FISHES

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FISHES

• Agnatha
• Chondrichthyes
• Osteichthyes

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General Characteristics

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

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Classes of Fish

• Agnatha Jawless Fish
• Chondrichthyes Cartilagenous Fish
• Osteichthyes Bony Fish

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Question 1

• What is the name for a person who studies fishes?
• Ichthyologist

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Early Fish

• Earliest - Filter feeders, no jaws, no fins
• Ostracoderms jawless, heavy bony plates
• Lobe finned fishes Coelocanths

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Fish Anatomy
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Fins

• Caudal propels fish forward
• Dorsal stabilizer
• Anal stabilizer
• Pectoral hold fish steady, maneuvering
• Pelvic hold fish steady, maneuvering

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Scale Types

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

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Scale Types

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

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Question 2

• What is the purpose of a fishs scales?
• Shield against injury, help to move through the
  water

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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

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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

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Gills

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

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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

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Countercurrent Exchange System
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Excretion and Osmoregulation

• Freshwater fishes
• never drink
• Lots of nephrons
• Ions are reabsorbed

• Marine fishes
• Drink constantly
• Less blood is filtered
• Water is reabsorbed

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Senses

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

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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

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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

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Class Agnatha

• Cartilagenous
• Simplest and oldest vertebrates
• Jawless
• No scales
• Scavengers or parasites
• Lamprey, hagfish

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Class Chondrichthyes

• Hinged jaw
• Paired fins
• Scales
• Muscles attached to skin, not skeleton
• Cartilagenous skeleton

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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

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Skates and Rays

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

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Class Osteichthyes

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

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Major Groups of Osteichthyes

• Subclass Sarcopterygii
• Lobe-finned fishes (Coelocanth)
• Lungfishes
• Subclass Actinopterygii
• Ray-finned fishes
• Bass
• Tuna
• Guppies