylindrical bodies up to a meter long supported by a cartilaginous skeleton.
Their smooth skin lacks scales, and they have neither jaws nor paired fins. Most hagfish
eat worms and other invertebrates, which they burrow for or prey on dead and disabled
fish.
lamprey
hagfish

Station 1. Fish Diversity
CLASS: PETROMYZONTIDA
Relevant features:
nostril!
olfactory!
organ!
pineal eye!
brain!
dorsal!
aorta!
digestive!
pharynx!
LAMPREYS
•! anadromous and freshwater; cool zones of world
•! one or two dorsal fins are present
•! eyes well developed
•! dorsal and ventral nerve roots separated
•! sucking mouth; barbels absent; rasping teeth on oral disc and tongue
•! small cerebellum
•! sexes separate
•! eggs small, not yolky, occurring in the thousands; larval stage
undergoes radical metamorphosis in fresh water
•! die shortly after spawning
horny !
teeth!
sucking !
mouth!
rasping !
aortic !
tongue!
arches!
ventral!
aorta!
breathing!
pharynx!
gill !
slit!
pericardial!
cartilage!
ventricle!
nerve !
chord!
atrium!
notochord!
liver!
intestine!
peritoneum!
Lamprey structure
gonad!
coelom!
European river lamprey, Lampetra fluviatilis
mouth !
opening!
•! parasitic (freshwater or anadromous) or non-parasitic (only freshwater)
tongue!
disc!
teeth!
infra-oral!
tooth plate!
Oral disc and teeth of lamprey

Station 1. Fish Diversity
CLASS: MYXINI
Relevant features:
HAGFISHES
A polybranchiate hagfish, Eptatretus stoutix
•! marine; temperate zones of the world
•! no cerebellum
•! eyes are degenerate, lens absent
•! barbels present around biting mouth
•! teeth only on tongue plus one on palate
•! the dorsal fin is absent; the caudal fin extends
onto part of the dorsal surface
•! dorsal and ventral nerve roots united
•! numerous mucus pores along body expel a slimy substance (hence nickname “slime eels”), for
feeding and defense
•! can go through knotting movements to free themselves from entanglement and own slime
•! ovaries and testes in same individual, but only one functional (not hermaphrodite)
•! eggs large, yolky, up to 30 per individual; no metamorphosis
•! the external nasohypophysial opening is terminal, and it is through this opening that respiratory
water passes backward to the gills (unlike lampreys)
•! scavenger feeders, mostly eating dying or dead invertebrates and other fishes
•! only vertebrate in which the body fluids are isosmotic with seawater

Station 1. Fish Diversity

Station 1. Fish Diversity

Station 1. Fish Diversity
CLASS: CHONDRICHTHYES
Relevant features:
•! marine, though some in deltas or freshwater
•! cartilaginous skeleton
•! five to seven gill slits
SHARKS
•! shark skin made up of denticles (placoid scales) for protection
and for increased hydrodynamics
•! lack swim bladder, so need to keep swimming to
avoid sinking
•! most are predatory, but some are filter feeders of plankton
•! large olfactory bulb for excellent smelling
•! efficient intestine with spiral structure
•! internal fertilization
•! most bear live young
•! replaceable teeth in multiple rows along edges of upper
and lower jaws, moving forward as needed.
•! lower teeth are primarily used for holding prey, while the
upper ones are used for cutting into it.!
lower!
upper!
side!
front!
Examples of Shark Teeth!
upper!
second !
dorsal fin!
claspers!
(male)!
Spiny Dogfish! White Shark! Thresher Shark! Hammerhead Shark! Tiger Shark!
lower!
upper!
lower!
upper!
lower!
Shark skin denticles!
seminal !
vesicle!
anus!
cloaca!
first!
dorsal fin!
pelvic fin!
Make sure to!
look in microscope !
to see shark skin !
denticles up close!
pectoral fin!
vas deferens!
lateral line!
testis ! vertebrae!
stomach! gall !
intestine!
bladder!
external gill !
opening!
brain!
heart!
gills!
rostrum!
nostril!
mouth!
olfactory !
bulb!

Station 1. Fish Diversity
lower!
CLASS: CHONDRICHTHYES
Sharks, Rays, and Skates
•! one of the two groups of true fishes (other is bony fish)
•! skeletons are made of cartilage, hardened by lime
•! about 600 species
•! mostly marine
•! most give birth to live young!
A skate egg case. These may be found
on almost any empty beach. Skates lay
eggs, each in a horning container, nearly
all year round. They hatch in 5 to 6
months. Egg cases vary in size from
about 3 to 6 in. long.

Station 1. Fish Diversity
CLASS: OSTEICHTHYES
Evolution of Bony Fishes
CHONDROSTEI
RAY-FINNED
FISHES
LOBE-FINNED
FISHES
Butterfishes
(Coelacanths)
Searobins
Flounders
Remoras
Gars
Filefishes Clingfishes
Toadfishes
Batfishes
Gobies
Mackerels
Blennies
Barracudas

Station 1. Fish Diversity
Bony Fishes
CLASS: OSTEICHTHYES
•! one of the two groups of true fishes (other is Chondrichthyes)
•! includes ray-finned fishes and lobe-finned fishes
•! about 30,000 species
•! live in any watery habitat
•! most are covered in scales
•! gills covered by flap
•! have swim bladder for buoyancy
•! usually lay eggs that are often fertilized externally
Spotted grouper
Clownfish fanning eggs
Black-tipped rock cod
Shown here are some members of the Serranidae
family of carnivorous saltwater fishes. This family
contains fish that are a valuable food source for
many human residents of the tropics and subtropics.

Station 2. Skeletal
THE SKELETAL SYSTEM
To the left is the skeleton of a gar or bowfin (Holostei) and to the right is a skeleton of
a perch (Teleostei). Teleosts have superior trophic and locomotor adaptations.
Look at the differences in the thickness of the bones and the structure of the jaws in
the two fish. Why do you think the Holosteans are more primitive?
Note that the Holostean has a more primitive firm biting jaw, while the perch has a jaw
specialized for suction feeding. Most teleosts feed by expanding the anterior bones
of the upper jaw to produce a strong suction force into the mouth. !
(Roi Holzman - UC Davis)
Suction feeding is perhaps the most common prey capture
strategy of fishes. During suction feeding, the predator
opens its mouth and rapidly expands its buccal cavity,
generating a flow field external to the mouth. The rapid
expansion of the buccal cavity produces high fluid
velocities and accelerations that persist only a short
distance from the mouth (about half of one mouth
diameter), and for a short time (a few ms). Therefore, the
predator must carefully time its strike to maximize the
forces exerted on its prey.!

Station 2. Skeletal
THE SKELETAL SYSTEM
Skeleton of a Teleost
Compare the skeleton of
this bony fish with that
of a mammal - the rat.
Unlike that of the skate,
note the interlocking
vertebrae of rat.
Though it lacks bones,
the vertebral column of
a skate shows
elaborate calcification.

Station 3. Jaws
The famous American Museum of Natural History
reconstruction of jaws of the giant fossil shark
Carcharodon megalodon. Overzealous preparators
in the museum’s Department of Vertebrate
Paleontology (shown framed by their handiwork in
a 1909 photograph) used the largest teeth they
could find to make the most spectacular jaw. In
living sharks, teeth diminish in size as they
approach the corners of the jaw, but the
preparators used teeth primarily from the anterior
positions of the upper jaw, much exaggerating the
final reconstruction. Estimates of the length of
Carcharodon megalodon have ranges from 60 to
100 ft.
JAWS
Compare the shark jaw with that of
the bony fish. The shark’s jaw is
made of cartilage. Now look at the
jaw of a skate, another cartilaginous
fish. Notice the difference in the teeth
of this animal that feeds on mollusks.
Like other sharks, this sand
tiger shark’s teeth fall out
when they become worn or
snagged on prey. Lost teeth
are quickly replaced by new
ones lined up right behind
the old ones.
A regression of tooth size on actual body length
for the living Carcharodon carcharias indicates
by extrapolation that Carcharodon megalodon
was “only” 43 ft in length! (Randall, J. E., Science,
181: 169-170.)

Station 3. Jaws
JAWS
The teeth of Elasmobranchs are modified placoid scales, and are continuously shed and replaced.
The teeth of bony fish resemble those of most vertebrates, and consist of dentin and enamel.
This jaw of a Port Jackson shark shows the distribution
and varieties of shark teeth. The placoid scales exhibit a
gradual transition to teeth as they approach the front of
the jaw.
This unerupted tooth of a garfish shows the
development of teeth in bony fish. Tooth germ is
a replacement for a tooth that will be shed.

Station 4. Locomotion
LOCOMOTION
Fish are superbly adapted to live in water. Water has main two features to which fish have had to
adapt.
1) Water is dense. It is about 800 times denser than air.
a) This affects fish by supporting weight well.
b) However, it also makes it harder for fish to breathe. Fish use 10% of its
energy ventilating its gills, whereas a human uses only 3% of its
energy to ventilate his lungs.
2) Water is incompressible. Any water particle that moves causes the particle next to it to
move as well. Fish have capitalized on this:
a) Their lateral line senses water movement and vibration. The lateral-line
system helps the fish to avoid collisions, to orient itself in relation to
water currents, and to locate prey.
The lateral line of a catfish!
b) When feeding, water, along with food, can be sucked into their mouth.

Station 4. Locomotion
An abbreviated
heterocercal
tail of a bowfin
A generalized
homocercal tail
(most bony fishes)
FISH TAILS
The tails of fishes reflect changes that have taken place through the ages. In sharks, as in early
fossil fishes, the upper part of the tail contains the
backbone and extends to a point. This asymmetrical
fin type is called heterocercal.
Homocercal tail of
a striped bass
A generalized heterocercal tail
(sharks, sturgeon, fossil fishes)
In modern bony fishes, the tail is more balanced and the
backbone ends where the tail begins. This type of caudal fin is
called homocercal. The fin is external to the muscle mass of the
body and is very flexible. Lateral undulation of the tail produces a
symmetrical force so that, together with a well controlled air
bladder, a teleost can swim horizontally without continuously employing its paired fins, reducing
drag. Relieved of this function, the paired fins of teleosts
became more flexible and diverse in size, shape, position.
There is hardly a function for which teleost fins have not
become adapted - from food getting to love making, from
sound production to walking, and even flying. !

Station 4. Locomotion
FISH TAILS
Another type of tail is called diphycercal or isocercal. In this type of
caudal fin, the vertebrae extend all the way to the end of the tail. It is
present in coelacanth and lungfish, where
it is three-lobed. It may be secondarily
isocercal tail
of a cod
acquired from the homocercal condition by loss of the real caudal fin
and the gaining of a new one from dorsal and anal elements.
Isocercal tail of
a coelocanth
A protocercal type of caudal fin extends around the vertebral column. It is present in embryonic
fish and in hagfish.
protocercal tail of
a hagfish

Station 4. Locomotion
BUOYANCY
How do fish overcome gravity? Fish will sink unless they either have some kind of float or they
produce vertical lift by propulsive movements.
In the first case, neutral buoyancy is found in most bony fishes in the from of a swim bladder.
The swim bladder is gas-filled and lies below the vertebral column. Though cartilaginous
fishes lack a swim bladder, some have a large fatty liver that provides some buoyancy.
Many pelagic (deep sea) fishes like tuna, mackerel, swordfish, and the cartilaginous fishes
lack swim bladders. These fishes must swim constantly in order to produce
sufficient lift. This is done by extending the pectoral fins like wings,
with forward thrust provided by the caudal fin. The dorsal and ventral
fins reduce the tendency to roll and yaw. They also assist in turning
movements. The pectoral and pelvic fins act as hydroplanes and
control the pitch. The tail fin contributes to the forward thrust.
Compare the forces associated with a fish swimming and a bird flying.
Yaw
FISH BIRD
GRAVITY Center of
Pitch
Roll
gravity
Center of
gravity
DRAG THRUST DRAG
THRUST
LIFT and
BUOYANCY
Keel
Lateral
propulsive motion
Yaw
Pitch
Vertical
propulsive
motion
GRAVITY
LIFT
Roll

Station 4. Locomotion
Groupers often weigh hundreds of pounds. Yet, the buoyancy of
water and the fish’s swim bladder allow it to hover as if weightless.!

Station 4. Locomotion
SHARK SKIN
Features of shark skin itself improves the hydrodynamics of
this swimmer. Shark skin is made of tiny, hard, tooth-like
structures called dermal denticles or placoid scales. These
structures are shaped like curved, grooved teeth. Like teeth,
they have an outer layer of enamel, dentine and a central pulp
cavity. Unlike the scales of bony fish (ctenoid scales) that get
larger as the fish grows, placoid scales stay the same size. As
the shark grows, it just grows more placoid scales.
These scales also help the shark swim more quickly because
their streamlined shapes reduces drag by channeling it
through grooves. All of the spines of the denticles point
backwards (towards the tail), so it feels relatively smooth if you
move your hand from head to tail, but rough the other way.
SHARK SKIN TECHNOLOGY
Because of its usefulness in improving hydrodynamics, engineers have
developed several products modeled on the shark skin. Special “Sharkskin”
swim suits havebeen developed by Speedo to give Olympic swimmers
a competitive advantage.
Shark placoid scale!
Cal Olympian Natalie Coughlin
wearing a Sharkskin swimsuit
The US Navy has even developed a special coating to put on their ships that mimics shark
skin. It reduces the amount of algae and barnacle buildup that accumulates on ships in dock,
which reduces drag and therefore fuel usage.

Station 5. Fish Oddities
FISH ODDITIES
“Warm-blooded”
Tuna and pelagic shark have
musculature 10 degrees warmer than
the surrounding sea.
Changing sex
Most reef fishes can change
their sex. There are many
different patterns for sex
-change. Some species will
begin life as males and switch
to females (protandry), and
others switch from female to
male (protogyny). Further still,
some will change sex in both
directions, and others will be
both sexes at the same time.!
Flying fish
A flying fish leaves the water with
outstretched pectoral fins which, held
rigid, will serve as wings during a
prolonged, 35 mile-an-hour glide. Prior to
flight, the tail served as a miniature
outboard motor, beating back and forth
as much as 50 times a second and
helping lift the fish into the air. Flying
fishes use their aerial skills as a way of
escaping from their enemies.
Big Mouth
The mouth of the carnivorous leaf fish of the
Amazon basin is well suited to satisfying its
voracious appetite and its habit of yawning.
From a normal position, the mouth can shoot
forward to from a tube that sucks in tiny victims
with the efficiency of a vacuum cleaner. In
captivity a two inch leaf fish consumes at least
1,000 one inch guppies each year.
Scaleless
Catfish possesses no scales. Their bodies are
either naked or covered in bony plates called
scutes. In some species, the mucus-covered
skin is used for cutaneous respiration.!

Station 5. Fish Oddities
DEFENSE and PREDATION
Porcupinefish (above) and Burrfish (below)
are closely related to the puffers, but in
addition to their ability to swell, their skin is
covered with stout spikes that make them
more dangerous to other fishes and hard to
handle. These are tropical fishes, usually
found in shallow water where they feed on
small invertebrates.
An active huntsman,
the archerfish fires
water at an insect by
compressing its gill
covers and forcing
the water through a
tiny tube formed by its
tongue and palate.
The archer’s
accuracy is more
amazing since it aims
from under water and
compensates for
refraction. !
Sargassumfish are
small anglers that
live in the floating
sargassum (a
macroalgae) beds
of the warmer
Atlantic. Their color
and adaptations,
such as the armlike
pectoral fins,
enable them to
thrive in this limited
environment.!

Station 5. Fish Oddities
Fewer fins
Some fish have lost one set of fins,
whereas others, like the eel, have no fins.!
FINLESS FISH
Among the almost 600 species of eels are morays.
Moray eels live along rocky coasts or near the ocean
bottom in coral reefs. Some moray eels are fierce
looking, especially the large ones that can grow up to ten
feet long and weigh 75 pounds. They have powerful jaws
and long, needle-sharp teeth. Their thick skin is covered
with mucus instead of scales. The mucus protects it from
scrapes as it moves about searching for prey in cracks
and crevices of the coral reef. !
Garden eels live on the sandy ocean floor in shallow water. They
are shy creatures, and they live together in colonies in a very
unusual way. Each eel burrows tail-first into the sand and lives in
the burrow. When hungry, the garden eels come out of their
burrows and, standing upright on the tips of their tails, swoop
gracefully to catch fish eggs and tiny animals that float by. !

Station 5. Fish Oddities
CAMOUFLAGE
The blenny (above) and pricklebacks
(right) live along coastlines, where they
often hide in holes in rocks. The weird
plant-like objects on their heads are
actually flaps of skin that help to
camouflage them.!
The leafy sea dragon lives in the temperate, shallow waters
of southern and western Australia. Their leafy protrusions
serve as camouflage among the seaweed.!

Station 5. Fish Oddities
If you look closely at the picture of the waving
sea grasses, you will spot some thin bay
pipefish. !
CAMOUFLAGE
A flounder blends into the sandy sea floor. !

Station 5. Fish Oddities
WALKING FISH
The mudskipper and the walking
catfish spend more time out of the
water than in, and the Australian
lungfish drowns if kept under water.
Australian lungfish
Mudskippers (in the Goby family) are uniquely adapted to a completely amphibious lifestyle. Mudskippers are quite
active when out of water, feeding and defending their territories. They have several anatomical and behavioral
adaptations that allow them to live well on land, including the ability to breathe through their skin and the lining of
their mouth and throat. They absorb oxygen through blood vessels just below their wet skin. They inhabit shallow
tidal flats and mangrove swamps. They dig deep burrows in soft sediments in order to thermoregulate, to avoid
marine predators during the high tide when the fish and burrow are submerged, and for laying their eggs. They hop
along on their large pectoral fins, and can travel faster on land that a man can walk!

Station 5. Fish Oddities
DEEPEST OF THE DEEP
In the abyss, the only light comes from fish that glow.
Some deep sea fish are bioluminescent. Like fireflies,
they create chemicals that glow when they mix. Some
of these fish have special pockets in their bodies
where they carry bioluminescent bacteria. The fish
look as if they are glowing, but really it’s the bacteria.
In other bioluminescent fish, they contain specialized
mitochondrial cells called photocytes. Some glowing
fish use their light to catch prey. !
The underside of the cookie cutter
shark is bioluminescent, glowing a pale
blue-green that matches the background
light from the ocean's surface. This
serves to camouflage it from creatures
beneath it. However, a small non
-luminescent patch appears black,
deceiving the shark's prey, smaller
predatory fish (like tuna), into thinking
the shark is an even smaller fish. When
the predatory fish tries to strike at the
shark, the shark strikes back, scoring
itself another meal.
This angler fish dangles its lighted
lure like bait on a fishing line. Curious
creatures that come too close end up
as the glowing fish’s dinner.

Station 5. Fish Oddities
DEEPEST OF THE DEEP
Chiasmodon
Food is so rare at the lower levels of the
sea that when it does come along it
must be taken advantage of. The
chiasmodon will swallow victims larger
than it is. To do this it must move its
heart out of the way and turn its gills
inside out. It gets its oversized meals
down with the help of movable teeth in
its throat. Its stomach stretches to hold
victim twice its own size.
Bristlemouths are well camouflaged. When
deep sea animals look up toward the ocean's
surface, they see other animals overhead as
dark shapes against a lighter background. But by
lighting two rows of photophores on its
underside, this deep sea fish avoids casting its
shadow on predators below––and can virtually
disappear.

Station