External Anatomy of Fish
The Head
Mouth Shape/ Position
•Superior Mouth
–Also known as an undershot or
upturned mouth
–Eats food above the fish
–May eat at the water’s surface
•Terminal Mouth
–Eats food in front of it
•Inferior Mouth
–Also known as an underslung
mouth
–Eats food below it
–May eat off of the bottom
Operculum & Gills
• Gills
– Allows gas exchange for the fish
– Through the gills, fish are able to absorb
oxygen and give off carbon dioxide
• Operculum
– The gill cover
Barbels
• Also known as whiskers
• located under the mouth of a fish
• are tactile and taste organs used for
locating food in dark or muddy waters
The Body
Body shapes
•Ovate Body
–Slow swimmer
–Difficult for predators to
swallow
•Fusiform Body
–High speed swimmers
–The most common form
•Truncate
–A shortened type of
fusiform
•Elongate/Serpentine
–Hides in rocks and weeds
Body Covering
• covered with scales, which protect the
body
• Most fish get extra protection from a
layer of slime that covers their scales
called mucus.
Scales
• Made of calcium, they are outgrowths of the
skin
• They overlap like shingles on a roof so that
the skin of the fish is not exposed
• The scales of a fish lie in pockets in the
dermis and come out of the connective
tissue.
• Scales do not stick out of a fish but are
covered by the Epithelial layer.
• The ridges and the spaces on some types of
scales become records of age and growth
rate.
Types of Scales
•Cycloid scales
–Have a smooth edge
on the backside
–Found on soft-rayed
fish
•Ctenoid scales
–Have teeth-like
projections along the
backside
–Found on spiny-rayed
scales
•Placoid scales
–Are similar to teeth
–Made of dentin
covered by enamel
•Ganoid scales
–Flat and basal looking
–They overlap very
little
Mucus (Slime)
• helps them move through the water
better by reducing friction
• is a barrier to the entry of parasites,
fungi, and disease organisms that
might infest the fish
• it seals in the fish’s body fluids so that
they are not diluted by the watery
surroundings
• makes the fish slippery when predators
try to grab hold
Lateral Line
• is a series of fluid-filled ducts located just
under the scales
• picks up vibrations in the water
– fish are able to detect predators, find food, and
navigate more efficiently
• help the fish detect water pressure changes
• It can detect minute electrical currents in the
water
• It runs in a semi line from the gills to the tail
fin. It can be easily seen in fish as a band of
darker looking scales running along the side.
Peduncle
• The edge of the tail fin that lies on the
end or outside of the caudal fin
Types of Fins
Fins
• used for movement, stability, nestbuilding, spawning, and as tactile
organs
• can be single or paired
Tail fin
• Also known as the caudal fin
• Used for propulsion
• Large, elongated caudal fins are often
used to attract mates.
Types of Caudal Fins
•Heterocercal Tail
–the vertebrae extend into a
larger lobe of the tail or that
the tail is asymmetrical
•Fast swimmer
•Constantly moving
•Two types
–Epicercal means that the
upper lobe is longer
–Hypocercal means that
the lower lobe is longer
•Protocercal Tail
–the caudal fin extends
around the vertebral
column
•Slow swimmer
•Bottom wriggler
•Diphycercal Tail
–three-lobed caudal fin
–the vertebrae extend all
the way to the end of the
tail
•Homocercal Tail
–the vertebrae do not extend
into a lobe and the fin is more
or less symmetrical
•Rounded
–Good at turning
–Fast for short distances
–Often predators
•Truncate Tail
–Good at turning
–Slower swimmer
•Forked Tail
–Fast swimmer
•Lunate Tail
–Long distance swimmer
Anal Fin
• A single fin
• Located on the underside of the body
just forward of the caudal fin
• Used to stabilize the fish while it is
swimming
• Long anal fins that are moved in an
undulating manner are used for
propulsion
Pelvic or Ventral Fins
• A paired fin
• located forward of the anal fin
• are used to provide further stability in
swimming
• times these fins are modified as long,
thread-like fins used as a tactile organ
• Relate to the hind legs
Pectoral Fin
•
•
•
•
A paired fin
located near the gill cover
used for manoeuvring the fish
Sometimes the pectoral fins are
equipped with spines for defence
• Related to the front legs or arms
Dorsal fin
• A single fin, but some species may have
a second fin
• located on the back of the fish
• serves to help balance the fish while
swimming
• rays of this fin are often sharp, and a
spine is often present
Adipose fin
• is a tiny fin found between the dorsal
and caudal fins on some fish
• a soft, fleshy fin
Finlets
• small fins
• generally behind the dorsal and anal
fins
• they are rayless and non-retractable
Caudal Keel
•
•
•
•
May be single, paired, or double pairs
a lateral ridge on the caudal peduncle
usually composed of scutes
provides stability and support to the
caudal fin