FISHES

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FISHES
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• There are 3 main groups of fish
• Agnatha jawless fish
• Chondrichthyes cartilaginous fish
• Osteichthyes bony fish

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• Agnatha (without jaws)
• A. Examples Lampreys and hagfish
• B. Characteristics
• 1. Skeleton of cartilage. Retain notochord
  throughout life.
• 2. Two chambered heart.
• 3. Small brain.
• 4. No jaws.
• 5. Scavengers or parasites.

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• II. Chondrichthyes (cartilage fish)
• A. Examples Sharks and Rays

B. Characteristics 1. Skeleton of
Cartilage. 2. Body streamlined with
heterocercal tail and paired pectoral and
pelvic fins.
3. Skin with placoid scales. Scales are very
small and rough (once used as sandpaper.)and are
toothlike. Teeth are modified scales.
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4. Alimentary canal with ventral mouth,
J-shaped stomach, spiral valve in intestine.
Most are carnivores.  

5. Exposed gills for respiration. 6. Two
chambered heart.
7. Well developed brain. Senses - smell,
vibration reception (lateral line system),
electroreception (ampullae of Lorenzini), and
vision. Semicircular canals (in ear area) for
body orientation (like statocysts).
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• Kidneys and rectal glands for
• excretion (filter blood and
• excrete urine).

• 9. No swim bladder, liver filled
• with oil aids in buoyancy.
• 10. Sexes separate. Fertilization
• internal. Mostly egg laying, some with live
  birth.

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Mola mola
Humuhumunukunukuapuaa
Salmon - spawning
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• Osteichthyes (bony fish)
• A. Examples Salmon, Tuna, Sunfish, etc.
• B. Characteristics
• 1. Skeleton of bone
• 2. Skin with scales (geometrically
  shaped and overlapping) and mucus glands.
• 3. Mouth terminal (at the end),
• many teeth.

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• 4. Paired fins with rays (bones) and a
• homocercal tail.
• 5. Gills for respiration, covered by operculum
  (protects, facilitates water entry).
• 6. Circulatory system
• Path of blood flow heart (atrium to
  ventricle) -gt gills (pick up oxygen) -gt
  dorsal aorta -gt body -gt ventral veins -gt heart.

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• 7. Nervous System Brain and
• dorsal nerve cord. Senses
• include smell, vision, lateral line,
• touch.
• 8. Segmented muscles with very
• flexible body.
• 9. Swim bladder for buoyancy.

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• 10. Digestion Alimentary canal includes mouth
  -gt pharynx -gt esophagus -gt stomach -gt intestine
  -gt cloaca -gt anus. Accessory organs include
  pancreas, gall bladder, liver.
• 11. Mainly carnivores and eat any kinds of
  aquatic animals.

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12. Reproduction Most dioecious with external
fertilization. These lay eggs. Some have
internal fertilization. Weird fact
Sheepshead are all born female. Some will
change into males depending on circumstances..
Hence they are considered hermaphroditic.
13. Bony fish live in any type of water
fresh, salt, marshy, brackish, etc.