Glossary of ichthyology

See also: Fisheries glossary

This glossary of ichthyology is a list of definitions of terms and concepts used in ichthyology, the study of fishes.^[1]

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 mucous 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.

References

1. Ruschenberger, William Samuel Waithman (1846). Elements of Herpetology, and of Ichthyology: Prepared for the Use of Schools and Colleges. Grigg & Elliot. pp. 129–145.

Further reading

• Moyle, Peter; Cech, Joseph (2004). Fishes: An Introduction to Ichthyology. Pearson Prentice Hall. ISBN 9780131008472.