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, nest-building, 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