BIO190: The Class: Fishes: Lesson 27

The Fishes

Fishes are the most ancient,the most diverse, and the most numerous of the Subphylum Vertebrata within the Phylum Chordata, constituting four of the eight vertebrate classes and one-half of the approximately 48,000 recognized vertebrate species.

NAU's Department of Biological Sciences offers a course in ichthyology. Contact the Biology Department's Advisement Center for details 520-523-9304.

Dr. Linn Montgomery, an NAU Biology Professor, studies fishes. If you want more info on his research interests, call him at 520-523-7505.

• respiration by gills

• ectothermic

• aquatic verts

• most have scales

• two-chambered heart
  1. atrium
  2. ventricle
  3. nucleated RBCs

The hagfishes are an entirely marine group that feeds on dead or dying fishes.

• hagfish

• marine

• no vertebrae (cranium present)

• feed mostly as scavengers

• non scaly skin with slime glands

• no paired appendages

• cartilaginous skeleton

• excretory system
  (kidneys)

• digestive system
  (no stomach)

• nervous system
  (dorsal nerve cord with brain; 10 pairs cranial nerves; no cerebellum)

• sensory
  1. taste
  2. smell
  3. degenerate eyes
  4. pair semicircular canals

• reproductive system (dioecious)

• external fert.

All the lampreys of the Northern Hemisphere belong to the family Petromyzontidae. Their name refers to the lamprey's habit of grasping a stone with its mouth to hold its position in a current.

• lampreys

• some marine/some FW

• some parasitic/some free living

• long eel-like body

• no scales on skin

• median fins

• no paired appendages

• cartilaginous skeleton

• tongue with teeth

• sucker shaped mouth

• 7 pairs gills/ each with ext. opening

• excretory system
  (kidneys)

• nervous system
  (dorsal nerve cord; brain; cerebellum present)

• digestive system
  (no stomach)

• sensory
  1. taste
  2. smell
  3. hearing
  4. eyes developed
  5. 2 pairs semicircular canals

• reproductive system
  (dioecious)

• external fertilization

There are about 850 living species in the class Chondrichtyes.

• mostly marine

• cartilaginous skeleton

• Subclass Elasmobranchii
  1. sharks, rays, skates
     Animal Bytes: Shark
     Shark Museum
     Fiona's Shark Mania
  2. heterocercal caudal fin
  3. paired pectoral/pelvic fins
     (males - modified pelvic fins = claspers)
  4. 2 dorsal fins
  5. ventral mouth
  6. placoid scales
  7. teeth = modified placoid scales
  8. digestive system
     1. stomach present
     2. spiral valve (intestine)
     3. liver/gall bladder/ pancreas; all present

  9. respiratory system
     (gills/spiracles/ no operculum)

  10. no swim bladder

  11. excretory system
      (kidneys)

  12. nervous system
      1. brain
      2. additional info. (pg. 505)

  13. sensory
      1. smell
      2. vibrations (lateral line)
      3. electroreception
      4. vision

  14. reproductive system
      1. dioecious
      2. cloaca

  15. fert ext.

The members of the small Subclass Holocephali, distinguished by such suggestive names as ratfish, rabbitfish, spookfish, and ghostfish, are remnants of a line that diverged from the earliest shark lineage which originated at least 350 million years ago.

• chimaeras

• diphycercal caudal fin

• no scales

• teeth = grinding plates

• digestive system
  1. no stomach
  2. liver/ gall bladder/ pancreas; all present

• respiratory system
  (gills/ operculum present over some)

• no swim bladder

• nervous system (see above)

• sensory (see above)

• reproductive
  1. dioecious
  2. urogential opening

• fert ext.

The bony fishes, the largest and most diverse taxon of all vertebrates, originated in the late Silurian, approximately 410 million years ago.

• 2 subclasses
  1. Subclass Actinopterygii (ray-finned fishes)
  2. Subclass Sarcopterygii (fleshy-finned fishes)

• bony fishes

• bony endoskeleton

• homocercal caudal fin

• 3 scale types (ganoid, ctenoid, cycloid)

• mucus glands

• dorsal fins; anal fin; paired others

• mouth terminal

• respiratory system gills; operculum; counter current

• swim bladder present
  1. with/without duct
  2. neutral buoyancy

• circulatory system
  1. nervous system
  2. brain (p. 510 for more)

• sensory
  1. vision
  2. smell
  3. lateral line

• excretory system
  1. kidneys
  2. osmotic reguation
     (marine vs FW)
  3. euryhaline/stenohaline

• nutrition
  1. carnivores
  2. herbivores
  3. omnivores
  4. suspension feeders
  5. scavengers
  6. parasites

• movement throught the water

• migration
  1. eels
     Salmon

• reproductive system
  (dioecious)

• ovoviviparous; viviparous; oviparous

• ext. fert. mostly

• growth
  1. indeterminate
  2. temp dependent

Once you have completed the lesson, you should go to Assignment 27-1.

E-mail Sylvester Allred at

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