Fishes and Amphibians

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Fishes and Amphibians

• Chapter 26-2

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Characteristics of Fish

• Phylum Chordata (have a spinal cord)
• Have a notochord(flexible supporting rod that
  runs along the dorsal surface of the body),
  hollow dorsal nerve cord,(on the back side of the
  body that conducts impulses) and pharyngeal
  slits(structure that appears in pairs in throat
  region)
• The notochord is replaced by a backbone
  (vertebral column)

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Definition of a fish

• Aquatic vertebrates
• Scales
• Fins
• Pharyngeal slits
• Some excpetions (some fish do not have scales)

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Groups of fish

• Jawless (Agnaths)
• Bony (Class Osteichthyes)
• Cartilaginous (Chondrichthyes)- over 97 of all
  living fish today belong to this class

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How did fish evolve?

• They are the first vertebrates to evolve.
• First fish were jawless, body covered with bony
  plates (540 mya)
• Major adaptive radiation occurred
• Jawless with little armor (extinct)
• Armored but in a new form
• Some had jaws that advanced them in feeding

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More about evolution

• Jawless fish are limited to filter feeding
• Jaws can crush, nibble, and be used in defense
• Fish also evolved the paired pectoral fins and
  pelvic fins which gave them better control of
  movement in water.
• The fins later evolved into limbs and shoulder
  bones of terrestrial vertebrates

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Fish Anatomy

• Fish have evolved many adaptations to many
  environments
• Feeding every form of feeding
• Sawfish kill and stun prey
• Parrotfish have teeth fused into a beak to bite
  coral
• Archerfish spits drops of water and shoots down
  insects
• Most fish swallow the prey whole

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Digestion

• Mouth?Esophagus?Stomach (partially broken down)
• Pyloric ceca(little pouches that break down food)
  
• Intestines (complete digestion and absorbtion)

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Respiration

• Most use gills that are located on either side of
  the pharynx (connects mouth to digestive tract)
• Many capillaries to increase surface area for gas
  exchange
• Water enters the mouth?over the gill
  filaments?slits in the sides of the pharynx
• Some use the swim bladder (organ used to control
  the depth of swimming) as lungs (ex. Siamese
  fighting fish)

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Internal Transport

• Closed Circulatory System
• Heart has 2 chambers
• O2 poor blood collects in the atrium
• Then pumps into the ventricle
• Blood is pumped through the aorta to the gills
• Then blood is transported to the rest of the body
• Collects in Sinus Venosus (veins) then re-enters
  the atrium

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Excretion

• Nitrogenous waste in the form of NH4
• Through gills in the water
• Kidneys filter blood
• Also control the amount of water in the body
  (salt-water fish need to keep water and
  fresh-water fish need to get rid of excess water)

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Response

• Fish have a well-developed nervous system
• Olfactory bulbs and Cerebrum at front of head-
  smell (chemoreceptors)
• Optic lobes- sight
• Cerebellum-movement
• Medulla-internal organs and balance
• Lateral- line detect motion

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Internal Anatomy
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Reproduction

• Separate sexes- male and female
• Oviparous-lay eggs
• Ovoviviparous-eggs develop within female
• Viviparous- true live-bearing

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Jawless Fish

• No backbones, just notochord
• Lampreys- parasitic, large sucking disc at the
  head to latch on to prey
• Hagfishes-pinkish-grey wormlike bodies
• No eyes, feed on dead or dying fish
• Secrete a lot of slime, have 6 hearts, and
  sometimes tie themselves in a knot!

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Hagfish
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Lamprey
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Sharks and Relatives

• Endoskeleton made out of cartilage
• Tough scales
• 3,000 teeth
• Filter feeders, eat crustaceans,mollusks
• More people are killed by lightning than sharks

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Sharks and Rays
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Bony Fish

• 15,000-40,000 species alive today
• Ray-finned-(thin bony spines that are connected
  by a thin layer of skin to form fins.)
• There are many adaptations of fins ( poison,
  leaping, climbing)
• Only 7 are not classified as ray-finned fish

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Lungfish

• Some can use gills to eliminate CO2 and gulp air
  to receive O2
• Coelacanth is a lobe-finned fish
• Few bones in fin bases
• Probably used these in ancient times to move from
  pool to pool
• We thought they were extinct(found in 1938)
• Closest living relative to land vertebrates

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Coelacanth
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How do fish fit into the world?

• Important food source in many ecosystems
• Control population growth (especially some
  plants)
• Recreation in tanks

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Amphibians

• Smallest groups of vertebrates
• Fishlike aquatic organisms that breathe through
  gills, where as the adults are terrestrial and
  breathe through skin (there are exceptions)
• Aquatic larvae
• Eggs do not have a shell
• Skin has not protection
• If skin dries out they suffocate

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Evolution

• 360mya
• From lobe-finned fish
• Bones became stronger for movement on land
• Scales
• Ears
• Eyelids

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Why were amphibians so successful?

• The land was empty of life
• Well established plant life
• Arthropods were there (includes insects)
• Plenty of food and space
• Many became extinct after climate changes

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Form and function of Amphibians

• Feeding
• Larvae filter feed
• Tadpoles are herbivorous
• Adults are carnivorous
• Food enters Mouth?Esophagus?Stomach?Small
  intestines(food absorbed)?Large intestine
  (absorbs water)? Cloaca (gets rid of waste)

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Internal Anatomy of Frog
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Permian Period
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Respiration

• Lungs, Mouth, Skin
• Skin is thin and and rich in blood vessels
• They cannot exhale and inhale like we do.
• Fill mouth with air and force it into lungs
• Frogs croak by forcing air into a pair of vocal
  sacs in the back of the mouth

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Internal Transport

• Linked to lungs in adults
• Double loop
• 1st loop carried O2 poor blood from heart to
  lungs and takes O2 rich blood from the heart to
  the rest of the body
• 2nd loop takes O2 rich blood from the heart to
  the rest of the body and and O2 poor blood from
  the body back to the heart

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The heart

• Has 3 chambers Left atrium, right atrium and
  ventricle
• Blood from the body enters in the vena cava?
  sinus venosus? right atrium
• Blood from the lungs enters the left atrium
• Atria contract?empty into ventricle?bulbus
  cordus?aortic arches to the rest of the body

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Heart
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Excretion

• Use kidneys to filter Nitrogenous waste from
  blood
• Urine travels through tubes called ureters into
  the cloaca
• Stored in bladder or expelled

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Response

• Well developed nervous system
• Eyes can move around and are protected by a
  transparent nictitating membrane
• Can hear and sounds are used in calls for mating
• Do not regulate body-temp
• They can hide, run away, produce poison, or use
  camouflage to escape predators

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Reproduction

• Male climbs on back of female
• She releases eggs in the water
• Male fertilizes these
• Surrounded by a thick jelly as they develop
• Tadpoles develop in 1-3 weeks
• Not all amphibian eggs are fertilized externally

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Frog Life Cycle
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Salamanders

• Keep tails as adults
• Larvae and adult are carnivores
• Some have gills for water
• Some switch and live on land and return to the
  water to breed

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Eastern Redback Salamander
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Frogs and Toads

• Most live in water
• Some toads have inhabited dry land (they can
  burrow in soil and absorb water like plants)
• Many produce toxins

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Poison frogs
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How do Amphibians fit into the world?

• Prey on insects
• Tadpoles eat a lot of algae
• Researchers are using poisons to see how the
  nervous system works
• Salamander can regenerate and frogs cannot- under
  research