Glossary of fish terms

This page lists many of the terms used throughout the site.

Parts of a fish - skeleton

Mark McGrouther © Australian Museum

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  
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  
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  
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  
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  
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  
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  
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.
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  
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  
Kidneys organs involved in excretion and regulation of water balance
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  
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  
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  
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.  As seen on the clavus of Sunfishes.
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  
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
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  
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  
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
  1. Unpaired, unsegmented, unbranched fin supports, usually (but not always) stiff and pungent; may initially form as bilaterally paired structures prior to ossification.
  2. 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
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  
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)
  1. The length from the tip of the snout to the tip of the tail.
  2. 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  
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  
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.
Vomer a bone forming the front part of the roof of the mouth
Vomerine teeth teeth on the vomer (see above)
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.

 

Further reading:

  1. Gomon, M.F., Glover, C.J.M. & R.H. Kuiter (Eds). 1994. The Fishes of Australia's South Coast. State Print, Adelaide. Pp. 992.
  2. Helfman, G.S., Collette, B.B. & D.E. Facey. 1997. The Diversity of Fishes. Blackwell Science. Pp. 528.
  3. McCulloch, A.R., 1934. The Fishes and Fish-Like Animals of New South Wales. Ed 3. With Supplement by G. P. Whitley. Royal Zoological Society of NSW. pp i-XXvi, 1-104, Pl i-xliii.

 


Mark McGrouther , Collection Manager, Ichthyology
Last Updated:

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