Abdomen – the lower surface of the body, especially the part between the pectoral fins and the anus

Abdominal pelvic fins – said of pelvic fins when located on abdomen, far removed from head

Accessory caudal rays – short rays on the upper and lower anterior portions of the caudal fin

Accessory pectoral (or pelvic) scale – see axillary

Adhesive – sticking; clinging. An adhesive egg adheres to substrate or other eggs

Adipose eyelid – transparent tissue around margin of eye

Adipose fin – a fleshy fin on the back behind the dorsal fin as in salmons, smelts, and lanternfishes

Air bladder – see swim bladder

Alevins – newly hatched, incompletely developed fishes (usually salmonids) still in nest or inactive on bottom, living off stored yolk

Ammocoete – a name applied to the larval form of lampreys

Amphicoelous – concave both before and behind, the usual condition of fish vertebrae

Anadromous – ascending rivers from the sea to spawn, as do shad and some salmonid fishes

Anal – referring to the anus or vent

Anal fin – the fin on the median ventral line behind the anus

Anal papilla – an appendage or protuberance in front of the gential pore and behind the vent in sculpins

Annulus – mark or marks formed on fish scale or otolith each year

Anterior – the front portion; in front

Antrorse – turned forward (of maxillary)

Anus – the posterior external opening of the alimentary canal; the vent

Articulated – attached by means of a movable joint; jointed

Axillary – with reference to inner base of pectoral or pelvic fin; site of scale-like process called pectoral or pelvic axillary process

Axillary process – see axillary

Barbel – an elongated, hair-like projection, usually about the mouth, chin, or nose, as in the cods and sturgeons

Basibranchials (or hydroids) – the three median bones on the floor of the gill chamber, joined by the ventral ends of the five gill arches

Basihyal – the median bone which joins the basibranchials posteriorly and which forms the tongue anteriorly, in the floor of the mouth

Black eels – freshwater stage of eels caught in the fall; a Canadian fishermen’s term

Branchial – of the gills

Branchiostegals (or branchiostegal rays) – bony rays supporting the membranes which close the branchial or gill cavity

Breast – see pectoral

Bronze eels – adult eels, fat and nearly mature, ready to migrate to sea for spawning; corresponds to “black eels”

Buccal – of the mouth

Caecum – a blind sac connected with the alimentary canal

Canines – conical teeth which are larger than the rest

Cardiform – brush-like, said of fine teeth of uniform length in brush-like bands or patches

Carinate – keeled; having a sharp median ridge as on the belly of certain herring-like fishes

Caruncles – naked fleshy outgrowths

Catadromous – going down rivers to the sea to spawn as does the American eel

Catadromous migration – refers to run made by a freshwater fish into the sea to spawn

Caudal – pertaining to the tail or caudal fin

Caudal peduncle – the fleshy end of the body behind the anal fin and before the caudal or tail fin; the tail minus the tail fin

Centrum – the body of the vertebrae

Ceratohyal – the anterior bone to which the bases of the branchiostegal rays are attached

Chin – anterior ventral portion of the lower jaw

Chondrocranium – the cartilaginous brain case in bony fishes around which covering bones are laid down

Chorion – outer membrane of an egg; shell

Cirrus – fine or compound and thin flexible appendage or fringe

Civelles – French slang for elvers

Claspers – modified inner portions of the pelvic fins in sharks, rays, and chimaeras; used for sperm transfer to female

Cleithrum – vertical bone in pectoral girdle which supports posterior edge of the gill opening; considered the posterior edge of the gill opening; considered the posterior limit of head length in early larvae

Cloaca – a chamber in the lower part of the gut into which the ducts from the kidney and reproductive organs empty and having one external opening, the cloacal aperture, instead of separate anal (vent) and urinogenital openings

Compressed laterally – flattened from side to side, as of a fish’s body

Confluent – flowing or running together, as where, in certain fishes, dorsal and anal fins are continuous with caudal fin

Ctenoid – said of scales of most spiny-rayed fishes having posterior margins with needle-like projections (rough to the touch)

Cusp – a point or projection on a tooth

Cycloid – said of the scales of typical soft-rayed fishes having smooth posterior margins (smooth to the touch)

Deciduous – said of scales that are easily rubbed off and thus firmly attached

Demersal – living on or near bottom of lake or sea, as said of fishes and of fish eggs

Dentary – a bony element of the lower jaw usually bearing teeth

Dentate – with tooth-like notches

Denticulated – having fine tooth-like projections

Dentition – said of teeth; their arrangement and structure

Diadromous – pertaining to fishes that migrate between fresh and salt water

Dimorphism – existence in two forms

Distal – farthest from the base or point of attachment

Dorsal – pertaining to the back

Dorsal fin – the fin on the back, usually central in position

Elver – small cylindrical young eel (64-76 mm) after acquisition of pigment

Emarginate – said of caudal fin having a slight, shallow notch at the tip

Epihyal – posterior bone to which the bases of the branchiostegal rays are attached

Epipelagic – said of organisms inhabiting aquatic environment between surface and a depth of 200

Falcate – scythe-shaped

Falciform – see falcate

Filament – slender or tread-like structure, said of certain elongated fin rays in some fishes

Filamentous – see filament

Fimbriate – having a frilled edge

Finfold – median fold of integument extending along body of larva and from which the dorsal, caudal, and anal fins are developed

Fingerling – young fish, usually late in the first year

Finlet – a small detached fin or fins following the dorsal and anal fins

Flexion – flexing of urostyle dorsally concurrent with development of hypural bones and other caudal-supporting structures

Fork length – distance from the most anterior part of the head to fork of tail or caudal fin

Fry – young fish, newly hatched, after yolk has been used up and active feeding commenced

Fulcrum – spine-like structure (or structures) bordering the anterior rays of the fins in some fishes

Fusiform – spindle-shaped; referring to the form of fishes that have the body tapering both anteriorly and posteriorly, and slightly or not at allcompressed

Gape (of the mouth) – the distance from the front to the angle of the mouth, crude index of size of the mouth, crude index of size of mouth; habit of spawning fishes of opening mouth very widely

Gas bladder – see swim bladder

Genital papilla – a projection near the anus that carries the external opening to the reproductive system

Gill arches – the bony supports of the gills

Gill cover – see operculum

Gill membrane – the thin wall of skin supported by the branchiostegals, and closing the gill cavity below

Gill rakers – a series of tooth-like bony structures placed along the anterior edge of the gill arches

Glass eels – first oceanic stage of eels after metamorphosis from leptocephalus; they resemble adults but lack pigment

Graduated – regular or steady increase in length, as of the spines in the fins of some fishes

Gular plate – bony plate (or plates) located behind the chin and between the sides of the  lower jaw

Haemal spine – the lower or ventral spine of a caudal vertebrae

Head length – distance from the most anterior point of the head to the posterior edge of the opercle

Heterocercal – unequally lobed; said of the tail or caudal fin of a fish where the upper lobe is larger than the lower, and in which the last few vertebrae or the vertebral column are bent upward

Homocercal – equally lobed; said of the tail or caudal fin when upper and lower lobes are more or less equal, and the backbone or vertebral column ends at the middle of the base of the fin

Humeral – in reference to humerus, used to designate spine at base of pectoral fin of Lophius

Hyoid – see basibranchial

Hypurals – the expanded haemal spines of the posterior vertebrae

Illicium – modified fin ray located on head of anglerfishes and relatives; the fishing rod of angler fishes

Imbricated – overlapping, like shingles on a roof

Inferior – used in reference to mouth when snout projects beyond lower jaw

Infraoral – below the mouth; used in reference to the teeth of the mouth immediately below the oesophageal opening in lampreys

Interneurals – the bones to which the dorsal fin rays are attached

Interopercle – a bone of the lower part of side of the head; a part of the operculum

Interorbital space – narrowest distance across the head, between the bony edges of the orbits or eye sockets

Isocercal – with the vertebrate becoming progressively smaller backward, as in the codfishes

Isopondylous – with the anterior vertebrae simple; said of the herring-like fishes which lack the Weberian apparatus

Isthmus – the fleshy structure beneath the head and between the gill-openings

Jugular – pertaining to the throat; said of the pelvic fins when located in advance of the point of attachment of the pectorals

Juvenile – young fish, fundamentally like the adult in meristic characters (excluding scalation) but smaller and reproductively inactive

Keel – a sharp compressed edge on the ventral surface of the body between the paired fins; or on the lateral surface of the caudal peduncle

Keeled – see carinate

Kelt – a dark, thin, recently spawned-out Atlantic salmon

Kype – the hooked end of the lower jaw of male salmons and trouts; develops at spawning time

Lateral line – series of pore-like openings (to sensory canal) along the sides of a fish

Laterally compressed – flattened from side to side

Leptocephalus – a name applied to the larval form of the eels

Lingual – pertaining to the tongue

Lingual teeth – teeth on tongue; the serrated teeth on the tongue of lampreys

Luminous organ – an organ that produces light; usually on abdomen or head, as in lanternfishes

Lunate – crescent-like, in reference to shape of caudal or tail fin

Major rays (or principal rays) – longer (at least ¾ height of fin) obvious fin rays as opposed to anterior rudiments which are often not visible; often comprise all branched rays plus one anterior unbranched ray

Mandible – the lower jaw

Maxillary – the posterior element of the upper jaw

Melanophore – black pigment cell

Meristic characters – countable structures occurring in series

Myomere – body segment; vertebrae

Myotome – a muscle plate; a section of the repeated muscle units corresponding to the flakes of a cooked fish

Nape – part of body immediately behind head on dorsal surface

Nasal – one of the paired bones on front of a fish’s head, usually beside the nostril

Neural spine – the upper or dorsal spine of a vertebra

Notochord – the embryonic cartilaginous vertebral column persistent in lampreys, sharks, and rays

Notochord length – a straight line measurement from tip of snout to posterior tip of notochord

Nuptial tubercles – small often pimple-like projections that occur on head or body or lower fins of males of some species during breeding period

Occipital crest – bony ridge, usually serrated, on top of head

Occiput – the extreme back of the head on dorsal surface

Ocellus – an eye-like spot

Oesophagus – the beginning of the digestive tract immediately after the mouth

Oil globules – discrete spheres of fatty materials with buoyant properties within the yolk of eggs of some fishes

Opercle – the large rectangular bone on the gill cover

Opercular flap – a backward prolongation of the posterior or angle of the opercle

Opercular gill – a rudimentary gill on the inner face of the operculum as in gars and sturgeons

Operculum – the bony covering of the gill cavity composed of opercular bones

Opisthocoelous – convex in front, concave behind, the condition in the vertebrae of gars

Orbit – the bony eye socket

Origin – of a fin – the anterior end of the base; the end of the base nearest the head

Otic – pertaining to the ear

Otoliths – calcareous concretions in the internal ear, especially of teleost fishes (often called ear-stones); frequently used in aging studies

Oviparous – said of fishes that deposit eggs which develop usually in the external environment

Ovoviviparous – said of those fishes that retain the eggs within the body of the female in a brood chamber in which the development of the embryo takes place, perhaps deriving some nourishment from the female, but without the strong umbilical attachment to a placenta as in mammals; the true condition of ‘live-bearing’ fishes

Paired fins – pectoral and pelvic fins, in contrast to vertical fins

Palatine – a paired bone of the roof of the mouth

Papilla – a small fleshy projection

Papillose – covered with papillae

Parietal – one of the roofing bones of the skull

Parr – life stage of salmonid fishes, usually in first or second year, when body is marked with parr marks

Parr marks – dark ventral marks on the sides of young salmonid fishes

Pectinate – having teeth like a comb

Pectoral – the anterior ventral portion of a fish

Pectoral arch – shoulder girdle; the complex of bones, usually connected with the skull, to which the pectoral fins are attached

Pectoral fins – the most anterior or uppermost of the paired fins, usually dorsal to pelvic fins

Pectoral girdle – see pectoral arch

Peduncle – the fleshy end of the body behind the anal fin

Pelvic arch or girdle – the bones to which the pelvic fins are attached; public bones

Pelvic axillary process – a slender scale-like process or tab of tissue that develops at the base of the pelvic fins of many salmonid and other bony fishes

Pelvic fins – the most ventral of the paired fins; positioned on ventral surface, usually articulated with pelvic girdle

Percomorph – used in reference to those fishes in the order Perciformes and their highly specialized relatives

Peritoneum – the membranous inner lining of the abdominal cavity

Perivitelline space – fluid-filled space between the fertilization membrane and chorion of a fish egg

Pharyngeal bones – bones behind the gills opposed to each other and usually armed with teeth, immediately before the oesophagus

Photophore – an organ that produces light, usually on belly or head, as in lanternfishes

Physoclistous - having the swim bladder isolated from the oesophagus

Physostomous – having the swim bladder connected to the oesphagus by an open duct

Piscivorous – fish-eating

Posterior – behind

Postorbital – situated behind the orbit

Prefrontal – a roofing bone of the skull, located anteriorly

Premaxillary – the paired bones usually bearing teeth that form the front of the upper jaw  in trout-like fishes, and the entire border of the upper jaw in higher percomorph fishes

Preopercle – the most anterior of the opercular series of bones; the bone of the cheek

Preorbital – a large bone lying in front of the eye

Prickles – small, fine, sometimes curved spines, on, or in place of, scales

Principal rays – see major rays

Procurrent – adjective applied to the stiff rays at base of caudal fin

Proximal – nearest the point of attachment

Pseudobranch – a rudimentary gill on the inner face of the operculum

Pterotic – bone in the outer dorsal portion of the optic capsule in many fishes

Pterygiophores – cartilaginous or bony elements by which fin rays of a fish are supported

Pyloric – used in reference to the pylorus, that section of the intestinal tract immediately following the stomach

Pyloric caeca – blind sacs attached to the pyloric section of the digestive tract

Ray – an articulated and segmented rod that supports the membrane of a fin

Redd – the gravel nest of salmonid fishes

Rostral cartilage – cartilaginous rod extending from the chondrocranium or skull to the snout in skates; usually visible with transmitted light

Rostrum – a bony extension of the snout as in a swordfish

Redimentary – undeveloped

Scale radii – lines or grooves on a scale radiating from the focus (center of scale) to the margin; often obvious on ctenoid scales

Sculptured – property or eggshell (chorion) bearing distinctive marks, convolutions, or other ornamentation

Scute – a bony or horny plate

Serrate – saw-toothed; like a saw

Shoulder girdle – the complex of bones usually connected with the skull, to which the pectoral fins are attached

Smolt – life stage in salmonid fishes; individual usually 1-3 years of age, turning silvery, preparing to migrate out of stream or lake or sea, or out of stream to large lake

Snout – technically that part of the head of a fish in front of the eyes

Soft dorsal – the dorsal fin or portion of it which consists of soft rays only

Spine – a fin ray which is not branched, is without obvious segments, and is more or less stiffened and sharpened at the apex; used also in reference to skin spines on skates

Spinous dorsal – the dorsal fin or portion of it which consists of spines only

Spiracle – an opening in the head anterior to and above the opercular opening representing a primitive gill-cleft, in lampreys, hagfishes, sharks, and rays

Spiral valve – a spiral infolding (ridge) of the wall of the intestine

Standard length – distance form the most anterior part of the head to the posterior margin of the last whole vertebral centrum

Stay (or membranous connection) – a fleshy bridge from side of body to upper base of pelvic fin

Subopercle – the bone below the opercle (see operculum)

Suborbitals – a series of small bones below the eye

Subterminal mouth – set back from anteriormost point of snout

Supplemental maxillary – a small bone lying on the upper posterior edge of the maxillary

Supraoccipital – the unpaired bone at the back of the skull usually with a crest above

Supraoccipital crest – the posterior median ridge on the back of the skull

Supraoccipital spine – spine or crest on midline of the occiput

Supraoral – above the mouth

Swim bladder – a sac filled with air or other gases lying beneath the backbone and either attached or not to the walls of the body cavity

Symphysis – the point of junction of two bones as in the two parts of the lower jaw in front: the tip of the chin

Tail – the portion of the body of a fish posterior to the anus

Teleost – a name applied to fishes having the skeleton fully ossified; in other words a “bony fish” in contrast to a shark, which is a cartilaginous fish

Telescopic eye – an eye (not on a stalk) protruding within an envelope of skin

Terminal mouth – located at termination of the head

Thoracic – pertaining to the chest or thorax; anterior to the abdomen

Thoracic pelvic fins – pelvic fins which are attached far forward below the pectorals, the pelvic bones usually connected with the shoulder girdle

Tooth formula – numerical expression of the number of teeth in each of one or more rows

Total length – straight-line measurement from most anterior point to most posterior point of a fish

Tubercle – a soft hardened lump or projection on the surface; usually a modified scale

Urostyle – the last vertebral segment, usually modified (pointed) and reduced

Velar tentacle – a membranous finger-like projection that, in lampreys, lies at the junction of the respiratory tube and oesophagus

Vent – the external opening of the alimentary canal; the anus

Ventral – on the lower surface; pertaining to the abdomen or belly

Ventral fins – see pelvic fins

Vertical fins – the fins (dorsal, anal, and caudal) on the median (center) line of the body, in contrast to the paired fins (pectorals and pelvics)

Vexillifer larva – larva with a vexillum, which is a long thread-like process anterior to the dorsal fin

Villiform – of the form of villi (finger-like projections); said of teeth which are slender and crowded closely together in bands

Viviparous – giving birth to live young; said of some species of sharks in which the embryo becomes attached to the uterine wall by a yolk-sac placenta and is nourished by the female until gestation is completed

Vomer – the anterior bone on the roof of the mouth

Yolk-sac larva – early larva containing yolk in a sac in the gut region