Fish and Amphibians
Chapter 30 TURBOBLAST Edition!
What is a fish??
• All fish are:
– Chordates, vertebrates, bilaterally symmetrical
coelomates
– Have endoskeleton, closed circulatory systems,
nervous systems with complex brains & sense
organs, efficient respiratory systems
• Ichthyology: the study of fish (Gr: icthyes = fish)
Four classes of Fish
Agnatha “without jaws” (Gr: gnatho = jaw)
Myxini
• 2 classses: Cephalaspidomorphi
lampreys
hagfish
Chondrichthyes “cartilage fish”
Chimaera
sharks
Osteicthyes “bony fish”
skates & rays
Fishes breath using gills
Fish takes in water
through its mouth,
water passes over
gills and out side slits
Oxygen & carbon dioxide
are exchanged through
capillaries in gill
filaments
Fish have hearts, too!
• All fishes have two-chambered heart
– One chamber receives deoxygenated blood, the
second chamber pumps blood directly to gills
• Blood takes up oxygen in gills, pumped around the
body, then back to the heart
*This circulation
allows fish to
efficiently make ATP
through cellular
respiration!
Sexual reproduction
• External fertilization in most fishes
– Simultaneous release of gametes into water
– Sometimes deposited in protected areas
(plants, rocks, etc.)
– Most fishes produce large #s of eggs at once,
some produce small # of larger eggs
• Cartilaginous fish have internal fertilization
– Skates deposit fertilized eggs on ocean floor
– Some sharks & rays carry developing young
inside bodies
• Spawning – bony fish (external fertilization &
development), produce millions of eggs, provide
little to no care for young, only a few survive until
adulthood (ex. Salmon, cod) https://www.youtube.com/watch?v=Jgp6OjpfrQo
– Some adults protect young fry when threatened by
danger (Ex. Gouramis, cichlids, tilapia
http://youtu.be/QkmmpSrbbjM
Pairs of fins & Movement
• Fish in Chondrichthyes and Osteichthyes have paired fins
– Fins are fan-shaped membranes used for balance, swimming,
steering
• Lobe-finned vs. Ray-finned fishes
– Lobe-finned fish have sturdy bone structure and stronger pectoral muscles,
foreshadow the evolutionary development of all tetrapods on land
• Ray-finned fish have webbed spines,
comprise 99% of all fish species
Sensory systems in fish
• Lateral line system
– Enables fish to sense objects and changes in their
environment
• System of fluid-filled canals running along sides of fish,
detect vibrations & movement in the water
• Complex eyes
– Can see objects and contrast in water
• Vision varies greatly among fishes (some in darker waters
have reduced, almost nonfunctional eyes
• Sense of smell
– Can detect extremely small amounts
of chemicals in water, helps locate prey
Most Fish Have Scales
• Cartilaginous & bony fishes have skin covered
by overlapping scales (like roofing tiles)
– Can be classified by the types of scales
– Scales are thin bony plates formed from the skin
Evolution of the Jaw
• Jaws evolved in fishes
– Have the advantage of grasping & crushing prey
– Fish with jaws could feed on greater variety of food
• Sharks have up to 20 rows of razor-sharp teeth,
pointing back into their mouth (stops prey from
escaping)
Bony, flexible skeletons
• Osteichthyes are most
successful fish group
– Skeletons are mineralized
(w/ calcium) & rigid
– Development of bone
allowed fish to adapt to
variety of aquatic
environments, and
eventually to land
• Bony fishes have separate
vertebrae for flexibility
Swim Bladders
• Swim bladder is a thin-walled internal sac that
fish can contract to change gas/liquid
concentration
• Squeeze  higher
pressure, gas dissolves
into liquid, fish can
descend deeper
• Relax  lower pressure,
gas accumulates into
bubbles, fish can rise
toward water surface
Fish Diversity
• Hagfish & Lampreys are jawless, and feed with a
rasping, suckerlike mouth
http://youtu.be/tKTRv3hx1s0 http://youtu.be/-SYhOD1Yx10
– Skeletons are made of flexible cartilage
– Hagfish create thick slime to avoid predators, tie into knots
to slip out of tight spots while feeding http://youtu.be/pmaal7Hf0WA
http://youtu.be/5kS64P-o5mU
• Sharks, skates and rays are cartilaginous fishes
– Similar to 100,000 year old fossils, considered “living fossils”
– Sharks are most well-known predators of the oceans http://youtu.be/iLHTtDbtDFA
– Rays & skates have flat bodies, feed near ocean floor http://youtu.be/9D06j__CZHs
• Lobe-finned fishes – 6 species (ex. lungfish, coelacanth)
• Ray-finned fishes - ~30,000 species (ex. catfish, perch,
salmon, cod)
http://youtu.be/cIgHEhziUxU
Origins of Fish
• Fossils from the Cambrian Period 500 mya show the existence of
fishes
– Ostracoderms (early jawless fish) were dominant vertebrates
• Possessed a cartilage skeleton and bony head plate
• Most were extinct by the end of Devonian Period 354 mya
• Present-day agnathans appear to be direct descendants
• Ostracoderms swam sluggishly (weighed down by heavy, bony
external armor)
• Development of calcified bone in early vertebrates was
important for muscle attachment, improved locomotion
• Jawless ostracoderms are considered common ancestors of all
fishes (and subsequent tetrapods)
• Lobe-finned fishes appeared 395 mya (ex. Coelacanth
http://youtu.be/NzzxOlFJtzg,
lungfish http://i306.photobucket.com/albums/nn263/headbanger_jib/protopterus%20annectens/DSC_7437.jpg
Amphibians
• What is an amphibian?
– Gr: Amphi = “both,” bio = life  “double life”
– Transition from aquatic larvae to air-breathing, semiterrestrial adult is unique in amphibians
• 3 orders in class Amphibia:
– Caudata (salamanders & newts)
– Apoda (caecilians)
– Anura (frogs & toads)
• All have moist skin, most have 4 legs, capable of
terrestrial existence, rely on water for reproduction
Rely on external temperature
• Amphibians are ectotherms, whose body
temps depend on external sources
– Usually found in warmer habitats
– Become dormant when temperature ranges
become too cold or too hot
• Often bury themselves & wait out the harsh season
Metamorphosis
• Fertilized egg  tadpoles (aquatic stage of most amphibians)
Tadpoles have fins, gills, 2chambered heart like fish
Can avoid competition with
adults by occupying a
completely separate niche
Eventually develop legs, lungs,
and a 3-chambered heart
(needed for life on land)
• Young salamanders
resemble adults but have
gills and tail fins as larvae,
while adults breathe only
through skin
• Most salamanders have 4
legs, but some have just 2
front legs
Walking takes energy!
• Early amphibians required lots of food
and oxygen to get around on land (they
were uncoordinated on land)
• 3-chambered heart enabled oxygenrich blood to reach body tissues more
efficiently
– Some mixing of oxygen-rich & oxygen-poor
blood happens, so as blood is pumped
near skin, more gas exchange occurs
across the moist skin
• Most amphibians are limited to
life on water’s edge or moist areas
– Toads live in drier areas but still
return to water to reproduce
Amphibian diversity
• Not always easily seen, but numerous worldwide
(Must complete part of life cycle in water)
• Frogs & Toads (Anura) http://youtu.be/Tz1vyIavi_M
• Salamanders & Newts (Caudata) http://youtu.be/jX3TGK1Ey9w
• Caecilians (Apoda)
http://youtu.be/DMvL4zOLSeM
What’s that sound?
• Acoustic communication is essential for the frog's
survival
– Territorial defense and in localization and attraction of
mates
• Frogs can hear above and below water
– Tympanic membrane (eardrum) size & distance apart
is related to frequency of calls
• The call or croak a frog makes is unique to its
species, some species do not vocalize
– Pass air through larynx (“voice box”) in throat, often
amplified inflated with vocal sacs
– Ex. Bullfrog http://youtu.be/M02_dnl9zCA, treefrog http://youtu.be/080Dv8pV2y8
wood frog http://youtu.be/BaTret-W7DA Spotted toad http://youtu.be/j5vGZsCP1Co
Amphibian origins
• 360 mya freshwater seas filled with carnivorous fishes
– Early tetrapods may have used limbs to move among
marshlands
– Later fossils show ability to lift body off the ground
– Ability to breathe air with lungs evolved
• Adaptations necessary to provide support to land-heavy bodies,
efficient respiration, membrane protection from dryer air (prevent
water loss)
• Challenges of life on land:
– More O2, large food supply, shelter, no predators
– But air changes temperature faster, bodies are clumsier on
land
• Some early amphibians had legs at right-angles to body
• Became dominant terrestrial predators during warm,
wet Carboniferous period 345 mya