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FISHES. Agnatha Chondrichthyes Osteichthyes. General Characteristics. Ectothermic Vertebrates Have scales Swim with fins Almost all exclusively aquatic Filter oxygen from water over gills. Classes of Fish. Agnatha – Jawless Fish Chondrichthyes – Cartilagenous Fish
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FISHES Agnatha Chondrichthyes Osteichthyes
General Characteristics • Ectothermic • Vertebrates • Have scales • Swim with fins • Almost all exclusively aquatic • Filter oxygen from water over gills
Classes of Fish • Agnatha – Jawless Fish • Chondrichthyes – Cartilagenous Fish • Osteichthyes – Bony Fish
Question #1: • What is the name for a person who studies fishes? • Ichthyologist
Early Fish • Earliest - Filter feeders, no jaws, no fins • Ostracoderms – jawless, heavy bony plates • Lobe finned fishes – Coelocanths
Fins • Caudal – propels fish forward • Dorsal – stabilizer • Anal – stabilizer • Pectoral – hold fish steady, maneuvering • Pelvic – hold fish steady, maneuvering
Scale Types • Cycloid – smooth surface, on bony fish • Carp • Salmon • Ctenoid – teeth along ridge (rough to touch), on bony fish • Bass • Bluegill • Perch
Scale Types • Placoid – Look like tiny teeth, feel like sandpaper, on cartilagenous fish • Sharks • Rays • Ganoid – hard, interlocking, diamond-shaped, on primitive fish • Gar
Question #2: • What is the purpose of a fish’s scales? • Shield against injury, help to move through the water
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
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
Gills • Obtain oxygen • Give off carbon dioxide • Most have an operculum • Oxygen dropped into circulatory system pumped by 2-chambered heart
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
Freshwater fishes never drink Lots of nephrons Ions are reabsorbed Marine fishes Drink constantly Less blood is filtered Water is reabsorbed Excretion and Osmoregulation
Senses • Limited vision, focus by moving lens back and forth • Olfactory receptors • Magnetic receptors • Touch
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
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
Class Agnatha • Cartilagenous • Simplest and oldest vertebrates • Jawless • No scales • Scavengers or parasites • Lamprey, hagfish
Class Chondrichthyes • Hinged jaw • Paired fins • Scales • Muscles attached to skin, not skeleton • Cartilagenous skeleton
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
Skates and Rays • Wing-like pectorals • Most live on sea beds • Some have poison spines on backs or tails (stingrays)
Class Osteichthyes • Largest group of fishes • Skeleton made of bone and cartilage • Hinged jaws • Paired fins • Hard, protective scales • Covered gills (operculum)
Major Groups of Osteichthyes • Subclass Sarcopterygii • Lobe-finned fishes (Coelocanth) • Lungfishes • Subclass Actinopterygii – • Ray-finned fishes • Bass • Tuna • Guppies