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FISHES
There are 3 main groups of fish:
1.Agnatha – jawless fish
2.Chondrichthyes – cartilaginous fish
3.Osteichthyes – bony fish
I.
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.
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.) Teeth are modified scales.
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).
8. Kidneys and rectal glands for
excretion.
9. No swim bladder, liver filled
with oil aids in buoyancy.
10. Sexes separate. Fertilization
internal. Mostly egg laying, some
with live birth.
Mola mola
Humuhumunukunukuapu’aa
Salmon - spawning
III. 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, many teeth.
4. Paired fins with rays (bones) and a
homocercal tail.
5. Gills for respiration, covered by
operculum (protects and facilitates
water entry.
6. Circulatory system –
Path of blood flow : heart (atrium to
ventricle) -> gills (pick up oxygen) ->
dorsal aorta -> body -> ventral veins ->
heart.
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.
10. Digestion: Alimentary canal includes
mouth -> pharynx -> esophagus ->
stomach -> intestine -> cloaca -> anus.
Accessory organs include pancreas, gall
bladder, liver.
Mainly carnivores and eat any kinds
of aquatic animals.
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.