Biology of Fish
Fish belong to the group Chordata
Includes around 52,000 species
including fish, mammals,
reptiles, etc.
Characteristics of Chordates
• Chordates: named for the notochord structure
found in all chordate embryos. Chordate
embryos also share:
1. Hollow, dorsal nerve cord (becomes brain and
spinal cord)
2. Have slits in the pharynx (behind the mouth)
3. Tail that extends beyond the anus
4. (possesses a notochord)
• Notochord: flexible rod that extends through the
length of the body
Chordates - Fish
Diversity of Fish
• Fish were the 1st jawed vertebrates
• Make up 30,000 of the +52,000 species of
vertebrates
• Two main groups of fish:
1. Cartilaginous fish: skeleton made of cartilage
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Ex. sharks and rays
One class Chondrichthyes
2. Bony fish: skeletons contain bone hardened by
calcium compounds
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Ex. ray finned fish, coelacanths, a lungfish, tilapia,
salmon
Class: Osteichthyes
Three subclasses: Actinopterygii, Actinistia,
Dipnoi
Sharks vs. Fish
Attributes
Sharks
Fish
Skeleton
Cartilage only
Bones and cartilage
Swimming
Can only swim
forward
Large oily liver
Buoyancy
Skin
Gills
Swim forwards and
backwards
Gas-filled swim
bladder
Rough, sandpaperSlippery,
like scales
overlapping scales
Gill slits, but no gill
cover
Covered gill slits
Chondricthyes (Sharks, rays, and ratfishes)
• 850 species
• Bony skeleton replaced with
flexible cartilage for buoyancy
• no swim bladder
• exposed gill slits
• have well developed sensory
organs
Osteichthyans (bony fish)
Actinopterigii (ray-finned fish)
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•
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Flexible rays support fins
Operculum flap protects and ventilates gills
Air-filled swim bladder regulates buoyancy
Skin contains bony scales and lateral line pits
Most are oviparous (lay eggs) with external fertilization,
but many reproductive strategies can be found in this
group including hermaphrodites capable of cloning
themselves and species who give birth to live young
swim bladder
gills
operculum
lateral
line
Actinistia (lobe-finned fish)
• Includes the coelacanth and tetrapod lineages
• Thick muscles of pectoral and pelvic fins surround rod-shaped
bones (have paddle like fins with fleshy bases)
• Coelacanths were thought to be extinct until 1938 when they
were discovered of the coast of east Africa. Since then a second
population has been found in Indonesia
Dipnoi (Lungfish)
• Found only in Southern
Hemisphere
• Adaptation to Air Sac that
can function as lungs
during periods of drought.
• Also have gills to obtain
oxygen from water.
• They burrow into the mud
and cover themselves in
mucus to stay moist until
the pond refills.
What do fish need?
• Clean Water: Good pH, low ammonia, no harmful
chemicals
• Oxygen: Take in oxygen dissolved in water
• Food: Need high amount of protein
• Proper Temperature: Fish are cold-blooded, so
metabolism slows in cold temps
• Proper Salinity: Depends on freshwater or saltwater
Fish Anatomy
• Lateral line: sensory organs running along the
body help sense changes in water pressure (feel
other animals)
• Gills: extract oxygen from the surrounding water
• Swim Bladder: aids in “hearing” for many fish
and transmits vibrations to sensory organs
(sharks use electromagnetic fields), the lungfish
use these as a respiratory organ to breath air
• Fins: swimming and defense
Fish External Anatomy - Fins
Fish External Anatomy - Fins
• Caudal fin - used for forward propulsion of the fish.
• Soft dorsal fin - may be used for forward propulsion and as a
rutter to change direction.
• Spiny dorsal fin - used as a keel to maintain fish balance. Can
be lowered to increase streamlining of fish (increase
swimming speed)
• Pectoral fin - used for braking and turning while swimming
and may be used for forward propulsion.
• Pelvic fin - prevents fish from floating upward when fish
brakes (with pectoral fins)
• Anal fin - acts as a rudder for turning, may be used for
forward propulsion.
Fish Internal Anatomy
What are the parts of the fish digestive system?
• The digestive system is similar to other
animals.
• Size and shape of each component of the
system will vary with the type of fish and
its diet.
• Carnivores
– Fish that eats meat.
– Have a large stomach and short intestines.
What are the parts of the fish digestive system?
• Parts include:
– Mouth
• Teeth
• Tongue
• Branchiospines
– Esophagus
– Stomach
– Intestines
– Anus
What are the parts of the fish digestive system?
• Mouth
– Entry point of system.
• Carnivores mouth
– Have many teeth that point
inwards.
– Not used for chewing.
– Used to capture and hold
prey.
• Other fish
– Few or no teeth.
What are the parts of the fish digestive system?
• Tongue
– Helps move food around in the
mouth.
• Branchiospines
– Act as filters to capture small
food from water as the fish
swims.
– Part of the gill structure that
helps fish swim.
• Esophagus
– Short tube that connects mouth
to stomach.
What are the parts of the fish digestive system?
• Stomach
– Organ where digestion begins.
– Some stomachs will expand greatly.
• Allows them to eat large quantities of
food.
– Other stomachs are small that will
accommodate small amounts of food.
– Some fish have almost no stomach.
• Esophagus connects directly to
intestines.
What are the parts of the fish digestive system?
• Intestines
– Site of food digestion and nutrient
absorption.
– Herbivorous have longer intestines
than that of carnivorous animals.
This is because their diet is made up
of fiber and cellulose that is hard to
digest. This means that the
herbivorous need a longer digestive
track to digest their foods
completely.
• Anus
– Exterior opening of system.
– Unused food and wasted material is
exited.
Nervous/Muscular System
• Nervous System
• Relatively simple system
• Central Nervous System
– Brain and Spinal Cord
• Peripheral Nervous System
– Cranial Nerves and Spinal Nerves
• Muscular System
• Muscle segments in the shape of “W”
• Muscle is the edible part
of the fish
Circulatory/Respiratory System
Heart and Blood Vessels
• 2 chambered heart: distributes O2 in the body
– Atria-collects blood from body
– Ventricle-sends blood to the gills
– Humans have a 4 chambered heart – fish need less 02
• Arteries: carry blood away
from the heart
• Veins carry blood back to
the heart
Gills
• Blood-filled membranes
that exchange oxygen and
carbon dioxide
• Like the lungs in a human
EXIT SLIP-January 29, 2014
• 1. What is one difference between
Cartilaginous Fish and Bony Fish?
• 2. What are the three groups of Bony Fish?
• 3. How does a fish’s heart differ from
humans?
• 4. What type of Bony fish is a Tilapia?
• 5. What organ allows a fish to stay motionless
in the water without sinking?