External Anatomy of Fish

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External Anatomy of Fish
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The Head
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Mouth Shape/ Position

• Superior Mouth
• Also known as an undershot or upturned mouth
• Eats food above the fish
• May eat at the waters 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

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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

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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

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The Body
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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

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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.

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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.

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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

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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 fishs body fluids so that they
  are not diluted by the watery surroundings
• makes the fish slippery when predators try to
  grab hold

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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.

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Peduncle

• The edge of the tail fin that lies on the end or
  outside of the caudal fin

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Types of Fins
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Fins

• used for movement, stability, nest-building,
  spawning, and as tactile organs
• can be single or paired

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Tail fin

• Also known as the caudal fin
• Used for propulsion
• Large, elongated caudal fins are often used to
  attract mates.

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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

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• 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

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• 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

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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

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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

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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

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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

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Adipose fin

• is a tiny fin found between the dorsal and caudal
  fins on some fish
• a soft, fleshy fin

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Finlets

• small fins
• generally behind the dorsal and anal fins
• they are rayless and non-retractable

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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