Fish Notes
Sharks
• Class: Chondrichthyes – skeleton made of
cartilage & tooth-like scales covering their
skin.
Characteristics
1.Placoid scales – have a
pointed tip which faces
backwards. (denticles)
2.Heterocercal tail – upper
lobe is longer than the
lower lobe.
3. Gill slits not covered by
an operculum (5-7 gill
slits)
Characteristics, cont’d
4. Can’t swim backwards
5. Sharks have no swim bladder so
they sink – to compensate they
have a very oily liver – it can be up
to 25% of their body mass.
6.Sharks vary greatly in size
7.Smallest –dwarf shark 6-8 inches
Largest – whale shark 60 feet
Teeth
Senses
– some species can go through 20,000 teeth in
a lifetime.
– Broken teeth are replaced from those behind –
like a conveyor belt.
Senses
Ampullae of Lorenzini –
hundreds of tiny holes in
the face of a shark which
helps them pick up
electrical impulses given off
by living prey items.
Hearing – best sense – can
hear prey in the water from
3,000 feet away.
Lateral line – detects
differences in water pressure
to help fish detect obstacles
in their path.
Senses
Smell – well developed. They
can detect 1 part blood per
100 million parts of water.
2/3rds of brain devoted to
sense of smell
Eyesight - certain sharks have
evolved a special
"nictitating membrane" on
the lower lid of the eye that
protects the eye from
thrashing fish during
feeding frenzies. They can
see well in low light.
Shark Attack!!
• Shark Attack – 25 species
have attacked man
– 3 most dangerous are Great
White Shark, Tiger Shark
and the Bull Shark
– Chance of being attacked is
less than being hit by
lightning.
– Most likely to attack in
shallow water (less than 4
feet)
– If attacked hit on nose or
stick fingers in gills or eyes!