Glossary of Fish Terms

 

Term Definition
abbreviate heterocercal tail

Tail which the upper and lower lobes of tail fin are somewhat symmetrical and the vertebrae (backbone) flexes upward and partially extends onto tail fin. Found in gars. Intermediate between heterocercal and homocercal tails.

abdomen

Belly

adipose fin

A small fleshy fin, lacking rays or spines, located on the midline of the dorsal surface between the dorsal fin and caudal fin.

anal fin

A single, unpaired fin located along the midline of ventral surface between the anus and caudal fin. The anal fin may have spines and rays or just rays.

anterior

To the front.

axil

The inner angle at which the pelvic or pectoral fin is joined to the body.

auxiliary process

A bony splint extending from the upper or anterior base of a pelvic or pectoral fin.

auxiliary scales

Scales of small sizes superimposed on or along margin of larger scales.

barb

A backward pointing projection, as on some spines.

barbel

A fleshy and flexible process, usually covered with taste buds, found near the mouth.

base

The part of a fin that is attached to the body.

biconcave tail

Outer and inner fin rays longer giving a double concave shape; same as double emarginate.

bi-lobed tail

Upper and lower lobes are rounded, middle rays slightly shorter, no deep V shape in center.

blotch

Pigmented spot with an indistinct outline or shape.

body depth

The greatest straight-line height or depth of the body, from the dorsal to the ventral surface.

branched

Split into 2 or more extensions at the tip, as in some fin rays.

branchial cavity

The area contains the gills, often also includes the throat.

branchiostegal membranes

Flexible membranes connecting the branchiostegal rays to each other and to the opercle. The branchiostegal membranes provide the seal that allows the movement of the gill cover and branchiostegal rays to pump water over the gills.

branchiostegal rays

Thin bones located just posterior and ventral to the gill covers that support the gill membranes..

canine

Long, pointed, conical tooth.

caudal base

The base of the caudal fin (tail) where the vertebral column ends, which can be seen as a crease in the skin when the tail is flexed from side to side.

caudal fin

The tail fin.

caudal peduncle

The portion of the body between the posterior end of the anal fin base and the caudal base.

cheek

The portion of the head between the eye and the posterior edge of the preopercle.

chromatophore

A cell containing pigment.

cirrus (pl. cirri)

A small fleshy or hair-like extension.

claspers

The external reproductive organs of male sharks and rays.

concave

Curving inward.

continuous tail

No separate tail fin, tail rays are continuous with dorsal and anal fins, as in some eels.

convex

Curving outward.

cusp

A pointed or rounded projection on the chewing surface of a tooth.

disk (disc)

Something thin, flat and circular; the body of a ray.

dorsal

Pertaining to the top (back) of the fish.

dorsal fin

An unpaired fin located along the midline of the dorsal surface. It may have both spines and rays or just rays and consist of a single lobe, two lobes that are joined or separate, or a series of free spines and a lobe with rays.

dorsoventrally flattened

A body or head shape in which the width is clearly greater than the depth and the fish looks as if it has been flattened from above.

double emarginate tail

Upper and lower lobes emarginate (concave), either with a notch between the lobes or rounded in the center (inner and outer rays longer); same as biconcave.

emarginate tail

Slightly curved inward (concave), center rays slightly shorter than upper or lower rays.

falcate

A fin shape, in the dorsal fin or anal fin, in which the anterior few rays are noticeably and somewhat abruptly longer than subsequent rays, giving the edge of the fin a strongly curved (sickle-shaped) or concave profile

falcate tail

Tail fin shaped like a sickle, deeply concave, with the middle rays much shorter than the anterior or posterior rays.

fin

A fold of skin supported by bony or cartilaginous rays or spines, used for locomotion, balance, steering, display, etc.

fin lobe

The extended or projected portion of fins, usually composed of elongated fin rays.

finlet

A small, isolated fin, usually found posterior to the dorsal or anal fin.

FL

Fork length

fleshy tail

No tail fin, just fleshy knob, but not whip-like.

fork length

The straight-line distance from the most forward part of the head (or forward most tip of the lower jaw in billfishes) to the rear center edge or the innermost spot of the concave part of the tail.

forked tail

Deep V-shaped center.

gill

A filamentous respiratory organ which removes oxygen from water.

gill arch

Bony or cartilaginous arch that support the gills, arranged in overlapping layers, and covered by the gill covers.

gill cover

The flat bony plates that cover the branchial cavity and gills, consisting of the preopercle, interopercle, subopercle, and opercle; see operculum.

gill opening

See gill slit.

gill rakers

Knobby or comb-like cartilaginous filaments extending anteriorly and inward from the gill arches. Used to sieve small food items from water passing over the gills.

gill slit

Slit-like openings on the bottom (rays) or sides of fishes that lead to the gills. Most fishes only have one on each side behind the head. Sharks and rays have multiple pairs of gill slits.

gular plate

A flat bone in the middle of lower jaw of certain fishes of ancient origin.

head length

The straight-line distance from the most forward part of the head to the posterior end of the operculum (gill cover).

heterocercal tail

Upper lobe of tail fin is much longer than lower lobe with vertebral column (backbone) flexing upward and extending into the upper lobe of the fin, common in some sharks.

homocercal tail

Upper and lower lobes of tail fin approximately symmetrical and the vertebral column ends at or near the middle of the tail fin base, not extending onto the fin. Homocercal includes all tail shapes (except in special cases) in which a tail fin is present

inferior mouth

A mouth located on the ventral surface of the head and oriented downwards.

interdorsal ridge

A ridge on the back of some sharks, running between the 2 dorsal fins.

interopercle

The bony plate that lies beneath the lower edge of the preopercle. One of the 4 plates that make up the gill cover (operculum).

interpelvic process

A fleshy process between the inner edges of the pelvic fins, in mackerels and tunas

isthmus

The fleshy external area between the 2 gill cavities (throat or anterior breast area).

jaw

An opposable, articulated structure at the entrance of the mouth, used for grasping and manipulating food. The outer parts of the jaws in most fishes include the lower jaw (mandible) and the upper jaw (premaxillary, maxillary and supramaxillary).

jugostegalia

Basket-like structure of over-lapping free branchiostegal rays used as support for the extended branchial region in some eels.

keel

A relatively narrow and sharp ridge-like area of the ventral or dorsal surfaces or the sides of the caudal peduncle.

labial folds

In some sharks, a U-shaped fold found at the corners of the mouth.

lanceolate tail

Middle rays longer than upper or lower rays and tapering to a point.

lateral

The sides of a body.

lateral line

A sensory canal running along each side of many species having numerous openings or pores. The number of scales along the side with these pores (one pore per scale) between the posterior end of the opercle and the caudal base is the lateral line scale co

laterally compressed

A body shape in which the body depth is more than the body width.

left-eyed

A flatfish in which the eyes are on the left side of the body, determined by the position of the eyes to the mouth.

lunate tail

Crescent-moon shaped.

mandible

The lower jaw of some fishes.

maxillary

One of the bones of the upper jaw of fishes.

melanophore

A cell of containing melanin (a dark pigment) found on the skin and fins.

meristic

A countable trait used to describe a particular species of fish, such as fin spines and rays or lateral line scales.

mottling

Areas of color with no particular shape or pattern.

nape

The area on the back between the head and the dorsal fin.

oblique

Angled, either upward or downward, usually refers to mouths, stripes or lines.

occipital pit

A cavity or pit in the upper skull, behind the eyes; serves some sensory function.

ocular side

In flatfish, the side (top) that the eyes are on.

opercle

The largest and posterior-most of the bony plates that make up the gill covers.

operculum

A bony plate that covers the gills

origin (of a fin)

The anterior-most point where the fin connects with the body.

ovate

Oval in appearance, usually longer than wide or vise versa.

palatine teeth

Patches of small teeth on that are found on each side of the roof of the mouth.

pectoral fins

Paired fins located on the side of a fish just posterior to the gill covers.

pelvic fins

Paired fins located on the ventral (bottom) surface either just anterior to the anus, underneath the pectoral fins, or just posterior to the throat.

photophore

A light-producing organ or spot.

pointed tail

Middle rays longer than upper or lower rays and tapering to a point.

posterior

To the rear.

precaudal groove

A groove or notch on the upper area of the caudal base. Also called precaudal pit.

predorsal

The area anterior to the dorsal fin.

premaxillary

The anterior-most bone in the upper jaw of fishes.

premaxillary groove

A groove on the head from between the eyes to the edge of the upper lip.

preopercle

The anterior-most of the 4 bony plates that make up the gill cover (operculum).

prickle

A small spiny projection.

protractile

Refers to lips that can be extended or thrust out from the jaw and that are not rigidly connected to the upper jaw.

ray

A segmented flexible support element of the fins, often branched at the tip; a cartilaginous fish that is flatten dorsoventrally and usually has a whip-like tail.

rhomboidal

Rhomboid or diamond-shaped.

right-eyed

A flatfish in which the eyes are on the right side of the body, determined by the position of the eyes to the mouth.

rostrum

A hardened snout that usually extends past the face.

rounded tail

Middle rays longer than upper or lower rays and posterior edge is rounded.

rudimentary

Small, undeveloped, primitive.

saddle

Blotch of dark pigment extending from the sides over the dorsal surface

scute

A large hard scale, sometimes keeled, usually found on the sides along the lateral line.

serrated

Saw-toothed.

shoulder

In fish, the area around the upper end of the opercle.

SL

Standard length

snout

The area from the tip of the head to the front of the eye.

snout length

The straight-line distance from the most forward part of the head to the front of the eye.

soft dorsal fin

A dorsal fin or a portion of a dorsal fin that has no spines, only rays.

spine

An un-segmented, rigid, support element of the fins, pointed at the tip, never branched; a rigid, pointed, usually flat bony process extending from the posterior edge of the opercles; a hard, sharp, serrated process on the base of the tail of stingrays.

spiracle

In rays and some sharks, an opening on the head behind the eye through which water is drawn and passed over gills; aids the fish in breathing even when it is lying on the ocean bottom or buried in the sand.

S-shaped tail

Usually upper rays longer and pointed, middle rays shorter, and lower rays longer and curve shaped, giving an S shape; concave upper half, convex lower half.

standard length

The straight-line distance from the most forward part of the head to the end of the vertebral column (i.e. the caudal base) which can be seen as a crease in the skin when the tail is flexed from side to side.

subopercle

The bony plate that lies posterior to the interopercle and below the opercle. One of the 4 bony plates that make up the gill cover (operculum).

suborbital stay

A bony ridge from beneath the eye to the preopercle, usually has spines.

subterminal mouth

A mouth oriented and opening somewhat ventrally in which the upper jaw and snout clearly extend beyond the lower jaw.

superior mouth

A mouth where the lower jaw distinctly projects beyond the upper jaw and mouth opens upward.

supramaxillary

A small bone on the posterior end of the upper jaw of some fishes.

supraterminal mouth

A mouth where the lower jaw slightly projects beyond the upper jaw and mouth tends to open upward.

swimbladder

A gas-filled sac in the body cavity of most fishes, used as an aid to buoyancy.

terminal mouth

A mouth opening at the anterior tip of the head in which the upper and lower jaws are approximately the same length with neither one extending beyond the other.

throat

The area of the ventral surface below the branchial cavity and just anterior to the breast that includes the isthmus.

TL

Total length

total length

The straight-line distance from the most forward point of the head to the posterior tip of the caudal fin when compressed.

truncate tail

A more or less vertical edge.

tubercle

A calcified and hard protuberance.

tympanum

An area of enlarged scales behind the gill opening that can be vibrated to produce sound, in triggerfishes and filefishes

ventral

Pertaining to the underside or bottom of the fish.

vomerine teeth

Teeth found along the midline of the roof of the mouth.

whip-like tail

Rounded in diameter, long and thin, no fin rays.