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Understanding Fish: Structure, Function & Behavior

Dive into the world of fishes with this comprehensive guide covering their anatomy, behavior, and characteristics. Learn about the different classes of fish, their unique adaptations, and how they navigate their aquatic environments.

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Understanding Fish: Structure, Function & Behavior

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  1. FISHES Agnatha Chondrichthyes Osteichthyes

  2. General Characteristics • Ectothermic • Vertebrates • Have scales • Swim with fins • Almost all exclusively aquatic • Filter oxygen from water over gills

  3. Classes of Fish • Agnatha – Jawless Fish • Chondrichthyes – Cartilagenous Fish • Osteichthyes – Bony Fish

  4. Question #1: • What is the name for a person who studies fishes? • Ichthyologist

  5. Early Fish • Earliest - Filter feeders, no jaws, no fins • Ostracoderms – jawless, heavy bony plates • Lobe finned fishes – Coelocanths

  6. Fish Anatomy

  7. Fins • Caudal – propels fish forward • Dorsal – stabilizer • Anal – stabilizer • Pectoral – hold fish steady, maneuvering • Pelvic – hold fish steady, maneuvering

  8. Scale Types • Cycloid – smooth surface, on bony fish • Carp • Salmon • Ctenoid – teeth along ridge (rough to touch), on bony fish • Bass • Bluegill • Perch

  9. Scale Types • Placoid – Look like tiny teeth, feel like sandpaper, on cartilagenous fish • Sharks • Rays • Ganoid – hard, interlocking, diamond-shaped, on primitive fish • Gar

  10. Question #2: • What is the purpose of a fish’s scales? • Shield against injury, help to move through the water

  11. Maintaining Buoyancy • Swim bladder • Uses air • Most bony fishes • Can be used as a second “lung” • Liver • Uses oil • Sharks • Most sharks must constantly swim to avoid sinking

  12. Locomotion • Use fins and body wall to push against water • Forked tails reduce drag in the water • Muscles in a zig-zag shape • Each contraction moves large parts of the body wall

  13. Gills • Obtain oxygen • Give off carbon dioxide • Most have an operculum • Oxygen dropped into circulatory system pumped by 2-chambered heart

  14. Gas Exchange • Pump ventilation • Ram ventilation • Exchange of gases occurs in capillary network in gill lamellae; water and blood flow in opposite directions over lamellae = Countercurrent Exchange

  15. Countercurrent Exchange System

  16. Freshwater fishes never drink Lots of nephrons Ions are reabsorbed Marine fishes Drink constantly Less blood is filtered Water is reabsorbed Excretion and Osmoregulation

  17. Senses • Limited vision, focus by moving lens back and forth • Olfactory receptors • Magnetic receptors • Touch

  18. Sense (cont.) • Hearing – sound conducted through skull • Lateral line system – senses movement of other organisms around them • Electroreception – sense electrical impulses generated by muscle twitches

  19. Reproduction • Oviparous (most fish) • Release eggs, young develop outside mom • Ovoviviparous (some cartilaginous fishes) • Eggs remain inside mom • Eggs at a later stage of development before they are released • Viviparous (a few sharks) • Young born alive

  20. Class Agnatha • Cartilagenous • Simplest and oldest vertebrates • Jawless • No scales • Scavengers or parasites • Lamprey, hagfish

  21. Class Chondrichthyes • Hinged jaw • Paired fins • Scales • Muscles attached to skin, not skeleton • Cartilagenous skeleton

  22. Sharks • Jaws not attached to brain case • Can protrude during attack • 20 tons per square inch for an 8’ shark • Size varies (few inches to over 40 feet) • Variable body shapes

  23. Skates and Rays • Wing-like pectorals • Most live on sea beds • Some have poison spines on backs or tails (stingrays)

  24. Class Osteichthyes • Largest group of fishes • Skeleton made of bone and cartilage • Hinged jaws • Paired fins • Hard, protective scales • Covered gills (operculum)

  25. Major Groups of Osteichthyes • Subclass Sarcopterygii • Lobe-finned fishes (Coelocanth) • Lungfishes • Subclass Actinopterygii – • Ray-finned fishes • Bass • Tuna • Guppies

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