Glossary of ichthyology

Ichthyology uses several terms that are unique to the science.

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.

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