Fishes

Fish Classification

Subphylum Craniata

• Infraphylum Hyperotreti (Hagfishes)

  • Class Myxini

• Infraphylum Vertebrata

  • Superclass Petromyzontomorphi (Lampreys)

  • Superclass Gnathostomata

    • class Chondrichthyes (sharks, skates, rays, ratfish)

    • class Sarcopterygii (lobe-fined fishes)

    • class Actinopterygii (ray-fined fishes)

    • class Amphibia (amphibians)

    • class Reptilia (reptiles)

    • class Aves (birds)

    • class Mammalia (mammals)

Class Myxini (Hagfishes)

• most primitive craniates

  • lack vertebrae

  • retain notochord

  • jawless

• slime glands

• cold water habitats

• live buried in sediment

• scavenge dead fish

Class Petromyzontida (Lampreys)

• common in temperate oceans

• most adults prey on other fish

• jawless, sucker mouth

• rasp-like tongue

• ectoparasite

• invasive species in the Great Lakes

  • allowed in through artificial connections

Superclass Gnathostomata

• jawed vertebrates

• jaws evolved from the anterior pharyngeal arches

  • permitted more efficient gill ventilation

  • facilitated the capture and ingestion of prey

• paired appendages

  • advantages?

    • provided stability, which facilitated more activity

• both traits (jaws and paired appendages) contributed to predatory lifestyle

  • how did this affect evolutionary radiation?

    • allowed fish to produce more offspring

      • fueled radiation during Devonian period (age of the fishes)

Class Chondrichthyes

• sharks, skates, rays, ratfish

• carnivores and scavengers

• cartilaginous endoskeleton

• placoid scales (hard dentine)

• constant production of teeth (modified scales)

Evolutionary Pressures and Adaptations

• locomotion

  • water is a dense medium

    • adaptations?

      • stream-lined shape

      • mucous secretions

      • buoyancy measures save energy for movement

        • swim bladder

        • gases secreted from blood through gas gland

• nutrition and digestion

  • swallow prey whole

  • create negative pressure to suck prey in

  • large stomach to store infrequent meals

  • filter-feeding fish have gill rakers

• sensory function

  • receptors for balance and hearing in inner ear

  • lateral line system

    • sensory pits in epidermis

      • stimulated by water movement

      • can detect predators and prey

• gas exchange

  • water contains <2.5% of the oxygen found in the air

  • fish must pass large quantities of water over gills (epithelial tissue)

  • “countercurrent exchange”

Class Actinopterygii

• ray-fined fishes

  • chondrosteans (sturgeon)

    • bony plates called scutes

    • ancient

  • teleosts

    • modern bony fishes

    • 24,000 species

Class Sarcopterygii

• lobe-finned fish

  • coelacanth

    • thought to be extinct

    • in the last 50 years, they have been rediscovered

    • deepwater off Madagascar and Indonesia

• lungfish

  • live in regions with drought/stagnation

    • why might this lead to evolution of air breathing?

  • usually use lungs for gas exchange

    • can remain in aestivation for 6 months

• likely predecessor to tetrapods (air and lobed-fins)