Fish Anatomy

Nearly all fish have a streamlined body plan, which is divided into head, trunk, and tail, although the dividing points are not always externally visible.

The head includes the snout, from the eye to the forwardmost point of the upper jaw, the operculum or gill cover, (absent in sharks) and the cheek, which extends from eye to preopercle. The lower jaw defines a chin. The head may have several fleshy structures known as barbels, which may be very long and resemble whiskers. Many fish species also have a variety of protrusions or spines on the head. The nostrils or nares of almost all fishes do not connect to the oral cavity, but are pits of varying shape and depth.

The outer body of many fish is covered with scales. Some species are covered instead by scutes. Others have no outer covering on the skin; these are called naked fish. Most fish are covered in a protective layer of slime (mucus).

The lateral line is a sense organ used to detect movement and vibration in the surrounding water. It consists of a line of receptors running along each side of the fish.

The caudal peduncle is the narrow part of the fish's body to which the caudal or tail fin is attached. The hypural joint is the joint between the caudal fin and the last of the vertebrae.

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Eye	sight organ of a fish.
Operculum	pair of rigid plates covering and protecting the gills of a fish.
Lateral line	central line dividing a fish lengthwise.
Spiny ray	spine travelling the length of a fin.
Dorsal fin	locomotive limb situated on the back of a fish.
Caudal fin	locomotive limb situated at the end of a fish.
Anal fin	locomotive limb situated behind the anus of a fish.
Pelvic fin	locomotive limb situated beneath the pelvic girdle of a fish.
Scale	each of the small hard plates covering a fish.
Pectoral fin	locomotive limb situated at the chest of a fish.
Mandible	lower jaw.
Mouth	entrance of the digestive tract.
Maxillary	bone forming the upper jaw

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Brain	seat of the mental faculties of a fish.
Esophagus	part of the digestive tract connecting the mouth to the stomach.
Dorsal aorta	vessel in the back that carries blood from the heart to the organs.
Stomach	part of the digestive tract between the esophagus and the intestine.
Air bladder	pocket in which urine collects.
Spinal cord	part of the nervous system that connects the brain to all other parts of a fish.
Kidney	blood-purifying organ.
Urinary orifice	opening for eliminating urine.
Genital Orifice	opening related to the genital organs.
Anus	end of the digestive tract.
Gonad	hormone-secreting sexual gland of a fish.
Intestine	last part of the digestive tract.
Pyloric cecum	cul-de-sac related to the intestine.
Gall bladder	small sac containing the bile.
Liver	bile-producing digestive gland.
Heart	blood-pumping organ.
Gills	respiratory organ of a fish.
Tooth	hard organ of a fish used to shred food.
Eye	sight organ of a fish.
Olfactory bulb	bulging part of the smell organ of smell of a fish.

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Opercular	pair of bony plates covering the gill opening.
Ray of the anterior dorsal fin	each of the small bones forming the front fin on the back of a fish.
Radial cartilage	elastic substance of the radius.
Ray of the posterior dorsal fin	each of the small bones forming the rear fin on the back of a fish.
Neural spine	spine containing part of the nervous system.
Vertebra	each of the bones forming the neural spine of a fish.
Hypural	bone to which are attached the spiny rays of the caudal fin of a fish.
Caudal fin ray	each of the small bones forming the tail fin of a fish.
Anal fin ray	each of the small bones forming the fin behind the anus of a fish.
Radial cartilage	elastic substance of the radius.
Rib	each of the bones forming the thoracic cage.
Pelvic fin ray	each of the bones forming the fin beneath the pelvic girdle.
Pectoral fin ray	each of the bones forming the chest fin.
Pelvic girdle	set of bones forming the pelvis.
Clavicle	shoulder bone.
Lower jaw	mandible.
Upper jaw	upper part of the mouth.
Orbit	cavity of the skull that contains the eye.
Skull	bony case of the brain of a fish.

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