Chapter 30 Fishes and Amphibians

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Chapter 30 Fishes and Amphibians

• 30.1 Fishes
• 30.2 Amphibians

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Fish have all the characteristics of a chordate

• Notochord
• gill slits
• muscle blocks
• hollow dorsal nerve cord
• bilateral symmetry
• Endoskeleton

• Coelomate
• Closed circulatory systems
• Complex brains
• Sense organs
• Efficient respiratory

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3 Classes of Fish

• Agnatha jawless fish, lampreys and hagfish
• Chondrichthyes cartilaginous fish, rays, and
  sharks
• Osteichthyes bony fish

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Fish

• More than 200,000 species of fish. Mort being
  discovered all the time
• 95 are Osteichthyes
• Inhabit nearly every aquatic environment on the
  planet

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Fish use gills to breathe

• Gills are made up of feathery filaments that
  contain tiny blood vessels.
• Water goes in the mouth over the gills and then
  out through slits on the side of the fish
• Oxygen and Carbon Dioxide are exchanged through
  the capillaries

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Circulation in fish

• 2 chambered heart
• Closed circulatory system
• Blood flow is relatively slow because most of the
  pump action is used to get blood through the gills

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Sexual reproduction

• All fish have separate sexes
• Most have external fertilization
• Produce large numbers of eggs at one time
• Some cartilaginous fish (such as sharks) have
  internal fertilization and few eggs at a time
• Reproduction in fish is often called spawning
• Most do not care for offspring after spawning
• Some fish have internal fertilization and live
  birth (live bearers)
• Live bearers MAY care for young for a short time

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Fins

• Fan shaped membranes used for steering, swimming
  and balance
• Most have paired fins
• Attached to and supported by the endoskeleton
• Paired fins evolved into limbs in other animals
  and wings for birds

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Sensory Systems

• All fish have highly developed sensory systems
• Lateral line system in bony fish, a series of
  fluid filled canals running along their sides
  that let it sense movement and vibration in the
  water
• Some (like sharks) also have acute senses of smell

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Scales

• Hard bony plates formed from the skin
• Can be toothlike, diamindshaped, coneshaped or
  round.
• Some fish (like catfish ) dont have scales
• Shark scales are like the teeth of other species
• Can use the annual growth rings in the scales to
  tell age in some species

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Jaws

• One of the most important traits vertebrates
  evolved
• Jaws let animals grasp and crush prey

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95 of fish have skeletons of bone

• Bone hard, mineralized living tissue
• Makes up the endoskeleton
• Bone allowed fish to adapt to lots of habitats
  and eventually to living on land
• separate vertebrae allow for flexibility

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Swim Bladder

• A thin walled internal sac found just below the
  backbone in bony fish
• Can be filled with oxygen and nitrogen gas that
  diffuses out of the blood
• Allows fish to adjust their buoyancy (lets them
  rise or sink in the water) by putting more gas in
  or letting it out

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Diversity of fish
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Agnathans jawless fish

• Lampreys and hagfish
• No jaws but are heavy feeders
• They have teeth
• Hagfish attach themselves and drill a hole in
  their prey with their teeth and suck out the
  insides
• Skeletons are made of cartilage

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Cartilaginous fish

• Sharks, rays and skates
• Skeletons made entirely of cartilage
• Sharks are considered living fossils having
  changed little in hundreds of thousands of years.
• All are predators
• Some have poison glands or may generate
  electricity for defense or feeding

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3 sub-classes of bony fish

• Lungfishes - Have both gills and lungs
• Lobe-finned fishes - only one living species
  (coelacanth) fins are fleshy and used to walk
  along the seafloor. Are the ancestor of all
  tetrapod (4 legged) animals
• Ray finned fish fins are fan shaped membranes
  supported by spines called rays. Catfish, tuna,
  salmon

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Origins of Fish

• Evolved during the Ordovician period more than
  500 million years ago
• jawless fish were the 1st fishes
• Ostracoderms were heavy armored, jawless fish
  with cartiliginous skeletons but bony shields
  over their heads and necks
• From these evolved the bony fish of today some
  time during the Devonian period
• bony fish evolved during the Devonian period (400
  million years ago)

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30.2 Amphibians

• Amphibia means double life
• Includes 3 orders
• Caudata ( salamanders and Newts)
• Anura (frogs and toads
• Apoda ( legless caeecians

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Characteristics

• Thin, moist skin
• 4 legs (except for the apoda)
• No claws on their toes
• Most live on land as adults
• Require water for reproduction
• Fertilization is usually external
• Water is needed to transport sperm so eggs are
  usually laid in water
• No protective membranes or shells on their eggs

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Amphibians are ectotherms

• Ectotherms (cold-blooded) are the same
  temperature as the surrounding air or water
• Must live in places that are warm all year round
  or must hibernate when its too cold
• May also enter a state of estivation (like
  hibernation) if it gets too hot

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Metamorphosis

• Eggs hatch into tadpoles (aquatic stage)
• Tadpoles have gills, fins, tails and a 2
  chambered heart JUST LIKE FISH
• Then change and develop into their adult form
  over time
• Adults have lungs, legs and a 3 chambered heart
• Salamander young look like the adults but have
  gills not lungs. Some species dont get lungs
  and breathe through their skin

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Walking and Oxygen

• Walking requires lots of energy
• Need more food and oxygen to move muscles to walk
• The 3 chambered heart allows for enough oxygen to
  get to the cells
• There is some mixing of oxygen rich and oxygen
  poor blood in the 3rd chamber

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Amphibian skin

• Must remain moist so they can exchange gasses
  through it
• Toads have thicker skin and may live mainly on
  land, but must return to water to reproduce

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Diversity of Amphibians
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Anura frogs and toads

• No tails
• Breathe through lungs
• Frogs - long hind legs and smooth moist skin
• Toads bumpy dry skin and short legs
• All eat insects
• Many secrete chemicals through their skin for
  defense
• Have vocal cords and produce loud mating calls
• Spend part of their lives in the water and part
  on land but must return to water to reproduce

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Caudata - Salamanders

• Long slender body
• Look like lizards but have smooth moist skin and
  no claws
• Some are completely aquatic, others live in damp
  places on land
• Range in size from a few centimeters to 5 feet
• Young look like adults
• All are carnivorous

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Caecilians

• Limbless amphibians
• Short or no tail
• Mainly tropical
• Small eyes often blind
• Eat earthworms and other invertebrates found in
  soil

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Origins of Amphibians

• Evolves some 350 million years ago as a tetrapod
  fish began to come onto land
• Earliest ones had both lungs and gills and likely
  could move over mud to get to another water
  source (a serious advantage)

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Life on Land

• Life on land was very advantageous for early
  amphibians - no predators lots of food and
  shelter
• but air temperatures vary greatly and they had
  to remain where it was warm or evolve hibernation
  and estivation abilities
• Early land movement was probably clumsy and slow