Fish Physiology

Class Myxini and Class Petromyzontida—Hagfish and Lampreys

• Primitive

• Smooth and scaleless, mucus coating

• Cartilaginous skeleton

• Lack paired appendages

• 5-15 pairs of external gill openings

• Lampreys—oral disk lined with teeth—parasitic

• Hagfish—2 dental plates—scavengers

Gnathostome Fishes—jawed fishes

• Hinged jaws—wider variety of prey

• Paired fins—increased stability

• Chondrichthyes—cartilaginous fishes

• Teleostomi—bony fishes

Class Chondrichthes

• Cartilaginous skeleton

• Placoid scales with a spine of dentin

• Skates and Rays—bottom-living, enlarged pectoral fins fused to the head, horizontal gill openings, eyes on top othe f head

  • skates—muscular tail, two dorsal fins, lay eggs

  • Rays—no dorsal fins, live birth

• Sharks—5-7 vertical gill slits, moth birth live young, pectoral fins not fused to the head

Grade Teleostomi

• Two classes

  • Sarcopterygii—lobe-finned fishes

    • Coelacanths, lungfishes

    • Muscular, lobed, paired fins

  • Actinopyterygii—ray-finned fishes

Teleostomi Integument

• Ganoid scales—rhomboid shape, composed of bone

  • Sturgeon, paddlefish, gar

• Cycloid scales and Ctenoid scales—outer layer of bone, inner layer of connective tissue, concentric ridges that represent growth increments

  • Ctenoid scales—comblike serrated edges

  • Cycloid scales—smooth margins

  • Chromatophores—pigment-bearing cells

  • Photophores—light-emitting cells (looks like it glows in the dark)

Circulation and Respiration

• 2 chambered heart

• Blood flows through heart 1x in circuit of body

• Low-pressure flow

• Gills—filaments and lamella

  • Countercurrent flow

  • Operculum in teleost fish

Digestion

• Many different feeding strategies

  • filter feeders

  • herbivores

  • detritivores

  • carnivores

  • omnivores

• Mouth > pharynx > esophagus > stomach > pyloric caeca > intestines > colon > vent

• 

Excretion

• Fish kidney is like embryonic kidney of reptiles, birds, and mammals

• Small urinary bladder

• Most excrete ammonia

• Parts of excretory system also function in reproduction

  • sperm storage