The Classes
of Fish
Class
Agnatha: (Lamprey and
Hagfish)
General
Characteristics:
- Absence of jaws.
- These organisms lack the
paired fins (pelvic and
pectoral).
- Skeleton made of
cartilage.
- Round eel-like body with a
compressed caudal fin.
- Soft skin devoid of
scales.
- They lack a swim bladder and
gill covers
(operculum).
- 7 gill slits on each side of
the head.
- The lamprey are parasitic and
the hagfish are scavengers.
- Ectothermic
( animals that cannot control their body temperature).
- External fertilization.
Oviparous
(egg laying)
- Marine and fresh water species
are found.
- Lateral line
- Two chambered
heart
- Gills used for
respiration
- No external ears
- No eye lids
Class
Chondrichthyes: (Sharks,
Rays, and Skates).
General
Characteristics:
- Skeleton made of
cartilage.
- Body covered with triangular
Placoid
scales.
- Ventral,subterminal mouth with
several rows of triangular teeth.
- Large caudal fin with the
dorsal section larger than the ventral one.
- Paired fins (pectoral and
pelvic), are stiff and nonflexable.
- They lack a swim
bladder.
- Ectothermic
- Internal fertilization.
Ovoviviparous (developing egg kept inside the female for
protection and does not live off of the parent).
- Marine organisms
only.
- Lateral line
- Two chambered
heart
- Gills used for
respiration
- No external ears
- No eye lids
Class Osteichthyes: (Tuna,
Carp, Salmon, and Sturgeons).
General
Characteristics:
- Skeleton made of
bone
- Lateral line
- Two chambered
heart
- Operculum covering the
gills.
- Swim bladder
- Ectothermic
- Paired fins made of rays and
spines,or lobed fins
lacking the rays and
spines.
- Various types of scales
(ctenoid,ganoid, or cycloid).
- Marine and fresh water
species.
- Gills used for
respiration
- External fertilization.
Spawning. Oviparous.
- No external ears
- No eye lids.
Fish heart

a. atrium b. ventricle
Fish Internal
Organs

Fish Brain

1. Olfactory Lobes : Functions in
smell.
2. Cerebrum : Functions in muscle
movement, intelligence, instinct, and will power.
3. Optic Lobes : Functions in eye
sight.
4. Cerebellum : Functions in
muscular coordination.
5. Medulla Oblongata : Functions
in involuntary responses ( heart beat, breathing, and digestion
).
6. Spinal Cord : Functions in
transport of nerve impulses to and from the brain.