Fish Terminology

Abdomen

The belly or lower surface of a fish, especially between the pelvic fins and the anus

Adipose eyelid

Fatty, translucent tissue that partially covers the eyeball in some fishes

Adipose fin

A small fleshy fin w/ no rays or spines; located on the back (slightly anterior to caudal fin) in some fishes

Alar spines

A group of spines near the disk edge in some male skates

Anadromous

Moving from the sea into fresh water to spawn, as in salmon 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

Barbel

An elongate projection (usually fleshy & whisker like) 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

Bathypelagic

In the deep sea [deeper than about 1200ft (366m)]; refers to the habitat of deep sea fishes

Benthic

Living on or near the bottom of in close association w/ the bottom

Blind side

The light-colored underside, which lacks eyes, in flatfishes

Branchiostegal rays

Raylike 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 (sharks/rays), but is largely converted to bone in most fishes]

Caudal fin

A median fin at the rear of the body; “tail” fin

Caudal peduncle

The narrower part of the body just before the caudal fin; usually refers to the part of a fish btwn the rear of anal fin & the base of the caudal fin

Cirrus

A small, thin flap of slime; a fleshy appendage that can be located anywhere on the fish (e.g. on the eyeball, on a nostril, top of head, along the LL)

Clasper

A fleshy modified part of the pelvic fins in male sharks & their relatives (Skates/Rays); used in transfer of sperm

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, w/ no gap or notch btwn the two

Convex

Bowed or curved outward

Copepods

A group of tiny crustaceans. Some are free-swimming; others are parasitic on fishes

Corselet

A scaled area on the front of the body in certain tuna-like fishes

Crescent-shaped

Shaped like a quarter moon; used to describe shape of caudal fin or pigmented patches on a fish’s body

Crustaceans

A large class of arthropods, usually covered w/ a horny shell (e.g. shrimps, crabs)

Ctenoid

A type of scale; the rear (exposed) edge of each scale is toothed, making the scale rough to touch

Cusp

The main point of a tooth; used here in ref to shark teeth

Cusplet

A small projection on a tooth

Cycloid

Another type of scale, w/ a smooth rear edge; which makes the scale smooth to touch

Denticles

Small teeth; usually refers to prickles (modified scales) on some fishes, especially sharks & rays

Disk

(1) The flat, nearly round body of skates & rays, formed by pectoral fins that are fully attached to the body

(2) An adhesive (clinging) organ in some fishes, such as cling-fishes, snail fishes, & remoras

Dorsal

Above; on top

Dorsal Fin

A median, rayed fin on the back, often notched or subdivided; sometimes fully divided into 2 separate fins

Echinoderms

A group (phylum) of marine inverts, including sea stars & urchins

Embedded

Used to describe scales that are buried or wholly covered by skin

Epipelagic

At or near the surface; usually in the open ocean

Eyed side

In flatfishes, the dark-colored side, on which both eyes are located

Filamentous

Threadlike; usually refers to elongated fin rays or barbels

Finlet

A small rayed fin, usually in a series, and often following the main dorsal or anal fin (as in tunas/mackerels)

Forked

Usually applied to a caudal fin w/ a distinct upper & lower lobe, separated by a deep notch

Fusiform

Cigar-shaped; tapering at both ends (usually refers to body shape)

Gas bladder

An air sac found in many fishes, located under the spinal column above the gut cavity; also called the swim bladder

Genital papilla

A small, fleshy swelling or projection near the anus in some fishes; sometimes developed into a penis-like structure

Gills

Respiratory 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/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 btwn the gill arches

Gill slits

Slitlike gill openings in sharks/rays

Head length

Length as measured from the tip of the snout to the rear edge of the gill cover

Hermaphrodite

Having both male and female organs in one body

Heterocercal

A type of caudal fin in which the vertebral column extends into the upper lobe, which is usually larger

Incised

Cut away or notched (e.g. fin membranes btwn the spines)

Incisors

Front teeth that are flattened to form a cutting edge

Indented

Usually refers to the shape of the rear of the caudal fin; w/ a slight notch at the middle

Interorbital

Btwn the eyes

Intertidal

Btwn high-water mark & low-water mark; also refers to fishes living in this area, especially tidepool fishes

Isthmus

A narrow extension of the throat btwn the gill chambers

Jugular

In the throat area; usually refers to location of pelvic fins

Keel

A horizontal (shelflike) fleshy or bony ridge; often located at the base of the caudal fin

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 line

A row of porelike openings on head & body; usually applied to the series of pores or pored scales along the side of the fish’s body

Leptocephalus

A ribbonlike pelagic larva of eels & some primitive fish

Lunate

Crescent-shaped; e.g. caudal fin shape

Malar spines

A group of spines near the front of the disk in some male skates

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 midine (on the median plane, which divides the body vertically into two halves) e.g. Dorsal, anal, caudal fins

Molar

A flat-topped tooth used for crushing food

Naked

Smooth or unscaled

Nicitating eyelid

A membrane of skin that can be extended over the eye in some sharks & bony fishes

Notched

Indented; especially refers to a fin in which some rays (@ the middle) are shorter

Ocellus

An eyelike, pigmented spot; usually dark, bordered by a ring of pale pigment

Opercle

The thin bone forming most of the gill cover

Orbit

The bony eye socket

Orbital

Related to the eye (e.g. 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.

Papilla

A small fleshy knob or projection

Pectoral fin

One of a pair of fins (on each side) that are attached to the should girdle, posterior to head

Pelagic

Found in open water; in the water column, usually near the surface

Peritoneum

The membrane lining the abdominal cavity

Photophore

A dotlike light-producing organ.

Precaudal Pit

In sharks, a horizontal notch just in front of the caudal fin (which may be on the upper or lower part of the caudal peduncle)

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 & out)

Reticulate

Color markings in a chain like pattern or network

Rostral

Pertaining to the snout; a beak like extension or plate at the tip of the snout.

Scapular spine

A spine on the disk of some skates, on each side of midline, on back.

Scute

A bony projection, often a modified scale.

Serrate

Sawlike; usually refers to a sawtoothed edge

Soft dorsal fin

A media 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