CHAPTER 32
I.
History and diversity of fishes
A. Jawless fishes were the first vertebrates
1. Introduction
a) Starts over 500 million years ago
- Cambrian period
b) First animals with backbones
c) Class Agnatha
- name means “not jaw”
- breathed with gills
- no fins
- developed primitive fins by the end of the Ordovician
- Also developed massive shields of bone
d) Ostracderm (order)
- armored fishes
- Ostrakon means “shell”, dermis means “skin”
- At one time there were 5 orders with 40 families
- Most extinct by the end of the Devonian period
- Descendants are lampreys and hagfishes, only
remaining Agnathans
2. The evolution of Jaws
a) Development of jaws
- key evolutionary advancement
- occurred 440 million years ago
- gill arches: jaws
- teeth developed from skin that lined the mouth
b) Class Acanthodia
- spiny fishes
- first to develop jaws
- common in the early Devonian period
- extinct by the end of the Devonian
- internal skeletons made of cartilage with some bone
(foreshadows larger role that bone would play)
c) Placoderm
- mid-Devonian
- stronger, more efficient jaws
B. The rise of sharks and bony fishes
1. Introduction
a) End of Devonian almost all early fishes were replaced by
sharks and bony fishes
b) Sharks and bony fishes evolved about 400 million years
ago
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c) Jaw was improved
- the next pair of arches was transformed into a
supporting strut (prop) called a hyomandibular
- joined the rear of the lower jaw to the rear of the skull
- enables the mouths to open very wide
e) Replaced primitive fishes because of their superior design for
swimming
- streamlined bodies, well adapted for rapid movement
through the water
- head acts as a wedge
- body tapers back to the tail, allowing the shark to slip
through with minimal resistance
- assortment of movable fins
2. Sharks became top predators
a) In carboniferous period sharks became dominant
vertebrates
b) Class Chondrichthyes
- Cartilaginous fishes
- Skeleton made completely of cartilage
c) Many died out during the Permian period
- those who survived underwent evolution
d) Today they are the major predators in the seas
e) Shark skeleton
- cartilage
- calcified
: strengthened by the mineral calcium carbonate
: deposited in the outer layers of cartilage
- light, strong skeleton
f) Shark mouth
- bony teeth
- arranged in 6 to 10 rows
- front teeth pointed and sharp for biting and cutting
- back rows are immature teeth
- when a functional tooth moves forward
- guarantees the teeth are always new and sharp
g) Reproduction
- eggs are fertilized internally
- male grasps the female with modified pelvic fins
called claspers
- sperm runs from the male into the female through
grooves in the claspers
- some shark species lay eggs
- other species have live births: offspring called pups
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3. Bony fishes dominate the waters
a) Members of the class Osteichthyes
b) Evolved about 400 million years ago
c) Evolved a heavy internal skeleton made of bone
- very strong
- provides a solid base for muscles
d) Evolved in freshwater
- first bony fishes had paired air sacs
: filled with gas to make the fish more buoyant
e) Ray-finned bony fishes
- swim bladder: replaced air sacs
- amount of air can be adjusted to adjust depth in water
- unlike sharks that do not have a swim bladder: swim
or sink
f) Teleosts
- most advanced of the ray-finned bony fishes
- highly mobile fins
- very thin scales
- completely symmetrical tails
- evolved during the Jurassic period
: forms were similar to sardines, tarpons and eels
- second evolution in mid-Cretaceous period
: produced fishes with heavily muscled bodies and a
second dorsal fin
: salmon, trout, carp, cod, haddock
- Third evolution in early Tertiary period
: highly specialized fishes with more flattened bodies
: perches, sunfishes, bass, snappers, flounder,
barracudas, swordfish
C. Lobe-finned fishes paved the way to land
1. Lobe-finned fishes evolved 390 million years ago
a) Seven species survive today
b) Six of the species are called lungfish
c) The seventh species is the Coelacanth
2. Structure
a) Each fin consists of a long, fleshy, muscular lobe
- supported by a central core of bones
b) Muscles within each lobe can move the fin rays
independently of each other
3. Evolutionary role
a) Amphibians evolved from lobe-finned fishes
b) Lungfish are still found in Australia, South America, and
Africa
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II.
Key adaptations of fishes
A. Introduction
1. Great diversity
2. Ocean or freshwater
3. Vary in size
4. Arctic to tropics
B. Characteristics of Fishes
1. Gills
a) Fine filaments of tissue
b) Located in the back of the mouth
c) Pump water through their mouths that passes over the gills
and exits the body through slits in the side of the side of the
throat
d) Obtain oxygen required for metabolism from the water
2. Vertebral column (backbone)
a) Surrounds the spinal cord
b) Brain encased within a protective covering called the skull
or cranium
3. Single-loop blood circulation
a) Blood pumped from the heart to the gills
b) The blood is oxygenated at the gills
c) From the gills the blood passes to the rest of the body then
returns to the heart
4. Nutritional requirements
a) Unable to synthesize aromatic amino acids (cannot
breakdown ring-structured amino acids)
b) Must consume these amino acids in their diet
C. Bony fishes have additional adaptations
1. Swim bladder
a) Able to secrete and absorb its own gases
b) Cells that make up the swim bladder generate carbon
dioxide
- fills the bladder with carbon dioxide gas
c) Filled swim bladder makes the fish rise
d) Carbon dioxide is absorbed into the fish’s bloodstream
- causes the fish to sink
e) Different than primitive bony fish that had to gulp air to fill
their swim bladder
2. Lateral line system
a) Specialized sensory system
b) Extends along each side of the fish’s body
c) Nerve impulses from ciliated sensory cells permit the fish
to perceive its rate of movement
- trout use it to obtain the sensory information it needs
to orient itself with its head upstream
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d) Also enables a fish to detect a motionless object by the
movement of water reflected off the object
- equivalent to hearing
e) The sound receptors within the ears of terrestrial
vertebrates are thought to have evolved from lateral line
receptors
3. Gill covers
a) Operculum: hard plate that covers the gills
b) Movements of the opercula help a bony fish to pump water
over the gills
- enables the fish to breathe
c) Allows bony fishes to move water over their gills while
remaining stationary
d) Enables a bony fish to conserve energy
e) Other fish without opercula usually have to move forward
to pass water over the gills
D. Yellow perch
1. External structures
a) Lateral line
- sense organ
- detects vibrational disturbances
- information is used to direct movement, detect objects
including predators and prey
b) Fins
- caudal fin: propels the fish forward
- dorsal fin: prevent the perch from rolling
- ventral anal fin: keeps the fish from slipping sideways
- paired pectoral and pelvic fins: assist the fish in going
up and down through the water, in turning sharply left
or right, and in stopping quickly
c) Opercula
- a hard flap that covers the gills with an opening at the
rear
- movements of the opercula draw water into the mouth
d) Scales
- thin, bony disks
- grow from cavities in the skin
- grow throughout the life of the fish
- grow more rapidly in spring than winter so the scale
forms growth rings
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2. Internal structures
a) Reproductive organs
- produce gametes (sperm and egg)
- eggs are fertilized externally
- male deposits milt, a fluid containing the sperm, on
strings of eggs laid by the female
b) Brain
- divided into anterior, middle, and posterior regions
- optic lobes: receive sensory information from the eyes
- olfactory bulbs: devoted to receiving information
concerning smell from chemical-sensing cells
- cerebrum: processes mainly sensory information
- cerebellum: coordinates muscle activity
- medulla oblongata: controls the function of many
internal organs
c) Digestive system
- food enters the mouth, passes from the esophagus to
the stomach, where digestion begins
- liver and pancreas secrete digestive chemicals into a
short intestine, where these substances help break
down the food
- absorption of digested food occurs through the inner
lining of the intestine
- undigested food exits through the anus
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