FISHES
Agnatha
Chondrichthyes
Osteichthyes
General Characteristics
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Ectothermic
Vertebrates
Have scales
Swim with fins
Almost all exclusively aquatic
Filter oxygen from water over gills
Classes of Fish
– Jawless Fish
 Chondrichthyes –
Cartilagenous Fish
 Osteichthyes – Bony Fish
 Agnatha
Question #1:
 What
is the name for a person
who studies fishes?
 Ichthyologist
Early Fish
 Earliest
- Filter feeders, no jaws, no
fins
 Ostracoderms – jawless, heavy bony
plates
 Lobe finned fishes – Coelocanths
Fish Anatomy
Fins
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Caudal – propels fish forward
Dorsal – stabilizer
Anal – stabilizer
Pectoral – hold fish steady, maneuvering
Pelvic – hold fish steady, maneuvering
Scale Types

Cycloid – smooth surface, on bony fish
–
–

Carp
Salmon
Ctenoid – teeth along ridge (rough to
touch), on bony fish
–
–
–
Bass
Bluegill
Perch
Scale Types
– Look like tiny teeth, feel
like sandpaper, on cartilagenous fish
 Placoid
Sharks
– Rays
–
– hard, interlocking,
diamond-shaped, on primitive fish
 Ganoid
–
Gar
Question #2:


What is the purpose of a fish’s scales?
Shield against injury, help to move through the
water
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
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
Gills
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Obtain oxygen
Give off carbon dioxide
Most have an operculum
Oxygen dropped into circulatory system
pumped by 2-chambered heart
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

Countercurrent Exchange System
Excretion and Osmoregulation
 Freshwater
fishes
never drink
– Lots of
nephrons
– Ions are
reabsorbed
–
 Marine
fishes
Drink constantly
– Less blood is
filtered
– Water is
reabsorbed
–
Senses
 Limited
vision, focus by moving
lens back and forth
 Olfactory receptors
 Magnetic receptors
 Touch
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
Reproduction

Oviparous (most fish)
–

Ovoviviparous (some cartilaginous fishes)
–
–
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Release eggs, young develop outside mom
Eggs remain inside mom
Eggs at a later stage of development before they
are released
Viviparous (a few sharks)
–
Young born alive
Class Agnatha
Cartilagenous
 Simplest and oldest vertebrates
 Jawless
 No scales
 Scavengers or parasites
 Lamprey, hagfish

Class Chondrichthyes
 Hinged
jaw
 Paired fins
 Scales
 Muscles attached to skin, not
skeleton
 Cartilagenous skeleton
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
Skates and Rays
 Wing-like
pectorals
 Most live on sea beds
 Some have poison spines on backs
or tails (stingrays)
Class Osteichthyes
 Largest
group of fishes
 Skeleton made of bone and cartilage
 Hinged jaws
 Paired fins
 Hard, protective scales
 Covered gills (operculum)
Major Groups of Osteichthyes

Subclass Sarcopterygii
–
–
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Lobe-finned fishes (Coelocanth)
Lungfishes
Subclass Actinopterygii –
–
Ray-finned fishes
 Bass
 Tuna
 Guppies