Ichthyology uses several terms that are unique to the science.

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
• Ankylosed: grown firmly together
• Anterior: relating to the front portion
• Antrose: turned forward
• Approximate: placed close together
• Asperity: roughness of surface
• Asymetrical: 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
• 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
• 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: rough-edged
• Cycloid: smooth-edged

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
• 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

• 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 air contained in water
• Glossohyal: the tongue bone
• Gonopodium: a modification of the anal fin of males of certain live-bearing species (i.e. family Poeciliidae), that 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
• 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
• 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

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
• Opercule, 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
• 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 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
• Symphysis: point of junction of the two sides of the jaw
• Symmetrical: similarly arranged on both sides
• Swimbladder: a sac filled with gas, lying beneath the backbone

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)