Glossary of fish terms

Updated

03/03/23
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This page lists many of the terms used throughout the site.

A

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
Adelphophagous	A mode of feeding where an embryo feeds on other embryos within the uterus of the female.
Adipose	Fatty. A term often used in reference to small rayless fins and to eyelids.
Adipose fin	a small fleshy fin which lacks fin rays. See adipose.
Adnate	joined together
Adpressed	pressed against the body
Aestivate	to be inactive during warm dry periods
Airbladder	see swimbladder
Alimentary canal	the passage through which food passes, starting at the mouth and ending at the anus
Anal	pertaining to the anus or anal fin
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
Anlage	Rudimentary form of an anatomical structure; primordium; a German word the plural of which is anlagen.
Anterior	relating to the front portion.
Antitropical	Found in temperate waters of both hemispheres but not in the tropics.
Antrose	turned forward
Anus	the external opening of the intestine, the vent
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

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
Body depth (BD)	For larvae: The vertical distance between body margins (exclusive of fins) through the anterior margin of the pectoral fin base: not necessarily the greatest body depth.
Body length	For larvae: Size of the larva; corresponds to notochord length in preflexion and flexion larvae and to standard length after flexion.
Body width	For larvae: The transverse distance between body margins at the pectoral fin base.
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

C
Canines	conical teeth which are longer than other teeth
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
Cartilage	Cartilaginous. A gristle-like material that supports parts of the body (the tip of your nose is a good example). The skeletons of sharks are composed of cartilage.
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
Choroid fissure	Line of juncture of invaginating borders of the optic cup; apparent in young fish as a trough like area below lens.
Choroid tissue	An undifferentiated mass of (usually) unpigmented tissue adhering to the ventral surface of the eye (see Moser and Ahlstrom 1970)
Chromatophore	A modified dermal cell that contains pigment and gives the fish its colour.
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
Cleithrum	Prominent bone of pectoral girdle, clearly visible in many fish larvae.
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
Continental shelf	the region of the seabed extending from the coast down to a depth of around 200 m
Continental slope	the region of the seabed that slopes down from a depth of around 200 m (the edge of the continental shelf) to around 2000 m
Countershading	body colouration which is dark above and lighter below
Cranium, Cranial	the skull, pertaining to the skull
Crenulate	having the edge slightly scalloped
Cusp	a point or projection on a tooth
Cutaneous	pertaining to the skin
Ctenoid	rough-edged
Cycloid	smooth-edged

D

D
Deciduous	easily removed / rubbed off, temporary, falling off
Demersal	living on or near the sea bed
Demersal egg	An egg which remains on the bottom either free or attached to the substratum.
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

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
Etymology	The study of word origins and derivation.
Eye diameter (ED)	The horizontal distance across the midline of the pigmented region of the eye.

F

E
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
Fin elements	Fin supports; spines and soft rays.
Finfold	Medial fold of integument that extends along body of developing fishes and from which medial fins arise.
Fin length	Length of the longest soft ray of designated fin.
Finlet	a small fin, positioned behind the dorsal or anal fins, that is supported by a ray or rays
Flexion	Bending upward of the notochord tip as part of the process of caudal-fin formation.
Flexion larva	Development stage beginning with flexion of the notochord and ending with the hypural bones assuming a vertical position.
Fluviatile	living in rivers
Fork length	The length of a fish as measured from the tip of the snout to the fork of the caudal fin. Often used for angling species.
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

G
Gas bladder	Membranous, gas filled organ located between the kidneys and alimentary canal in teleost fishes; air bladder or swim bladder.
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
Gonads	the sexual organs which produce eggs or sperm
Gonopodium	a modification of the anal fin of some male fishes, that is used to transfer reproductive products to the female
Gravid	sexually ripe
Gular region	pertaining to the region behind the chin and between the sides of the lower jaw

H

H
Heart	the large muscle which pumps blood around the circulatory system
Head length (HL)	- Adults: The distance from the tip of the snout (or upper lip) to the most posterior point of the opercular margin. - Larvae: The horizontal distance from the tip of snout to posterior most part of opercular membrane; prior to development of operculum, measured to the posterior margin of cleithrum.
Head width	The transverse distance between margins at the widest area of the head. Not applicable to larvae with flared opercles.
Herbivore	an animal that eats plants
Heterocercal	pertaining to the shape of a tail with a long upper lobe and a shorter lower lobe
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.	the flattened bony plate at the posterior end of the vertebral column, formed from parts of the posterior vertebrae.

I

I
Ichthyocide	a substance used to kill (and usually collect) fishes
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
Incipient fin ray	Early stage in fin-ray development; an unossified thickening in finfold articulating with the fin base.
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

J
Jugular	pertaining to the throat
Junior synonym	where more than one scientific name has been used to describe a species, all but the oldest name (the senior synonym) are junior synonyms.
Juvenile	Developmental stage from attainment of full external meristic complements and loss of temporary specializations for pelagic life to sexual maturity.
Juxtaposed	placed near together

K

K
Kidneys	organs involved in excretion and regulation of water balance

L

L
Labial	pertaining to the lips
Labial furrows	shallow grooves around the lips
Labial papillae	small fleshy projections around the lips
Lacrymal, lachrymal	The anterior bone of the infraorbital series. Frequently overlaps the maxilla when the mouth is closed.
Lanceolate	spear-shaped, gradually tapering toward the extremity
Larva	Developmental stage between hatching (or birth) and attainment of full external meristic complements (fins and scales) and loss of temporary specializations for pelagic life; yolk sac through postflexion stage inclusive.
Lateral	at or toward the side
Lateral line	a series of muciferous tubes forming a raised line along the side of the body
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
Lyosphaera stage	A specialized pelagic juvenile stage in the genus Chilomycterus, where elongate papillae develop, but these fail to form spines. Spines do not form until after the pelagic juvenile settles to demersal habitats.

M

M
Mandible	the lower jaw
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
Melanin	A black pigment.
Melanophores	Melanin bearing cells (brown to black); frequently capable of expansions and contractions which change their size and shape.
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
Mouthwidth	The gape; transverse distance between corners of the mouth.
Muciferous	producing or containing mucous or slime
Myosepta	Connective tissue partitions separating adjacent myomeres.
Myotomes	Serial muscle bundles of the body.

N

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	Longitudinal supporting axis of body which is eventually replaced as a support by the vertebral column in teleostean fishes.
Notochord length	Straight line distance from tip of snout to posterior tip of notochord; used prior to and during flexion.
Nuchal	pertaining to the nape

O

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
Oesophagus	the gullet
Olfactory organs	the organs used for smelling, commonly beneath the nostrils
Olfactory pit	A shallow depression on the snout from which olfactory organ develops.
Omnivore	an animal with a diet that consists of both plant and animal material
Opercule, operculum	the bony flap that covers the gills
Opercular	pertaining to the operculum
Opercular spine	spine projecting from the operculum
Orbit	the eye socket
Origin	the most anterior point of a fin base
Osseus	bony
Ossicle	A bony plate.
Ossification	Hardening of bony parts through deposition of calcium salts; usually detected by staining with alizarin.
Osteological	pertaining to bones
Osteology	the study of bones
Otic capsule	Sensory anlage from which the ear develops; clearly visible during early development.
Otolith	Calcareous structures in the ear capsules of bony fishes. Also known as ear bones.
Ovate	egg-shaped
Oviparous	a species that produces eggs that are hatched outside of the body of the female.

P

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 bud	Swelling at site of future pectoral fin; anlage of pectoral fin.
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	usualy 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. In the water column as distinct from substrate associated; neither necessarily planktonic nor oceanic.
Pelagic egg	Egg which floats freely in the water column, often slightly positively buoyant.
Pelagic juvenile	Pre settlement juvenile of a species that is benthic or reef associated as an adult.
Pelvic bud	Swelling at site of future pelvic (ventral) fin; anlage of pelvic fin
Pelvic girdle	the bones to which the ventral fins are attached
Pelvic fins	paired fins behind or below the pectoral fins
Peritoneum	the membrane lining the abdominal cavity
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
physostomus swim bladder	swim bladder connected to the gut
physoclistous swim bladder	swim bladder not connected to the gut
Piscivorous	an organism that feeds upon fishes
Planktivore	an animal with a diet that consists mainly of plankton
Postanal myomeres	Myomeres posterior to the posterior margin of the anus; includes terminal myomere from which urostyle forms.
Posterior	towards the hind end of the fish
Postflexion larva	Developmental stage from formation of the caudal fin (hypural elements vertical) to attainment of full external meristic complements (fin rays and scales) and loss of temporary specializations for pelagic life.
Postorbital	behind the eye
Preanal length (PAL)	Distance from the tip of the snout along the midline to a vertical line through the posterior edge of the anus.
Precaudal	anterior to the tail portion
Pre dorsal fin length	Distance from the tip of the snout along the midline to a vertical line through the origin of the dorsal fin or dorsal fin anlage.
Preflexion larva	Developmental stage beginning at hatching and ending at the start of upward flexion of the notochord.
Pre gas bladder length	Distance from the tip of the snout along the midline to a vertical line through the anterior edge of the gas bladder.
Prehensile	adapted for holding, such as the tail of a seahorse
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)
Preorbital	the area under and in front of the eyes
Pre pelvic fin length	Distance from the tip of the snout along the midline to a vertical line through the origin of the pelvic fin.
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

R
Ramus	one branch or one half of the jaw
Ray	a jointed rod which supports a fin. Many fish have two dorsal fins, the first is usually supported by spines and the second is usually supported by rays. (see also Spine)
Retrose	turned backward
Rostrum	a projecting snout or beak
Rugose	rough

S

S
Scalation	pertains to the pattern/arrangement/presence of scales
Scute	any external horny or bony plate
Senior synonym	the oldest name used to describe a species
Serrate	notched like a saw
Setae	bristles or hairs
Settlement	Process by which a larva or juvenile leaves the pelagic environment and adopts a substrate associated lifestyle; not applicable to species pelagic as adults.
Settlement stage	Developmental stage where the pelagic larva or juvenile is morphologically and physiologically ready (competent) to adopt a substrate associated life style. Often, but not always, associated with larva to juvenile transition. Applicable only to species that are not pelagic as adults.
Sexual dimorphism	differences in physical appearance between the sexes
Snout length (SnL)	Horizontal distance from the tip of the snout to the anterior margin of the pigmented region of the eye.
Soft dorsal	the posterior part of the dorsal fin which is composed of jointed rays
Soft rays	Bilaterally paired, usually segmented fin supports; often referred to as 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 (see also Ray)
Spine length	Straight line distance of a fin or body spine from base to tip.
Spines	Unpaired, unsegmented, unbranched fin supports, usually (but not always) stiff and pungent; may initially form as bilaterally paired structures prior to ossification. - Bony, pointed, elongate projections on the body, usually the head, that are often temporary specializations for pelagic life.
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 hypural plate, the expanded bones at the end of the backbone that support the caudal fin.
Sub- (a prefix)	less than, somewhat, not quite, under
Submarginal	almost at the edge
Suborbital	below the eye
Suborbital stay	a bony, often spine-bearing, ridge 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	Symmetrical: similarly arranged on both sides
Synonym	a different word having the same or a similar meaning
Swimbladder	a sac filled with gas, lying beneath the backbone
Symbiosis	used to describe any association between two organisms. From a Greek word meaning 'living together'.
Symphysis	the junction of two bones of body elements, often used to describe the middle point at the front of the jaws
Synonym	one of two or more names that have been used to describe the same species
Systematics	The study of the evolutionary and genetic relationships between organisms.

T

T
Tail	In larvae - the portion of body posterior to the anus.
Taxonomy	the science of classifying organisms
Teeth	Larvae of some species develop 'larval teeth' prior to the appearance of definitive teeth. Larval teeth are little exserted spines on the premaxilla or dentary, and they are lost during the larval phase (Baldwin 1990).
Teleost	a large group containing most of the bony fishes
Temporary specializations for pelagic life	Morphological (not pigment) characters such as trailing guts, preopercular spines, or elongate fin spines that are not retained in adults but are present during the pelagic phase. Often these are lost after settlement, but if present in settled individuals, they are clearly reduced and are disappearing.
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 (TL)	The length from the tip of the snout to the tip of the tail. - For larvae: Distance from the tip of the snout along the midline to the posterior edge of the caudal finfold; body length is traditionally expressed as total length in the Japanese literature.
Transition	Change from the larval to the juvenile stage. May take place over an extended period of time. Especially used for pelagic taxa where there is not a change in habitat at or near the end of the larval phase. Individuals in transition are considered larval.
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 anus, 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 eg Sydney Harbour

U

U
Undulated	waved
Uniform (as applied to colouration)	of one colour
Unspecified length	Undefined measurement of body length derived from the literature.
Urogenital papilla	a papilla through which the urinary waste and gametes leave the body

V

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
Vent to anal fin length	Straight line distance from posterior edge of the vent (anus) to the anterior origin of the anal fin or anal fin anlage.
Vertebrae	the bones of the spinal column
Vertebrate	an animal with a backbone
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
Viviparous	a species that gives birth to live young. The developing embryo is nourished within the body of the female.
	a bone forming the front part of the roof of the mouth
Vomerine teeth	teeth on the vomer (see above)

X

X
Xanthism (xanthic, xanthochroism)	An unusual colour variety in which the normal colouration of a fish is largely replaced by yellow pigments.
Yolk sac	A bag like, ventral extension of the primitive gut containing the yolk.
Yolk sac larva	Developmental stage beginning with hatching and ending with exhaustion of yolk reserves and characterized by presence of a yolk sac.