FISHES

1
FISHES
2
Fishes

• Three traditional vertebrate classes that remain
  aquatic.
• All three classes well adapted to aquatic
  environment.

3
Fishes

• All fishes retain four (4) primitive characters
• Streamlined body
• Vertical tail fin
• Gills for gas exchange
• Lateral line system,
• No ears

4
Fishes

• Three traditional classes
• Class Bony Fishes
• Class Cartilaginous Fishes
• Class Jawless Fishes

5
Class Bony Fishes

• 30,000 species.
• Majority of living vertebrate species.
• Bony skeleton, well developed skull
• Fins supported by cartilage or bony rays and
  minute scales
• paired fins
• pectoral, pelvic
• median fins
• dorsal, anal, caudal

6
Bony Fishes

• Fins
• paired fins
• pectoral, pelvic
• median fins
• dorsal, anal, caudal

7
Bony Fishes

• Bony dermal scales
• covered by thin epidermis
• NOT homologous to reptilian scales.
• Operculum covers gills one gill slit each side.

8
Bony Fishes

• Lungs, often modified to swim bladder.
• Examples
• sturgeons
• gars
• catfish
• trout
• bass
• Northern pike
• American eel
• note paired fins, jaw, operculum

9
Class Cartilaginous Fishes

• 400 - 600 spp.
• Skeleton of cartilage, bone lost.
• Fossil placoderms and jawless fishes had bone
  tissue, prob. ancestral to both Cartilaginous
  Bony fishes.

10
Class Cartilaginous Fishes

• Cartilaginous skull poorly developed, esp. dorsal
  to brain
• Fins supported by cartilage or horn-like rays

11
Cartilaginous Fishes

• No ribs.
• No lungs or swim bladder.
• Separate gill slits, usually 5
• Placoid scales,
• tiny, tooth-like
• Enlarged at edge of mouth ? teeth
• Homologous to teeth in all other vertebrates.

12
Cartilaginous Fishes

• Sharks,
• Rays
• specialized flattened sharks

13
Development of Jaws

• All animals studied so far are Jawed
  Vertebrates
• Jaws developed from gill arch,
• Allowed diverse diet

14
Class Jawless Fishes

• Survivors of earliest vertebrates
• No jaws,
• can not close mouth
• No scales
• No paired fins, only median tail fin (continues
  dorsal ventral to anus)
• Single median nostril on top of head
• Circular gill slits
• 7 or 12 pairs on sides of pharynx.

15
Jawless Fishes

• Hagfishes
• tentacles around mouth
• predators on worms, mollusks
• scavengers
• 20 spp. in 4 genera
• Lampreys
• circular mouth, no tentacles
• filter feeders, or
• external parasites of bony fishes
• 30 spp. in 10 genera

16
Jawless Fishes

• Life cycle of sea lamprey
• Adult parasitic, feeding stage
• Adults swim into small freshwater streams to
  breed
• Larvae live in sediment as filter feeders up to
  seven years
• Metamorphosis, migration to lake or sea to become
  parasitic adults

17
Jawless Fishes

• Sea lamprey in the Great Lakes
• Lake Ontario since end of last Ice Age, prevented
  from entering upper lakes
• Welland canal
• Sea lamprey devastated commercial fishing
• Control

18
Overview of where we have been

• All animals studied to date belong to
• Phylum Chordata
• notochord
• dorsal nerve cord
• pharyngeal arches/clefts
• bear gills in fishes,
• modified to other structures in terrestrial
  animals
• postanal tail

19
Review

• Subphylum Vertebrata
• Notochord reduced, replaced by bony or
  cartilaginous vertebrae
• Some notochord tissue usually remains
• Pharyngeal arches bear gills
• or developed into other organs hyoid bone,
  larynx
• Liver
• Pancreas

20
Review

• Subphylum Vertebrata
• 7 traditional classes
• Jawless fishes
• Cartilaginous fishes
• Bony fishes
• Amphibians
• Reptiles
• Birds
• Mammals

21
Invertebrate Chordates

• Two more subphyla of Chordata, lack
  distinguishing characters of Vertebrates
• Subphylum Urochordata
• tunicates, sea squirts
• Subphylum Cephalochordata
• lancelets, amphioxus

22
Subphylum Urochordata
23
Subphylum Cephalochordata