Terms and Definitions
by Max Arno
modified from Eschmeyer et al 19__


Abdomen The belly or lower surface of a fish, especially between the pelvic fins and the anus.
Abdominal Refers to the location of the pelvic fins on the belly
Anadromous Moving from the sea into fresh water to spawn, as in salmons and shads.
Anal fin A median fin located on the undersurface, usually just behind the anus; rarely notched or subdivided.
Anterior Front; located toward the front.
Anus The rear external opening of the digestive tract; the vent
Axil The inner base of a pectoral fin; the "armpit."
Bar A vertical band of color. (Compare with stripe)
Barbel An elongate projection (usually fleshy and whiskerlike) Found on the lower surface of the head or near the mouth in some fishes.
Base of Fin The part of a fin that is attached to the body.
Benthic Living on or near the bottom or in close association with the bottom.
Branchiostegal rays Ray like bony supports for the gill membranes, located at the throat.
Breast The chest area; usually in front of the pelvic fins.
Canine A pointed, conical tooth, which is usually larger than the surrounding teeth.
Cartilaginous Made of cartilage. Cartilage is the translucent material that makes up the skeleton of young fishes, which persists in adults of some species (notably sharks and rays) but is largely converted to bone in most fishes.
Caudal fin A median fin at the rear of the body; the "tail fin."
Caudal peduncle - The narrower part of the body just before the caudal fin; usually refers to the part of a fish between the rear of the anal fin to the base of the caudle fin.
Cirrus - A small, thin flap of skin; a fleshy appendage that can be located anywhere on the fish (on the eyeball, on a nostril, on the top of the head, along the latrine line, ect.).
Compressed Flattened from side to side.
Concave Bowed or curved inward.
Continuous - Unbroken; usually refers to a dorsal fin in which the spinous part is joined to the soft-rayed part, with no gap or notch between the two.
Convex Bowed or curved outward.
Copepods A group of tiny crustaceans, some are free swimming; others are parasitic on fishes.
Crescent-shaped Shaped like a quarter moon; used to describe the shape of the caudal fin, or pigmented patches on a fish's body.
Ctenoid A type of scale; the rear (exposed) edge of each scale is toothed; making the scale rough to the touch.
Cycloid Another type of scale, with a smooth rear edge which makes the scale smooth to the touch.
Disk (1) The flat, nearly round body of skates and rays, formed by pectoral fins that are fully attached to the body (2) An adhesive (clinging) organ in some fishes
Dorsal above; on top.
Dorsal fin a median rayed fin on the back often notched or subdivided; sometimes fully divided into 2 separate fins.
Embedded Used to describe scales that are buried or wholly covered by skin
Eyespot An eyelike, pigmented spot; usually dark, bordered by a ring of pale pigment.
J Opercle: The thin bone forming most of the gill cover.
,/Orbit: The bony eye socket. Orbital: Related to the eye. (See also interorbital, suborbital.)
Filamentous Threadlike; usually refers to elongated fin rays or barbell.
Forked Usually applied to a caudal fin with a distinct upper and lower lobe, seperated by a deep notch.
Gas bladder An air sac found in many fishes, which is located under the spinal column, above the gut cavity; also called the swim bladder by some researchers.
Genital papilla A small, fleshy swelling or projection near the anus in some fishes; sometimes developed into a penis like structure.
Gills organs in fishes; including the highly vascularized filaments that are used to extract oxygen from the water.
Gill arch The bony support to which the gill filaments and gill rakers are attached.
Gill chamber The cavity where the gills are located.
Gill cover A bony flap that covers the outside of the gill chamber.
Gill openings The openings at the rear of the head, from the gill chamber to the outside (most fishes have 1 on each side); called gill slits in sharks and rays.
Gill rakers Bony, toothlike projections from the front edge of
the gill arch, opposite the gill filaments; often used as water
filters to trap food items between the gill arches.
Gill slits The slitlike gill openings (5 7 on each side) in sharks and rays.
Habitat The place where a fish (or other kind of animal) normally lives.
Head length The length as measured from the tip of the snout to
the rear edge of the gill cover

Vegetarian, feeding on plants; among fishes, those that feed on algae.

Hermaphrodite Having both male and female organs in one body.

Cut away or notched ( such as the fin membranes between the spines).

Incisors Front teeth that are flattened to form a cutting edge.
Intertidal Between high-water mark and low-water mark, also refers to fishes living in this area, especially tidepool fishes.
Isthmus A narrow extension of the throat between the gill chambers.
Jugular In the throat area; usually refers to location of the pelvic fins.
Juvenile of a species; usually a miniature version of the adult.
Labial groove A groove or furrow at the corner of the mouth in sharks.
Larva Newborn; the developmental stage of a fish before it becomes a juvenile.
Lateral Side; on the side.
Lateral line A row of porelike openings on head and body; usually applied to the series of pores or pored scales along the side of the fish's body.
Lunate Crescent shaped; usually refers to the shape of the caudal fin.
Maxillary A bone in the upper jaw, comprising most of the upper jaw or only the rear part of the upper jaw.
Median fin One of the unpaired fins located on the midline (on the median plane, which divides the body vertically into two halves) the dorsal, anal, and caudal fins.
Molar A flat topped tooth used for crushing food.
Naked Smooth or unsealed. Nictitating eyelid: A membrane of skin that can be extended over the eye in some sharks and bony fishes.
Nocturnal Active at night.
Nostril A nasal opening (fishes usually have 2 on each side).
Notched Indented; especially refers to a fin in which some rays (at the middle) are shorter
Ocellus An eyelike, pigmented spot; usually dark, bordered by a ring of pale pigment.
J Opercle: The thin bone forming most of the gill cover.
,/Orbit: The bony eye socket. Orbital: Related to the eye. (See also interorbital, suborbital.)
Oviparous Egg laying. The eggs develop into embryos after being laid by the female.
Ovoviviparous Another type of embryonic development, in which the fertilized eggs complete all or nearly all of their development inside the female's body before they hatch. (Compare with viviparous.)
Papilla A small fleshy knob or projection
Pelvic fin One of a pair of fins on the lower surface of the body, usually located below the pectoral fins.
Pore A tiny opening in the skin; usually involved with sensory perception in fishes.
Posterior Rear, behind toward the rear.
Preopercle A cheek bone, at the front of the gill cover (which often bears spines, as in sculpins).
Protrusible Refers to the mouth; having jaws that can be protruded (thrust forward and out).
Reticulate Color markings in a chainlike pattern or network.
Rostral Pertaining to the snout; a beaklike extension or plate at the tip of the snout.
Scute : A bony projection, often a modified scale.
Serrate Sawlike; usually refers to a sawtoothed edge.
Snout: The part of head in front of the eyes.
Soft dorsal fin A median fin on the back, composed entirely of
soft fin rays, or having one stiff spine at the front.
Soft ray A flexible, jointed (segmented) fin ray; often branched.
Spine (1) A bony projection usually on the head. (2) A single
hard, unbranched ray in a fin a spinous ray.
Spinous ray A hard spine (fin ray), with no segments or
Stripe A horizontal band of color. (Compare with bar.)
Suborbital : Below the eyes.
Subspecies A geographic subgroup within one species
Subtidal Just below the low water mark; also refers to fishes
living in this area.
Tail The area of the body behind the anus in most fishes (not just the tail fin).
Territorial Defending a home (such as a burrow or reef crevice) or a particular area.
Testis Male reproductive gland.
Thoracic : In the breast area (refers to pelvic fin location).
Truncate Having a sqaure cut rear edge (refers to the shape of the caudal fin).
Tubercles Small (often cone shaped) projections.
Vent The combined external opening of the digestive, urinary, and reproductive tubes.
Ventral On the lower surface; on the belly.
Vermiculations A color pattern of short, wavy (often wormlike) lines or spots.
Viviparous Giving birth to live young. The young are nourished by a placentalike structure in the mother before their birth. (Compare with ovoviviparous and oviparous.)
Vomerine Pertaining to the vomer usually a median bone in the front of the roof of the mouth; often used to describe location of teeth on this bone.
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