# Glossary of ichthyology

This glossary of ichthyology is a list of definitions of terms and concepts used in ichthyology, the study of fishes.
* A
* B
* C
* D
* E
* F
* G
* H
* I
* J
* K
* L
* M
* N
* O
* P
* Q
* R
* S
* T
* U
* V
* W
* X
* Y
* Z
* See also
* References
* External links

## A
### abdomen

    Belly.

### abdominal

    Pertaining to the belly.

### actinosts

    A series of bones at the base of the pectoral rays.

### acuminate

    Tapering gradually to a point.

### acute

    Sharp, pointed.

### adipose fin

    A small fleshy fin which lacks fin rays.

### adnate

    Joined together.

### adpressed

    Pressed against the body.

### anal fin

    The fin on the median line behind the vent.

### anal fin origin

    The most anterior point of the anal fin base.

### andropodium

    A modification of the anal fin of males of certain live-bearing species in the family Goodeidae. It is used to transfer reproductive products to the female during mating.

### ankylosed

    Grown firmly together.

### anterior

    Relating to the front portion.

### antrose

    Turned forward.

### approximate

    Placed close together.

### asperity

    Roughness of surface.

### asymmetrical

    Without symmetry.

### attenuate

    Tapering to a point, usually in reference to a tail.

### axillary

    Pertaining to the axilla or upper angle of the pectoral fin.

### axillary process

    An enlarged, pointed scale projecting from the insertion of the pectoral or pelvic fin.

## B
### barbel

    An elongated fleshy projection, usually about the head.

### basal

    At or pertaining to the base.

### base

    The part of a projection (commonly a fin) which is connected to the body.

### bathypelagic

    Living at a depth between 1000 m and 4000 m, but well off the bottom.

### benthic

    Bottom-dwelling, living on the sea bed.

### benthopelagic

    Pertaining to fishes that swim just above the seabed at depths below about 200 m (the edge of the continental shelf).

### bicuspid

    Having two cusps or points.

### bifid

    Cleft in two.

### bifurcate

    Forked, or divided into two parts or branches.

### branchial

    Pertaining to the gills.

### branchial aperture

    The gill opening.

### branchiostegal membrane

    The membrane connecting the branchiostegal rays and enclosing the gill chamber ventrally.

### branchiostegals, branchiostegal ray(s)

    Bony rays supporting the gill membranes behind the lower jaw.

### bristle

    A stiff hair-like projection.

### buckler

    A bony shield.

### bycatch

    Species other than the target species that are caught incidentally in a trawl.

## C
### caniniform

    Shaped like a canine tooth, conical in form.

### carapace

    A horny or bony covering encasing the body.

### cardiform

    Small set conical outgrowths in a close set patch or band; usually refers to a band of small, close-set, conical teeth.

### carinate

    Keeled, having a ridge along the middle line.

### caruncle

    A fleshy outgrowth.

### caudal

    Pertaining to the tail.

### caudal fin

    The tail fin.

### caudal peduncle

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

### ciliated

    Fringed with eyelash-like projections.

### cirri

    Small, thin appendages, often subdivided into branches.

### cirrus

    Singular of cirri.

### claspers

    The external reproductive organs of male sharks, rays, and chimaeras.

### coalesced

    Grown together.

### compressed

    Flattened laterally.

### confluent

    Joined together.

### conical

    Cone-shaped, with a cylindrical base and a pointed tip.

### corselet

    A scaly covering behind the pectorals of some fishes.

### countershading

    Body colouration which is dark above and lighter below.

### crenulate

    Having the edge slightly scalloped.

### cutaneous

    Pertaining to the skin.

### ctenoid scale

    A rough-edged scale.

### cycloid scale

    A smooth-edged scale.

## D
### deciduous

    Temporary, falling off.

### demersal

    Living on or near the sea bed.

### dendritic

    Resembling a tree or shrub.

### denature

    The "unfolding" of a protein resulting in a lessening of its biological properties. In the case of some fish toxins, denaturing with hot water can lessen painful symptoms.

### dentate

    Having tooth-like projections.

### denticle, denticulate

    A little tooth, having an edge with small projecting teeth, the placoid scales of cartilaginous fishes.

### depressed

    Flattened from top to bottom.

### dermal

    Pertaining to the skin.

### dewlap

    A fold of loose skin.

### disc

    The flattened head and body of various fishes such as stingrays, which also commonly includes the pectoral and ventral fins.

### distal

    Remote from the point of attachment.

### dorsal

    Pertaining to the back.

### dorsum

    The upper (dorsal) surface of the head or body.

### dorsal fin

    The fin on a fish's back.

### dorsal fin origin

    The most anterior point of the dorsal fin base.

## E
### elasmobranchs

    The cartilaginous fishes: sharks, rays, and allies.

### electrocyte

    A type of cell that generates electricity.

### elongate

    Extended, drawn out.

### emarginate

    Having the margin slightly hollowed.

### endemic

    Restricted to a particular region, for example endemic to Australia.

### entire

    Having a smooth margin.

### epibenthic

    Referring to organisms living on the bottom surface.

### epipelagic

    Referring to organisms living in the region between the surface and 200 m depth.

### erectile

    Capable of being raised or erected, often referring to spines.

### esca

    The lure or "bait" on the end of the illicium of some anglerfishes and relatives.

### estuarine

    Living in estuaries.

## F
### falcate

    Scythe-shaped, long, narrow, and curved.

### falciform

    Curved like a scythe.

### filament

    A slender or thread-like structure.

### filiform

    Thread-like.

### fimbriate

    Fringed at the margin.

### finfold

    Embryonic tissue which develops into a fin.

### finlet

    A small fin, positioned behind the dorsal or anal fins, that is supported by a ray or rays.

### fluviatile

    Living in rivers.

### free rear tips (of fins)

    The posterior tip of the fin that is closest to the most posterior point of the fin base.

### frontal ridge

    A ridge running along the top of the head along the midline.

### furcate

    Forked.

### fusiform

    Tapering towards both ends.

## G
### ganoid scales

    Armor-like scales coated with ganoin found in gars and bichirs.

### genital papilla

    A small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla.

### gill arches

    The bony arches to which the gills are attached.

### gill cover

    A bony flap that covers the gills; another name for the operculum.

### gill filaments

    A series of projections along the posterior edge of the gill arch, the site of gas exchange.

### gill membranes

    Membranes covering the gill openings, attached to the branchiostegals.

### gill opening

    The opening behind each operculum, leading to the gills.

### gill rakers

    A series of appendages along the anterior edges of the gill arches.

### gills, branchiae

    Organs for breathing the oxygen contained in water, and for excreting carbon dioxide from the blood.

### glossohyal

    The tongue bone.

### gonopodium

    A modification of the anal fin of males of certain live-bearing species in the families Anablepidae and Poeciliidae. It is used to transfer reproductive products to the female during mating.

### gravid

    Sexually ripe.

### gular region

    Pertaining to the region behind the chin and between the sides of the lower jaw.

## H
### head length

    The distance from the tip of the snout (or upper lip) to the most posterior point of the opercular margin.

### heterocercal

    (of a fin) Not symmetric, e.g. in sharks.

### homocercal

    (of a fin) Symmetric.

### homology

    Similarity of features based on common evolutionary descent.

### hyperostosis

    A condition resulting in enlargement of areas of bone.

### hyaline

    Translucent or transparent.

### hypural joint

    The joint between the caudal fin and the last of the vertebrae.

### hypural plate

    The flattened bony plate at the posterior end of the vertebral column, formed from parts of the posterior vertebrae.

## I
### ichthyoplankton

    The eggs and larvae of fish.

### illicium

    A "fishing rod-like" appendage on the head, usually a modified dorsal fin spine, used particularly in anglerfishes.

### imbricate

    Overlapping, like the shingles on a roof.

### incised

    Having a notched margin (often referring to fin membranes).

### incisors

    The front or cutting teeth.

### inferior

    Pertaining to the lower side (usually of the head).

### interdorsal

    Between the dorsal fins.

### interorbital

    The space between the orbits.

### intromittent organ

    A structure to facilitate sperm transfer in some internally fertilizing species.

### iris lappet

    A fleshy flap or lobe-like structure in the eye, short and rounded, simple or multiply branched.

### isthmus

    The fleshy projection of the body separating the gill openings.

## J
### jugular

    Pertaining to the throat.

### juxtaposed

    (of two or more objects) Placed near each other.

## K
### kidneys

    Organs involved in excretion and regulation of water balance.

## L
### lanceolate

    Spear-shaped; gradually tapering toward the extremity.

### labial

    Pertaining to the lips.

### labial furrows

    Shallow grooves around the lips.

### labial papillae

    Small fleshy projections around the lips.

### lateral

    At or toward the side.

### lateral line

    A series of muciferous tubes forming a raised line along the side of the body.

### leptocephalic

    Tallness and narrowness of the skull. In fish, the term usually refers to an "elongate highly compressed transparent, ribbon-like larval stage".

### liver

    A digestive and storage organ.

### longitudinal series (scales)

    The number of scale rows above the lateral line from the first pored lateral line scale to the caudal fin base.

### lunate

    Shaped like a crescent moon, with long upper and lower lobes.

## M
### maxilla, maxillary

    The upper jaw, or pertaining thereto.

### maxillae, maxillaries

    The hindmost bones of the upper jaw; preceded by the premaxillaries.

### median, medially

    Pertaining to the middle.

### median fins

    Fins located on the median line of the fish; the dorsal, anal and caudal fins.

### mediolateral

    Between the middle and the sides.

### melanophore

    A cell (chromatophore) containing melanin or other black pigment.

### mesocoracoid

    A bone of the pectoral arch or shoulder girdle.

### mesopelagic

    Refers to the region of the open ocean between 200 m and 1000 m in depth.

### mesopelagic fishes

    Fishes that live in the mesopelagic zone.

### midwater

    The middle stratum of water, well below the surface and well above the seabed. See also mesopelagic.

### midwater fishes

    Fishes that live in the midwater.

### molars

    Blunt and rounded grinding teeth.

### morphology

    Form and structure of an organism.

### muciferous

    Producing or containing mucus or slime.

### myotomes

    Blocks of lateral trunk muscles.

### myomeres

    Blocks of muscle corresponding to number of vertebrae, easily seen in larval fishes and used for identifying specimens.

## N
### nape

    Upper surface of the body behind the head and before the dorsal fin.

### nasal

    Pertaining to the nostrils.

### nasoral

    Between the nostrils and mouth.

### nictitating membrane

    An inner eyelid.

### notochord

    A rudimentary of embryonic spinal column.

### nuchal

    Pertaining to the nape.

## O
### obsolete

    Faintly marked; scarcely evident.

### obtuse

    Blunt.

### occipital

    Pertaining to the posterior part of the skull.

### ocellus

    An eye-like spot.

### ocular

    Pertaining to the eye.

### odontode

    A dermal tooth.

### oesophagus

    The gullet.

### opercle

    The large bone which forms the upper posterior part of the operculum.

### operculum

    The bony flap that covers the gills.

### opercular

    Pertaining to the operculum.

### opercular spine

    A spine projecting from the operculum.

### orbit

    The eye socket.

### origin

    The most anterior point of a fin base.

### osseous

    Bony.

### ovate

    Egg-shaped.

## P
### palate

    The roof of the mouth.

### palatines

    The set of bones on each side of the palate.

### papilla (papillae)

    A small fleshy projection(s).

### papillose

    Covered with papillae.

### pectoral

    Pertaining to the breast.

### pectoral fins

    The anterior or uppermost of the paired fins, which correspond to the anterior limbs of the higher vertebrates.

### pectoral girdle

    The bones to which the pectoral fin is attached.

### peduncle

    Usually referred to as the caudal peduncle, the region of the body between the end of the anal fin and the base of the caudal fin.

### pelagic

    Living on or in the open seas.

### pelvic girdle

    The bones to which the ventral fins are attached.

### pelvic fins

    Paired fins behind or below the pectoral fins.

### pharyngeal bones

    Bones behind the gills in the oesophagus or gullet.

### pharyngeal teeth

    Teeth within the pharynx.

### pharynx

    The back part of the throat, into which the gill slits open.

### photophore

    A circular light-producing organ on the surface of a fish.

### placoid scales

    Teeth-like scales found in sharks and rays.

### posterior

    Towards the hind end of the fish.

### postorbital

    Behind the eye.

### precaudal

    Anterior to the tail portion.

### premaxillaries

    Two bones forming the front portion of the upper jaw.

### preocular spine

    A spine positioned above and in front of the eye.

### preopercle, preoperculum

    The bone between the cheek and the gill cover.

### preopercular spine

    A spine projecting from the preopercule (see preopercle).

### preorbital

    The area under and in front of the eyes.

### protractile

    Capable of extending forward.

### protrusible

    Capable of extending forward, often referring to the jaws of fishes.

### proximal

    Nearest.

### pseudobranchiae

    Small gills developed on the inner side of the gill cover.

### pseudoclasper

    Stiff, ossified lobes or prongs in the tip of the intromittent organ.

### pterygiophore

    An internal cartilage or bone that supports a median fin ray or spine.

### pyloric caecae

    Finger-like pouches connected with the alimentary canal (the gut).

## R
### ramus

    One branch or one half of the jaw.

### ray

    A jointed, segmented rod which supports a fin.

### redd

    Spawning nest made by some fishes.

### retrose

    Turned backward.

### rostrum

    A projecting snout or beak.

### rugose

    Rough.

## S
### scalation

    The pattern/arrangement/presence of scales.

### scute

    Any external horny or bony plate.

### serrate

    Notched like a saw.

### setae

    Bristles or hairs.

### soft dorsal

    The posterior part of the dorsal fin which is composed of jointed rays.

### spatulate

    Shovel-like; having a broad, flat, and rounded shape.

### spine

    A sharp projecting point; an unjointed support in the anterior portions of the dorsal and anal fins.

### spinous, spiniform, spinate

    Spine-like or composed of spines.

### spinous dorsal

    The anterior part of the dorsal fin supported by spines.

### spiracles

    Respiratory openings behind the eyes in sharks and rays.

### standard length (SL)

    The length of a fish measured from the tip of the snout to the posterior extremity of the hypurals, the expanded bones at the end of the backbone that support the caudal fin.

### submarginal

    Almost at the edge.

### suborbital

    Below the eye.

### superior

    Above or on the upper surface.

### supracleithrum

    The bone forming a connection between the back of the skull and the pectoral girdle.

### supralateral

    Above the side.

### supramaxillary

    A supplemental bone lying along the upper edge of the maxillary.

### supraocular

    Positioned above the eye.

### supraorbital

    Above the eye.

### supraorbital tentacle

    A flap or filament of skin positioned above the eye.

### suprascapular

    A bone uniting the shoulder girdle with the skull.

### suture

    The line of union of two bones or plates.

### swimbladder

    A sac filled with gas, lying beneath the backbone.

### symphysis

    The point of junction of the two sides of the jaw.

### symmetrical

    Similarly arranged on both sides.

## T
### teleost

    A member of Teleostei, an infraclass containing most of the bony fishes.

### terminal

    At the end.

### tessellated

    Marked with little checks or squares, like tiles.

### Tholichthys

    A larval stage of butterflyfish and scats in which the larva is armoured with large bony plates which extend onto the body from the head, the head also being enclosed in bony armour which is frequently silvery in colour. The tholichthys armour plates are lost as the larva metamorphoses into the juvenile stage.

### thoracic

    Pertaining to the chest.

### thorax

    The chest region, just behind the head.

### total length

    The length from the tip of the snout to the tip of the tail.

### transverse

    Crosswise.

### trilobate

    Having three lobes.

### tricuspid

    Having three cusps or points.

### truncate

    Terminating abruptly, as if cut off square.

### trunk

    The region of a fish between the head and tail, or the last gill slit and vent.

### tubercle

    A small, usually hard excrescence or lump.

### tubiform, tubuliform

    Resembling a tube.

### type locality

    The location from which the type specimen was collected.

## U
### undulated

    Waved.

### urogenital papilla

    A papilla through which the urinary waste and gametes leave the body.

## V
### vent

    The external opening of the alimentary canal, the anus.

### ventral

    Pertaining to the abdominal or lower surface.

### ventral fins

    Paired fins behind or below the pectoral fins.

### vertical fins

    Fins on the median line of the body; the dorsal, anal, and caudal fins.

### vestigial

    Reduced or very poorly developed.

### villiform teeth

    Small, slender teeth forming velvety bands.

### vomer

    A bone forming the front part of the roof of the mouth.

### vomerine teeth

    Teeth on the vomer.

## W
### Weberian apparatus

    An adaptation found in Ostariophysi to improve hearing; includes the Weberian ossicles.