ichthyology n.
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Ichthyology. The study of fishes. Over half of all vertebrates are fishes! Fishes have the following 5 characteristics in common: Vertebral column : internal skeleton spine surrounding the dorsal nerve cord

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The study of fishes


Over half of all vertebrates are fishes!

    • Fishes have the following 5 characteristics in common:
      • Vertebral column: internal skeleton spine surrounding the dorsal nerve cord
      • Jaws and paired appendages: all fish except lampreys and hagfishes have both. Jaws allow fishes to eat things bigger then their mouths
      • Internal Gills: used for respiration
      • Single-loop blood circulation: blood goes from heart to gills to rest of body and back to heart
      • Nutritional deficiencies: unable to make certain amino acids and must consume them (just like all of their vertebrate descendants!)

Evolution of the jaw:

    • Fundamentally important evolutionary advance
    • Evolved from the most anterior of a series of gill arches

The evolution of shark teeth:

    • Sharks were among the first vertebrates to develop teeth
    • Evolved from rough scales on the skin and are not set into the jaw like human teeth
      • Not firmly anchored and easily lost
      • A shark may loose more than 20,000 teeth in it’s lifetime

The Lateral Line System:

    • Supplements the fish’s sense of hearing (yes, fish have ears too)
    • Series of canals running length of the body
    • Within these canals are hair cells with cilia that detect water movement
    • This what enables the fish to detect prey and swim in synchrony with it’s school

The Swim Bladder

    • Gas-filled sac that allows bony fish to regulate their buoyant density and adjust their depth effortlessly
    • Organs are filled and drained of nitrogen and oxygen internally


    • Fish allow water to flow over the gills for gas exchange
    • Bony fish have an operculum
      • Hard plate covering the gills
      • Bony fish can pump water over their gills, sharks can not

Fish are divided into 7 classes:

  • Sarcopterygii, lobe-finned fishes
  • Actinopterygii, Ray-finned fishes
  • Chondrichthyes, Sharks and rays
  • Cephalaspidomorphi, Lampreys
  • Myxini, Hagfishes
  • Placodermi, Armored fishes
  • Acanthodii & Ostracoderms, Spiny fishes

Class Myxini: The Hagfishes