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.
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.

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