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Fishes
Kingdom - Animalia
Phylum - Chordata
Subphylum - Vertebrata
• Vertebrates:
• Include fish, amphibians, reptiles, birds, & mammals
• Have a notochord (slim, flexible rod) present in early stages that
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may be replaced by backbone in adults
Contain a dorsal, hollow bundle of nerves called the nerve or spinal
cord
Respire through pharyngeal or gill pouches during early
development
Have post-anal tail in early stages
Endoskeleton made of bone &/or cartilage
Anterior head with well developed brain & sensory organs
(Cephalization)
Closed circulatory system
Taxonomy of Vertebrates:
• Agnatha include hagfish & lamprey with long, eel-like
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bodies without jaws or paired fins & cartilage
skeletons
Chondrichthyes include sharks, rays, & skates with
cartilage skeletons, paired fins, & jaws
Osteichthyes are bony fish with jaws, paired fins, &
bone and cartilage in their skeletons
Amphibia include frogs, toads, & salamanders that go
through an aquatic larval or tadpole stage
Reptilia include snakes, turtles, lizards, & alligators that
live on land, are covered with scales, & lay a tough,
protective amniote egg
Aves are birds covered with feathers, adapted for
flying, & with hollow bones
Mammalia have hair or fur & females have
mammary or milk-producing glands
Evolution:
• Fossil record shows jawless fish without paired
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fins appeared first about 550 million years ago
Ostracoderm was a jawless, bottom-feeding
ancestor to the agnathans (modern jawless fish)
Development of jaws & paired fins allowed
better movement & increased ability to capture
prey
Extinct acanthodians or spiny fish were first
jawed fish with paired fins
Jaws probably developed from gill arches
(bone that supports the pharynx)
Ostracoderm
Acanthodian
Characteristics of Fish:
• Streamlined body & muscular tail for swimming
• Most with paired fins for maneuvering
• Body covered with protective scales & mucus layer to
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reduce friction when swimming
Have less dense body tissues & store less dense
lipids to help them float
Respire through gills
Most have a lateral line system or a row of sensory
structures running down each side of the organism to
detect changes in water temperature, pressure, current,
etc.
Most with well-developed sense of sight & smell
Some can detect electrical currents
Ectotherms (adjust body temperature to environment)
Two chambered heart (upper atrium receives blood
& lower ventricle pumps blood)
Agnatha (Jawless Fish):
• Hagfish (live in oceans) & lampreys (found in marine &
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freshwater)
Circular mouths
Sharp teeth & strong rasp-like tongue to tear hole in prey &
suck out blood & body fluids
Known as cyclostomes
Eel-shaped body
Mucus covers body
Skeleton made of cartilage
No paired fins
Gills without bony cover (called operculum)
Retain their notochord throughout their life
Hagfish are bottom dwellers in cold marine waters that burrow
in mud, scavenge on dead & dying fish, & have tentacles around
their mouth
Lampreys are usually parasites with a keen sense of smell to
locate prey, lay their eggs in freshwater streams, & are covered with
a poisonous slime
Chondrichthyes
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Includes sharks, rays, & skates
Endoskeleton of cartilage
Hinged jaws & paired fins
Placoid scales & tooth-like dermal spines on
scales
Marine
Carnivorous
Sharks are torpedo shaped
Rays & skates have broad, flat bodies with
wing-like fins and a tail
Placoid scales & tooth-like
dermal spines on scales
Shark Characteristics:
• Fast swimmers
• Large, oily liver (20% of body weight) makes them
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buoyant
Tough, leathery skin
Fierce predators
Whale shark is largest & filter feeds on plankton
Ventral mouth with 6-20 rows of sharp, replaceable
teeth
Short, straight intestine with spiral valve to slow food
movement
5-7 pairs of gills for gas exchange
Kidneys remove wastes & maintain water balance
Electroreceptors on head help find prey & navigate
Lateral line along side of body contains sensory cells to
detect vibrations & pressure
Separate sexes with external fertilization
Ray & Skate Characteristics:
• Usually harmless to humans
• Broad, wing-like pectoral fins used to glide
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through water
Flattened bodies with ventral mouth
Both eyes on top of head
Have protective coloration (darker on top &
lighter on bottom)
Feed on fish & invertebrates
Stingray with poison spine by tip of tail
Electric ray gives off strong, electric shock
Manta ray is largest
Manta Ray
Traits of Bony Fish
(Osteichthyes)
• Skeleton made of bone
• Hinged jaws
• Paired fins
• Gills for gas exchange
• Lateral line
• Body covered with scales & mucus
coating
• Includes lobe-finned, ray-finned, and
lung fish
Lobe-finned Fish:
• Muscular, paddle-like fins supported
by bone
• Gills
• Known as coelacanths
• Thought to be extinct until 1938 when
species found in Africa
• Live in deep oceans
Coelacanths
Lungfish:
• Use lungs & gills
• Eel-shaped body
• Live in shallow, tropical rivers of Africa,
Australia, & South America
• Come to surface & gulp air when oxygen
level is low
• Form mud cocoon & become dormant
if stream dries up
Lungfish
Ray-finned Fish:
• Fan-like fins supported by rays
• Includes salmon, perch, catfish, tuna, etc.
• Body covered with round, overlapping cycloid or
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ctenoid scales & mucus
Four sets of gills covered by bony operculum
Have movable fins
Dorsal fin(s) located on top keep fish upright & used
for defense
Caudal fin or tail moves side to side to help steer
Pectoral fins (paired) on each side behind the
operculum
Pelvic fins (paired) on ventral surface near the head
Anal fin (single) behind anus
Ray-finned Fish cont…
• Swim bladder is thin-walled sac in abdomen that
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creates buoyancy from diffusion of dissolved gas from
blood
Kidneys filter the blood & help maintain water balance
Ectothermic - body temperature regulated by the
environment
Keen sense of smell (nostrils) & have chemical
receptors over the body
Can detect the earth's magnetic field as a guide to
navigate oceans
Have separate sexes with external fertilization
Eggs hatch into fry
Salmon Life Cycle:
• Migrate up to 3200 kilometers following magnetic
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cues in the ocean
Follow mucus trails when navigating rivers
Return to birthplace to spawn
Males change color & jaw lengthens & develops a
hook
Female uses her tail to build gravel nest & lays up to
10,000 eggs
Male deposits sperm over eggs
Adults usually die after spawning
Pacific salmon return to sea when 15 cm long; while
Atlantic salmon may stay in river up to 7 years
Secrete mucus coating in river as return to sea
May stay in ocean 6 months to 5 years
• Anadromous fishes spend most of their
lives in the ocean but migrate to fresh
water to spawn. Salmon, smelt, shad,
striped bass, and sturgeon are common
examples
• Catadromous fishes live in fresh water but
migrate to the ocean to breed. Most of the
eels are catadromous.
Forms of Reproduction
• Oviparous animals are animals that lay
eggs, with little or no other embryonic
development within the mother.
• Ovoviviparity, ovovivipary, or
ovivipary, is a mode of reproduction in
animals in which embryos develop inside
eggs that are retained within the mother's
body until they are ready to hatch.
• Vivipary has two different meanings. In
animals, it means development of the
embryo inside the body of the mother,
eventually leading to live birth (as
opposed to laying eggs).