Glossary of ichthyology

Updated on Sep 30, 2024

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Ichthyology uses several terms that are unique to the science.

A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
R
S
T
U
V
W
References

Contents: 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

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: pertaining to the base, at 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 close set small 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 (see above)

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: rough-edged scale

Cycloid scale: 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: with 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: cartilaginous fishes - sharks, rays and allies

Electrocyte: a cell that generates electricity

Elongate: extended, drawn out

Emarginate: with the margin slightly hollowed

Endemic: restricted to a particular region, for example endemic to Australia

Entire: with 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: or bony flap that covers the gills, 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: 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 fin: not symmetric (sharks)

Homocercal 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: fish eggs and larvae

Illicium: a "fishing rod-like" appendage on the head, usually a modified dorsal fin spine

Imbricate: overlapping, like the shingles on a roof

Incised: with 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 fertilizating 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: placed near together

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 usually refers to "elongate highly compressed transparent, ribbon-like larval stage" (source FishBase glossary)

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: spine projecting from the operculum (view the fish figure)

Orbit: the eye socket

Origin: the most anterior point of a fin base

Osseus: bony

Ovate: egg-shaped

P

Palate: the roof of the mouth

Palatines: the 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: spine positioned above and in front of the eye

Preopercle, preoperculum: the bone between the cheek and the gill cover

Preopercular spine: spine projecting from the preopercule (see preopercle) (view the fish figure)

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

Retrose: turned backward

Rostrum: a projecting snout or beak

Rugose: rough

S

Scalation: pertains to 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: 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

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: with three lobes

Tricuspid: with 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 (see above)

W

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

References

Glossary of ichthyology Wikipedia

(Text) CC BY-SA