Glossary of ichthyology

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

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.
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.