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A

abbreviation for anal fin

Abdominal

gut region

Abbreviate heterocercal

tail in which the vertebral axis is prominently flexed upward, only partly invading upper lobe of caudal fin; fin fairly symmetrical externally

Actinotrichia

horny fin supports (threadlike fibers) which are the precursors of fin rays or spines (lepidotrichia)

Adherent

attached or joined together, at least at one point

Adhesive (egg)

referring to eggs, those which stick to each other or to a substrate after water hardening, unless otherwise noted; adhesiveness of entire egg capsule may or may not persist after attachment

Adhesive organ

a suctorial organ, located anteriorly on snout, which produces a viscid secretion allowing larva to attach to objects

Adipose fin

fleshy, rayless fin posterior to (behind) the dorsal fin (between dorsal and caudal fins)

Adnasal pore

pore at the end of the short, ascending branch of the infraorbital canal, which lies just behind the anterior nostril; not always present (eels)

Adnate

joined to; grown together

Adnexed

flaglike

Adult

sexually mature as indicated by production of gametes

Air bladder

see: swim bladder

Alevin

a term applied to juvenile catfish, trout, and salmon after yolk absorption; exhibiting no post yolk-sac larval phase

Aliform

wing-like; usually referring to the shape of the pectoral fin

Allopatric

having separate and mutually exclusive areas of geographic distribution

Anadromous

referring to fishes that ascend rivers to spawn

Anal

pertaining to the anus or vent

Anal fin

fin (usually single but double in some gadiforms) on the ventral margin of the tail; unpaired median fin immediately behind anus or vent

Anal fin origin

anterior-most point at which the anal fin attaches to the body

Angle of jaw

bony prominence posterior to gape of jaw; region of the junction of the angular, articular, and quadrate bones

Angular

the bone at the angle of the jaw or that region; used in reference to pigmentation at, or near, the angular bone

Anlage(n)

rudimentary form of an anatomical structure or organ; primordium

Anterior

towards the front; cephalad

Antero-hyal

anterior bone to which branchiostegal rays attach: formerly ceratohyal

Antrorse

angled forward; usually referring to direction of a spine

Anus

orifice and surrounding tissue at the terminus of gut; external orifice of the intestine; vent

Aorta

main blood vessel lying below the spinal chord that supplies blood from the heart

Articular

a bone of the lower jaw between the dentary and angular bones (some consider it part of the angular); used in reference to pigment anterior to the angle of the upper jaw

Auditory vesicle

sensory anlage from which the ear develops; clearly visible during early development

Axillary process

enlarged accessory scale attached to the upper or anterior base of pectoral or pelvic fins

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B

BDA

body depth at anus

BL

body length

Band

a strip of pigment that contrasts with the adjacent background pigment or unpigmented area; it may be on any part of the head, body, or fins and may be oriented in any position; a vertical band occurring laterally on the head or body is referred to as a bar and a horizontal band is referred to as a stripe

Bar

a vertical band of pigment on the lateral surface of the head or body; often occurring in a series

Barbel

slender sensory projection on the lips or chin; barbel length measured from the point of attachment on the head to the tip of the barbel

Basibranchials

three median bones on the floor of the gill chamber, joined to the ventral ends of the five gill arches

Basin

a large complex of rivers or lakes with a single outlet to the ocean (e.g., Great Lakes)

Basipterygium

bone or process that supports the pelvic fin

Bathypelagic

zone below 1,000m depth in the open ocean

Benthic

living on or in the bottom (substrate)

Bicuspid

having or ending in two points; a tooth with two points

Blastocoel

cavity of the blastula; segmentation cavity

Blastoderm

specifically, early embryonic tissue composed of blastomeres; more generally, embryonic tissue prior to formation of embryonic axis

Blastodisc

early embryo of teleosts consisting of a disc-or cap-like mass of cells on the yolk; embryo-forming area of egg prior to cleavage

Blastomere

individual cells forming the early embryo of teleosts (during cleavage)

Blastopore

opening formed by and bordered by the germ ring as it extends over the yolk

Blastula

stage in embryonic development which represents the final product of cleavage stages, characterized by formation of the blastocoel

Body depth

the vertical distance from the dorsal margin of the body to the ventral margin of the body measured at the base of the pectoral fin where it attaches to the body; fins or fin bases are not included in the measurement

Body depth at anus

vertical distance of body at anus

Body length

general term used to indicate the size of a larva; equivalent to notochord length (distance from the tip of the snout to the tip of the notochord) in preflexion and flexion stage larvae and equivalent to standard length (distance from the tip of the snout to the posterior margin of the hypural plate) in postflexion larvae. In beloniform fishes, body length measured from the end of the opercle to the caudal base because of allometry and because the beak is often broken

Branched ray

soft ray with two or more branches distally

Branchial arches

bony or cartilaginous structures, supporting the gills, filaments and rakers

Branchial pores

pores in branchial region of lateral-line canal (eels)

Branchial region

in petromyzontids, area between the anterior margin of the first gill opening and the posterior margin of the last

Branchiostegal membrane

membrane connecting the elongated bones which ventrally support the gill membranes

Branchiostegal rays (branchiostegals)

bony rays supporting the membranes which close the gill (branchial) cavity under the head; ray-like bony elements attached to the hyoid arch, extending under the gill openings and connected by a membrane

Bud

the undifferentiated bump or protuberance that appears at the initial formation of the paired fins

Buoyant egg

an egg which floats free within the water column; pelagic

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C

abbreviation for caudal fin

CPD

caudal peduncle depth

Caeca

finger-like outpouchings at boundary of stomach and intestine

Calcareous

composed of, containing, or characteristic of calcium carbonate

Cardiform

brush-like; referring to teeth of uniform length in patches or bands

Caruncles

fleshy outgrowths; modified dorsal fin rays in ceratiids

Catadromous

fishes which go to sea from rivers to spawn

Caudal fin

median fin at the posterior end of the fish; tail fin

Caudal peduncle

narrow part of the tail between the posterior end of the anal or dorsal fin and the base of the caudal fin; caudal peduncle length measured from the insertion of the posterior-most ray of the anal or dorsal fin (whichever is most posteriad) to the insertion of the anterior-most caudal fin-ray

Caudal vertebrae

the posterior group of vertebrae extending from the centrum bearing the first haemal spine to the urostyle

Cement glands

discrete or diffuse structures which permit a larva to adhere to a substrate

Centrum

the body of a vertebra

Cephalic

belonging to the head

Cerotohyal

see: antero-hyal

Cheek

lateral surface of head between eye and opercle, usually excluding preopercle

Chevron-shaped

the earliest developmental form of myomeres in larvae; describing the angle formed by the epaxial and hypaxial portions of the myosepta

Chorion

after water hardening, the outermost membrane of a fish egg

Choroid fissure

a cleft in outer layers of the eye visible in early larvae; indentation at the ventral margin of the eye marking the invaginated borders of the optic cup in larval fish; apparent in young fish as a trough-like area below lens

Choroid tissue

mass of primordial vascular tissue of various shapes lying below the eye; usually associated with narrow eyes; often pigmented; its length measured along its longitudinal axis from the interface with pigmented portion of the eye to the tip of the choroid mass

Chromatophore

pigment-bearing cell; frequently capable of expansions and contractions which change their size, shape, and color

Cirrus

generally small, dermal, flap-like or tentacle-like process on the head or body

Cleavage stages

initial stages in embryonic development where divisions of blastomeres are clearly marked; usually include 1st through 6th cleavages (2-64 cells)

Cleithral symphysis or junction

where the ventral ends of the cleithral bones meet

Cleithrum

large bone of support for the pectoral fins; elongate vertical bone in pectoral girdle at the junction of the head and body of the fish; one of the first bones to form in the body; demarcates the junction of the head and body; clearly visible in many fish larvae

Coelomic

belonging to the body cavity

Coiled

condition of the gut where it is twisted or convoluted

Compressed

laterally flattened

Confluent

coming together to form one

Crown

top of the head

Ctenoid scale

scales having small, needle-like projections on the posterior margin; bearing cteni

Cycloid scale

scales with evenly curved free border, without cteni

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D

D or DF

dorsal fin

DFO

dorsal fin origin

Dash (pigment)

an elongate or streak-like melanophore

Deciduous

referring to scales that are easily rubbed off and thus not firmly attached

Demersal (egg)

referring to an egg which rests upon the substrate as a result of deposition or settling; at the ocean bottom; used in reference to life stages from eggs to adults; may be free or attached

Dendritic

highly branched; usually used in reference to a melanophore

Dentary

major bony element of the lower jaw, usually bearing teeth

Depth

greatest depth of body, excluding median fins (taken just behind gill opening, at or behind anus, or elsewhere at greatest depth)

Disk

flat cup-like structure formed from modified pelvic fin rays (also pectoral fin rays in some fishes) used for holding onto the substrate or structures on the substrate (e.g., gobiesocids, cyclopterids, gobioids); its diameter (P2DL) is measured longitudinally from one margin to the opposite margin; in echeneids, the disk is on the top of the head and formed from modified dorsal fin spines; also refers to the disk-shaped head of ogcocephalids where disk width (DW) is the greatest transverse dimension of the disk

Distal

remote from the point of attachment; opposite to proximal

Distribution

occurrence of species in the region (e.g., Great Lakes region and within the Lake Michigan drainage)

Dorsal

upper part of body; opposite of ventral

Dorsal fin

fin or fins on dorsal margin of the body; median, longitudinal, vertical fins located on the back

Dorsal fin origin

point where first dorsal ray or spine attaches to body

Dorsum

uppermost part of body; dorsal body margin; opposite to ventrum

Drainage

a group of lakes or streams within a basin (e.g., Lake Michigan drainage)

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E

ED

eye diameter

Early embryo

stage in embryonic development characterized by formation of embryonic axis

Early life history

the early phase in life, spanning the developmental stages from egg to juvenile

Egg capsule

outermost encapsulating structure of the egg, consisting of one or more membranes; the protective shell

Egg diameter

in nearly spherical eggs, greatest diameter; in elliptical eggs given as two measurements, the greatest diameter or major axis and the least diameter or minor axis

Egg pit

the pit or pocket in a redd (nest) into which a trout female deposits one batch of eggs

Eggs

description of fertilized, water hardened eggs, unless otherwise noted; diameter, color, adhesive properties, buoyancy, yolk and oil globule characteristics and incubation period

Elver

stage of eels after glass eel stage and prior to adulthood, when they become pigmented

Emarginate

caudal fin possessing a slight notch or indentation, but not definitely forked

Embryo

organism at an early stage of differentiation and growth; refers to the stage of development between fertilization and hatching

Embryonic axis

primitive differentiation of the embryo; an elongate thickening of blastodermal tissue

Embryonic shield

thickened area of the germ ring representing the future longitudinal axis of the embryo

Emergence

the act of leaving the substrate and beginning to swim; swim-up

Engyodontic stage

early stage of anguilliform larvae (preceding euryodontic stage) characterized by few needle-like teeth, the upper and lower jaws equal in length, no nasal capsule, an undifferentiated finfold, no hypurals, the notochord tip straight, and the head and preanal region of the body relatively large

Epaxial

the portion of the body above the horizontal myoseptum; the part of the myomeres above the lateral midline (horizontal septum)

Epibenthic

zone at the interface with the sea bottom; refers to organisms living in contact with the sea bottom

Epiboly

movement of embryonic cell mass over the surface of the yolk; the germ ring marks the boundary of the advancing sheet of cells

Epihyal

see: postero-hyal

Epipelagic

zone from the surface to 200m depth in the open ocean

Epurals

modified vertebral elements which lay above the vertebrae and support part of the caudal fin

Erythrophores

red or orange pigment cells

Esca

the lure at the tip of illicium in most lophiiform fishes; commonly luminous in deepsea species

Esophagus

alimentary tract between pharynx and stomach

Ethmoid pore

pore in the ethmoid canal, included in the count for supraorbital pores (eels)

Euryodontic stage

advanced stage of anguilliform larvae (following engyodontic stage) characterized by a relatively smaller head and preanal region, three series of relatively short, broad teeth, a relatively shortened lower jaw, the formation of nasal capsules, fins, and hypurals, and the flexion of the notochord

Eye diameter

horizontal distance of the iris of the eye; in larvae with round eyes, the diameter of the pigmented part of the eye, usually measured through the horizontal midline; in larvae with oval or elliptical eyes, the horizontal dimension is given first, followed by the vertical dimension

Eye length

the longer axis of an oval or elliptical eye measured through the midline from the pigmented margin of one side of the eye to the other side

Eye stalks

movable peduncles of varying length bearing the eyes; eye stalk length measured from the point where the stalk attaches to the head to the point of attachment at the eye

Eye width

the shorter axis of an oval or elliptical eye measured through the midline from the pigmented margin of one side of the eye to the other side

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F

FL

fork length

Falcate

scythe-shaped; referring to an anal fin; deeply concave as a fin with middle rays much shorter than anterior and posterior rays

Fecundity

average number or range of ovarian eggs per female, unless otherwise noted

Fin elements

fin spines, rays, and supporting bones (pterygiophores)

Fin insertion

posterior-most point at which the fin attaches to the body

Fin origin

anterior-most point at which the fin attaches to the body

Fin rays

segmented cartilage or bony structures which support fin membranes

Finfold

median fold of skin surrounding the body within which the dorsal, anal, and caudal fins develop; the part of the ventral finfold in which the anal fin develops is referred to as the anal finfold

Finlet

small fin-like structures posterior to the dorsal and anal fins

First-feeding larvae

larvae that have used all or most of their yolk and are capable of capturing prey

Flexion

stage (or the process) when the urostyle bends dorsally concurrently with the development of principal rays and hypural bones in the caudal fin; also, the process of notochord flexion; preflexion refers to the stage prior to the initial bending of the notochord tip and postflexion refers to the stage after the completion of the notochord flexion

Focal point

location of a fish maintaining a stationary position on or off the substrate for at least a 10-second period

Fontinelle

a gap or space between bones in the roof of the skull covered only by a membrane

Foramen

an opening through a bone

Forebrain

anterior region of the developing brain that includes the olfactory lobes

Foregut

anterior part of the primitive alimentary canal from which the esophagus and stomach develop

Fork length (FL)

distance from the most anterior point on the snout to the end of the shortest central caudal fin ray

Frenum

a fold of skin that limits movement of the upper jaw

Frontal bones

large paired (fused in some species) bones that form the top of the cranium anteriorly; they often from a ridge over each orbit (supraocular crest) that may bear one or more spines

Frontal pore

a single median pore found in the frontal canal, present in some families (eels)

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G

GB

location of the gall bladder

GD

greatest depth

Ganoid scales

diamond- or rhombic-shaped scales consisting of bone covered with enamel

Gape

the border of the mouth

Gargaropteron stage

pelagic stage of the chiasmodontid genus Kali, characterized by greatly elongate pectoral and pelvic fin rays

Gas bladder

see: swim bladder

Gastrula

stage in embryonic development between blastula and embryonic axis

Germ ring

thickened margin of the blastodisc that advances over the yolk during epiboly

Germinal disc

the blastodisc

Gill arch(es)

see: branchial arches

Gill opening

measure distance between upper and lower ends of gill opening

Gill rakers

variously-shaped bony projections on anterior edge of the gill arches

Glass eel

stage of eel following leptocephali stage when they enter estuaries (after pigmentation they are called elvers)

Glossohyal

a median bone of the tongue

Granular yolk

yolk consisting of discrete units of finely to coarsely granular material

Greatest body depth

greatest vertical distance of body excluding fins and/or finfolds

Guanophores

silvery or white pigment cells containing iridescent crystals of guanine

Gular

ventral region of the head anterior to the isthmus and below the lower jaw

Gular fold

transverse membrane across throat

Gular plate

median ventral bony plate or plates located behind the chin and between the sides of the lower jaw, as in Amia calva; large dermal bone on throat

Gular region

throat

Gut

alimentary tube and associated organs

Gut length

distance from anterior margin of yolk sac to vent or from anterior margin of stomach (when distinguishable) to vent

Gut loop

loop, fold, or curve found along the axis of the gut

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H

HD

head depth

HL

head length

HW

head width

Haemal spine

a median spine on the ventral surface of a vertebral centrum, attached to the centrum by two bones that form an arch (haemal arch)

Head length (HL)

distance from the most anterior point on the snout to the posterior edge of the auditory vesicle, cleithrum or opercle as each develop; horizontal distance from the tip of the snout to the posterior margin of the cleithrum; or to posterodorsal point of gill opening, depending upon family

Head width (HW)

greatest dimension between opercles; transverse distance between the lateral margins of the head measured at the posterior margin of the orbit

Heterocercal

caudal fin upper lobe much larger or longer than lower; tail in which the vertebral axis is flexed upward and extends nearly to tip of upper lobe of caudal fin; fin typically asymmetrical externally,

Hindbrain

posterior region of the developing brain that includes the medulla

Hindgut

posterior part of the alimentary canal that includes the intestine and rectum

Holoblastic

type of cleavage in which the entire egg, including the yolk, undergoes division

Homocercal

type of caudal fin in teleosts where the upper and lower lobes are symmetrical; internally, the major structural elements of the fin are an upturned urostyle (several fused vertebrae) that articulates with flattened bones (hypurals and parhypural) that support the principal fin rays

Homogeneous

uniform in composition; opposite to segmented in referring to egg yolk

Horizontal myoseptum / septum

a sheet of connective tissue (in the horizontal plane) that separates the epaxial and hypaxial muscle masses; the lateral midline area in reference to pigmentation

Hyomandibular

bone or cartilage (usually elongate) in the cheek region that functions in jaw suspension

Hypaxial

the portion of the body below the horizontal myoseptum; the part of the myomeres below the lateral midline (horizontal septum)

Hypochord(al)

below the notochord; referring to the lower lobe of the caudal fin; a transitional rod of cells which develops under the notochord in the trunk region of some embryos

Hypurals

the expanded haemal spines of the posterior vertebrae which support most of the caudal fin

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I

Ichthyoplankton

that part of the zooplankton consisting of the egg and larval stages of fishes

Illicium

tentacle-like spine of the dorsal fin located on the snout of most lophiiform fishes, used as a lure to attract prey; illicium length measured from the point of insertion of the illicium on the head to the tip of the structure

Incipient

becoming apparent

Incubation period

time from fertilization of egg to hatching

Inferior

spatial anatomical term meaning lower in position; opposite to superior

Inferior mouth

snout projecting beyond the lower jaw; also referred to as subterminal mouth

Infraorbital

space between eyes over top of head

Infraorbital pores

pores in infraorbital canal, including pores in lateral canal along upper jaw below eye, and postorbital pores (sometimes listed separately) in ascending canal behind eye (eels)

Insertion (of fin)

posterior (usually) point of attachment of a fin

Integument

an enveloping layer or membrane; coating or external skin

Internarial

area between the nares on one side of the head or the other

Interopercle

lower bone of the gill cover lying below the preopercle

Interorbital

region on top of the head between the orbits of the eyes

Interorbital pores

pores in the supraorbital canal which are located between the eyes (eels)

Interorbital width

least distance between the orbits across dorsum of head

Interradial

area between the fin rays

Interspaces

spaces between parr marks in salmonids

Iridocytes

crystals of guanine having reflective and iridescent qualities

Iridophores

see: guanophores

Isocercal

symmetrical tail fin; vertebral column ending along the median line, caudal fin rays arising symmetrically from it; tail in which vertebral axis terminates in median line of fin, as in Gadiformes

Isthmus

fleshy space beneath the head and between the gill openings; ventral region of the head below the gills, often narrow, connecting the gular and cleithral regions; measure interbranchial distance as ventral distance between lower ends of gill opening

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J

Jugular

referring to the throat region; beneath the head; usually used to indicate the position of the pelvic fin in some fishes

Juvenile

phase of development from complete fin ray development and finfold absorption to sexual maturity; stage after transformation from the larval stage that is like the adult but not yet reproductively active; there is a full complement of fin rays, scales are formed (in species that have them), and the form is fundamentally similar to the adult

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K

Keeled

with a ridge or ridges

Kupffer's vesicle

a small, vesicular, ventro-caudal pocketing which forms as blastopore narrows

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L

LIV

location of the liver

Lachrymal

the anterior-most of the infraorbital (circumorbital) bones; enlarged and with spines in some species

Lanceolate

slightly broad at the base and tapering to a point

Larva / larvae

phase of development from complete absorption of yolk to development of the full complement of adult fin rays and absorption of finfold; stage following hatching that is unlike the juvenile or adult in form and pigmentation, and must transform or metamorphose before assuming juvenile/adult characteristics

Last vertical blood vessel

the posterior-most large blood vessel extending from the dorsal aorta to the kidney (nephros); used as reference point and taxonomic character in eel leptocephali

Late embryo

stage prior to hatching in which the embryo has developed external characteristics of its hatching stage

Lateral line

a line along the lateral surface of the body (backward from head along sides) formed by a series of sensory pores that usually are associated with modified scales

Lateral line pores

pores in lateral-line canal (sometimes counted to anus, sometimes total count given) (eels)

Lateral line scales

pored or notched scales associated with the lateral line

Lateral midline

the region of the body between epaxial and hypaxial myomeres; the region of the horizontal septum

Lateral series scales

number of rows of scales crossing the midlateral surface or lateral line if complete

Lateral teeth

in petromyzontids, teeth of oral disc lateral to esophageal opening

Lepidotrichia

replacements of actinotrichia; soft fin rays or spines; scale-like structures that form the segments of soft rays in bony fishes

Leptocephalus (leptocephali)

transparent, ribbon-like, often large larvae of elopiform fishes with an internal cavity filled with acellular mucinous material; leptocephali usually have a small head and prominent teeth

Lithophils

requiring gravel as a substrate for spawning

Live-bearing

see: viviparous

Longitudinal septum

a sheet of connective tissue that separates the muscle masses on the right and left sides; the dorsal longitudinal septum separates the epaxial muscle masses and the ventral longitudinal septum separates the hypaxial masses

Low terminal mouth

mouth that is slightly oblique to horizontal with anterior end of upper lip at or below bottom-of-eye level and either even with or the most anterior margin of snout

Lower jaw

measure from tip of lower jaw to angle of mouth

Lunate

crescent (moon) shaped

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M

mm

millimeter

Mandible

lower jaw, comprised of three bones: dentary, angular and articular

Mandibular pores

pores along lower jaw, part of preoperculomandibular canal series (eels)

Maxilla / maxillae

the posterior, lateral bones of the upper jaw; the longest paired bones of the upper jaw; located above the premaxillae

Maxillary

the dorsalmost of the two bones in the upper jaw

Meckel's cartilage

embryonic cartilaginous axis of the lower jaw in bony fishes

Median

referring to the midline plane that divides a bilaterally symmetrical animal into right and left halves; usually synonymous with mesial

Melanophore

melanin-bearing pigment cell; ameboid black or brown pigment cells of various shapes and sizes derived from the neural crest region of the embryo; black chromatophores

Mental

pertaining to the chin

Meristic characters / meristics

countable structures occurring in series (e.g., myomeres, vertebrae, fin rays)

Meroblastic

type of cleavage in which only the blastodisc undergoes division

Mesencephalon

midbrain; serves optic functions

Mesolarva

phase of larval development (used by Snyder et. al.) characterized by presence of at least one dorsal, anal, or caudal-fin spine or ray but either lacking the adult complement of principal soft rays in at least one median (dorsal, anal, or caudal) fin or lacking pelvic-fin buds or pelvic fins (if present in adult)

Mesopelagic

zone from 200m to 1000m depth in the open ocean

Mesopterygoid

middle of three dermal bones of the upper jaw

Metalarva

phase of larval development (used by Snyder et. al.) characterized by presence of adult complement of principal soft rays in all median fins and pelvic-fin buds or pelvic fins (if present in adult)

Metamorphosis

a marked change in form or structure at the end of the larval stage involving acquisition of adult characters and loss of larval characters; synonymous with transformation

Metencephalon

portion of the brain immediately behind the mesencephalon

Micropyle

principle path of sperm entry through the chorion (vitelline membrane) of an egg

Midbrain

region of the developing brain that includes the optic and cerebellar lobes

Midline

the median plane or line of the body either on the dorsal or ventral surface; sometimes used as the middle of a body part

Molariform

referring to a tooth with a flat grinding surface

Morula

stage in development of egg in which blastomeres from a mulberry-like cluster

Mucosal folds

folds of tissue lining the cavity of the intestine; pronounced in some fish larvae giving a striated or rugose appearance

Myomere formula

preanal myomeres + postanal myomeres = total myomeres

Myomeres

muscle segments of the body occurring in series; approximately equal to number of vertebrae in adults; the preanal myomeres are defined as all myomeres anterior to a vertical from the posterior margin of the anus and postanal myomeres are those myomeres posterior to a vertical from the posterior margin of the anus; in many fishes the number of preanal and postanal myomeres approximate the number of precaudal (abdominal) and caudal vertebrae, respectively

Myoseptum / myosepta

thin partition of connective tissue which joins myomeres

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N

NL

notochord length (see also standard length - used as, prior to and during notochord flexion)

Nape

dorsal region of the body immediately behind the head

Nares

nostrils, openings leading to the olfactory organs; the openings of the nasal organs or rosettes

Narial

pertaining to the nares

Nasal

pertaining to region of the nostrils, or to the specific bone in that region

Nasal capsule

paired, more-or-less spherical structures on the snout that contain the olfactory organs

Natural hybrids

other species in the study area with which interbreeding has occurred naturally

Nekton

motile, marine organisms living in open water (rather than the sea floor) and capable of swimming against currents; small to moderate-sized nektonic organisms (e.g., midwater fishes, juvenile fishes, some cephalopods) are referred to as micronekton

Nephros

kidney; often used to refer to larval kidney

Neritic

pelagic coastal zone extending seaward to the margin of the continental shelf

Neural crest

region of the neural ridge of the developing embryo that differentiates into many kinds of tissue and cells, including melanophores

Neural spine

a median spine on the dorsal surface of a vertebral centrum, attached to the centrum by two bones that form an arch (neural arch) through which the spinal cord passes

Neustonic

inhabiting the surface of the ocean; plankton living in this zone are referred to as neuston

Notochord

longitudinal cartilaginous rod that supports the axis of the body; eventually replaced by the vertebral column in teleostean fishes

Notochord length (NL)

the distance from the tip of the snout to the posterior tip of the notochord; used prior to and during notochord flexion (see also: standard length)

Nuchal

referring to the region of the nape; immediately behind the head, dorsally

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O

Obtuse

with a blunt or rounded end; an angle greater than 90 degrees

Occipital crest

bony ridge located posteriorly on top of the head

Occipital region

area on dorsal surface of head, beginning above or immediately behind eyes and extending backwards to end of head

Occiput

see: occipital region

Oceanic

open sea zone seaward of the continental shelf or slope

Oil globule

discrete spheres of oil or fatty material within the yolk of some fish eggs

Olfactory buds

incipient olfactory organs

Ontogenetic characters

those characters associated with developmental stages

Ontogeny

developmental history of an organism from zygote to maturity

Opercle

upper posterior and usually largest bone of the gill cover of a fish; often used as synonym of operculum

Operculum

bony plate of the gill cover

Ophioblennium stage

pelagic stage of some salariin blenniids characterized by enlarged pectoral fins and enlarged, hooked teeth anteriorly in the lower jaw or in both jaws

Opisthonephros

the embryonic or larval kidney

Optic vesicles

embryonic vesicular structures which give rise to the eyes

Orbit

the bony socket of the eye

Organogenesis

the relatively advanced period of embryonic development characterized by formation of the organ systems

Origin (of fin)

anterior (usually) point of attachment of a fin

Ossification

process of bone formation involving calcification of cartilage or connective tissue

Otic

region of the head containing the auditory or hearing organs

Otoliths

small, calcareous, secreted bodies within the inner ear

Over yearling

fish having spent at least one winter in a stream; applies to trout and salmon

Oviparous

producing eggs that develop outside the maternal body

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P

P or P1

pectoral fin

P2 or V

pelvic fin

PAL

preanal length

PosAL

postanal length

PreAL

preanal length

PreDFL

predorsal fin length

PreDFFL

predorsal finfold length

Paedomorphic

referring to the phylogenetic retention of juvenile (or larval) characters in the adult stage

Palatine teeth

teeth on the paired palatine bones in the roof of the mouth of some fishes

Palatines

paired bones on the roof of the mouth, often bearing teeth

Papilla

a fleshy projection or protuberance

Parapatric

distribution of species or other taxa that meet in a very narrow zone of overlap

Paravertebral

along the same plane as the spinal column

Parhypural

lowermost supporting bone of the principal caudal fin rays

Parietal

paired bones of the roof of the skull

Parr marks

dark vertical oval bars along the sides, typical of salmonids

Pectoral (fin) bud

swelling at site of future pectoral fin; anlage of pectoral fin

Pectoral fin

paired lateral (sometimes ventrolateral) fins behind the head, articulating with the pectoral girdle

Pectoral fin base

supporting structure of the pectoral fin; in larvae it is peduncular and contains the muscles that operate the fin; its length is measured along the longitudinal axis from the point of insertion on the body to the point of attachment of the fin blade or rays; its depth is measured on the transverse axis at its widest (usually most distal) point

Pectoral fin length

distance from base to farthest tip of fin; prior to ray formation, pectoral fin length is measured from the base of the blade (finfold) to the greatest distal margin of the blade; after ray formation, pectoral fin length is measured from the point of insertion of the longest ray to the tip of the ray

Pedicel

a small, short stalk

Peduncle

fleshy end of the body between the anal and caudal fins; a narrow part or stalk that connects a structure to the body (e.g., caudal peduncle connecting caudal fin to body)

Pelagic

living in the open water habitat, as opposed to bottom living or inshore inhabitants; free-living in the sea away from the sea bottom, usually beyond the continental shelf; not necessarily near the surface

Pelvic bud

swelling at site of future pelvic (ventral) fins; anlage of pelvic fin

Pelvic fins

paired fins usually located ventrally on the body; various in position from beneath the head (jugular), to below the pectoral region (thoracic), to the gut region (abdominal); high on the sides in some stomioids; prior to ray formation, pelvic fin length is measured from the base of the blade (finfold) to the greatest distal margin of the blade; after ray formation pelvic fin length is measured from the point of insertion of the longest ray to the tip of the ray; articulating with the pelvic girdle; ventral fins

Periblast

thin membrane lying below the embryo and surrounding the yolk in teleosts; the space surrounding the yolk is invaded by nuclei, forming a syncytial region of unknown function; observed as a thin border around blastula

Pericardium

cavity in which the heart lies

Peritoneal

region of the body associated with the gut or the membrane of the peritoneum; often synonymous with perivisceral

Peritoneum

membranous lining of the abdominal cavity; the membrane and associated connective tissue lining the gut cavity

Perivitelline space

fluid-filled space between the embryo and shell or chorion and yolk material of an egg. Width of perivitelline space is the distance between yolk and egg capsule expressed either as direct measurement or a ratio of the egg diameter

Pharyngeal teeth

bony tooth-like projections derived from the fifth (

Pharyngeal) gill arch; teeth on the pharyngeal bones of the branchial skeleton

Photophores

luminous organs

Phylogenetic

referring to the evolutionary lineage of an organism

Physoclistic

having no connection between the esophagus and the pneumatic duct; typical of perciform fishes

Physostomous

having the swim bladder connected to the esophagus by the pneumatic duct

Plankton

small, free-living, weakly swimming or passively floating marine or fresh water organisms that drift with the currents

Plicae

wrinkle-like folds found on the lips of some catostomids

Post yolk-sac larva(e)

see: larva

Postanal

posterior to the anus

Postanal length (PosAL)

distance from the most posterior point of the anus to the most posterior point on the caudal fin or median finfold

Postanal myomeres

number of whole myomeres posterior to an imaginary vertical line at the most posterior point of the anus, including one urostylar element

Posterior

towards the back or caudal region; opposite to anterior

Postero-hyal

posterior bone to which branchiostegal rays attach, formerly epihyal

Postflexion larva

phase following upward flexion of the tip of the notochord (more precisely considered to begin with formation of all principal caudal fin rays) [note: for purposes of these keys, we do not make a distinction between pre- and post-flexion stages]

Postorbital

behind the eye or eye socket

Postorbital length

distance from posterior margin of eye to posterior edge of opercular membrane

Postorbital pores

pores in ascending canal behind eye, part of infraorbital canal series (eels)

Posttemporal spine

a spine that emerges from the posttemporal bone located on the posterolateral upper region of the skull

Preanal

located anterior to the anus

Preanal length (PAL or PreAL)

distance from the most anterior point on the snout to the most posterior point of the anus; synonymous with snout-anus distance

Preanal myomeres

number of myomeres from the nape to, and including any myomeres bisected by, an imaginary vertical line at the most posterior point of the anus

Preanal vertebrae

from the first vertebra to and including the vertebra intersected by a line drawn perpendicularly from the base of the first anal-fin ray (eels)

Prebranchial length

in petromyzontids, distance between the tip of the snout and the anterior margin of the first gill opening

Precaudal vertebrae

the anterior group of vertebrae that includes all centra anterior to the centrum with the first heamal spine

Precocious

specialized early formation of a structure (e.g., fins or fin elements) compared to typical developmental sequences in most fishes; does not infer abnormality

Predorsal length

distance from the most anterior point on the snout to the anterior margin of the base of the first dorsal fin ray when formed

Predorsal myomeres

number of myomeres from nape to dorsal origin of median finfold

Predorsal scales

scales along dorsal ridge from occiput to origin of dorsal fin

Predorsal vertebrae

from the first vertebra to and including the vertebra intersected by a line drawn perpendicularly from the base of the first dorsal-fin ray (eels)

Preflexion larva

phase between hatching and upward flexing of the tip of the notochord (or appearance of first caudal fin rays] [note: for purposes of these keys, we do not make a distinction between pre- and post-flexion stages]

Prejuvenile

developmental stage immediately following acquisition of minimum fin ray complement of adult and before assumption of adult-like body form; used only where strikingly different from juvenile

Premaxilla / premaxillae

primary bone of the upper jaw in most fish, usually bearing teeth; paired bones of the upper jaw anterior to the maxillae and usually bearing teeth; often protrusile, and extending ventrad of most of the maxillae in advanced teleosts

Premaxillary

the ventralmost of the two bones included in the upper jaw

Preopercle

upper anterior bone of the gill cover, often bearing serial spines; spines at the margin of the bone are referred to as posterior preopercular spines and those on a bony ridge forward of the margin are referred to as anterior preopercular spines

Preoperculomandibular pores

pores in preoperculomandibular canal, including mandibular pores along lower jaw and those in preopercular canal (both sometimes listed separately) (eels)

Preorbital

large bone anterior to the eye

Primordium

rudimentary form of an anatomical structure; anlage

Principle anal and dorsal fin rays

in certain fishes (e.g., Cyprinidae and Catostomidae), the principal rays include the branched rays plus one unbranched ray [the anteriorly adjacent, usually longest, unbranched ray]; the last two bases [branched rays, both of which articulate with the most posterior pterygiophore] are counted as one ray.

Principle caudal rays

caudal-fin rays originating on the hypural and parhypural elements; the number of principal rays is generally defined as the number of branched rays plus two.

Procurrent caudal rays

small dorsal and ventral rays of the caudal fin located anterior to the principal rays and not supported by hypural/parhypural elements

Pronephric ducts

ducts of pronephric kidney of early developmental stages

Protocercal tail

form with body axis extending through the caudal finfold

Protolarva

phase of larval development (used by Snyder et. al.) characterized by absence of dorsal, anal, and caudal fin spines and rays

Protractile

describing premaxillae which can be extended

Proximal

near the point of attachment or origin; opposite to distal

Psammophils

requiring sand as a substrate for spawning

Pterotic spines

spines emerging from the pterotic bone located posterior to the upper region of the orbit in the temporal region of the skull

Pterygoid

dermal bone of the upper jaw

Pterygiophore

bone of the anal internal skeleton supporting the dorsal and fins; cartilaginous or bony elements that form the fin base and support the fin rays of a fish

Punctate melanophore

round or dot-like melanophore

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Q

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R

Rays

segmented fin supports that are usually bilaterally paired and often branched

Redd

an excavated area or nest into which trout spawn

Reticulated

net-like or web-like in appearance

Retrorse

angled backward; usually referring to direction of a spine

River system

a group of streams or lakes which lead into a drainage (e.g., Fox

River system)

Rostrum

a prolongation of the snout, sometimes ending in a spine (rostral spine); rostrum length measured from the anterior edge of the upper jaw to the tip of the rostrum or spine (holocentrids)

Rudimentary fin rays

in certain fishes (e.g., Cyprinidae and Catostomidae), size-graded series of shorter, unbranched soft rays anterior to the principal rays of the dorsal, anal, and caudal fins; also called secondary rays or, in the case of the caudal fin, procurrent rays; In traditional texts, formulas are represented by lower case

Roman numerals

, e.g., iv instead of 4 and separated from the principal ray count in Arabic, by commas. These are not able to be displayed appropriately in an electronic key.

Rugose

having a wrinkled appearance; often used to describe bone with a highly textured surface; sometimes used to describe the appearance of the gut, caused by numerous mucosal folds

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S

SL

standard length

Sn-A

snout to anus

Saddle markings

pigment patterns which cover the dorsal and lateral aspects and give an overall appearance of a saddle

Sculptured

referring to an egg shell with ornamentation or surface features of various shapes and textures

Scute

a modified, thickened scale, often spiny or keeled

Secondary fin rays

see: rudimentary fin rays or procurrent rays

Segmented

particulate or divided; opposite of homogeneous in referring to egg yolk

Semibuoyant

referring to eggs which do not float nor sink, but remain suspended in the water column

Shell

the membrane that encloses an egg; generally, equivalent to chorion

Sigmoid heart

the

S-shaped heart which develops from the primitive heart tube

Snout

forward part of the head anterior to the eye; snout length measured in the longitudinal axis from the anteriormost pigmented surface of the eye to the tip of the snout

Snout-anus (Sn-A) (or snout-to-vent) length

distance from the tip of the snout to the posterior margin of the anus, measured at the longitudinal axis; equivalent to preanal length (PAL)

Snout to rictus (upper jaw)

tip of snout to angle of mouth

Soft rays

bilaterally paired, usually segmented, fin supports

Somites

primitive, segmented, mesodermal tissue along each side of notochord

Spatulate

having a rounded apex and tapering to a base; flattened or spoon-shaped

Spawning habitat

description of the environment in which spawning has been documented

Spawning season

months during which spawning has been documented for the Great Lakes region, unless otherwise stated

Spawning substrate

type of material upon which spawning is known to occur

Spawning temperature

water temperatures at which spawning has been documented

Speleophils

requiring cavities as a substrate for spawning

Sphenotic

bone at the upper part of the skull, often forming part of the orbit

Spines

supporting elements in the fins that are unsegmented, unpaired, unbranched, and usually (but not always) stiff, pungent and sharp (sometimes referred to as spinous rays); also, refers to pointed projections arising from various bones, usually on the head

Spinous rays

in certain otherwise soft-rayed fish, soft rays that during embryonic or larval development are thickened, fused, and hardened into spine-like structures, sometimes with moderate to strong serrations or barbs along their posterior margins. In formulas for fin-ray counts, fully spinous rays may be designated by Roman numerals like true spines.

Spinous scale

specialized larval scales with spines (not the serrated ctenoid scale of adult fishes)

Squamation

covering of scales

Stalked eye

eye borne on a stalk or peduncle

Standard length (SL)

distance from the most anterior point on the snout to the most posterior point of the notochord or hypural complex

Stellate melanophore

referring to a melanophore which is expanded into a star-like shape; the stellate condition can be temporary and the melanophore can become punctate after contraction

Stomodeum

primordial mouth; the anterior pitted portion of the embryonic gut

Striations

surface features in the form of lines or bands

Stripe

a horizontal band of pigment on the lateral surface of the head or body; sometimes occurring in a series

Subcutaneous

occurring beneath the skin

Submandibular

beneath the lower jaw; along the edge of the lower jaw

Subopercle

posterior bone of the gill cover lying below the opercle

Subterminal mouth

underneath or set back from the tip of the snout, sometimes referred to as an inferior mouth

Superior

spatial anatomical term meaning upper in position; opposite to inferior

Superior mouth

condition when the lower jaw extends upward and the mouth opens dorsally

Supracleithral spine

a spine originating from the supracleithrum located near the upper posterior margin of the head

Supramaxilla

small dermal bone attached posterior and dorsal to the maxilla

Supraoccipital spine

spine or crest on the midline of the back of the head originating from the supraoccipital bone

Supraoral

above the mouth; referring to the teeth of the oral disc in lampreys which are anterior to the mouth opening

Supraoral tooth plate

in petromyzontids, tooth plate immediately anterior to esophageal opening

Supraorbital pores

pores on dorsal surface of snout and head, including those in ethmoid canal at tip of snout (sometimes listed separately) and those on dorsal surface of snout and head; the posteriormost pores situated between the eyes are sometimes referred to as interorbital pores (eels)

Supratemporal pores total number of pores in supratemporal canal (usually including one median pore) (eels)

Swim bladder

gas-filled sac lying beneath the spinal column in the abdominal region (between the kidneys and alimentary canal in teleosts); also referred to as air bladder or gas bladder

Sympatric

species inhabiting the same or overlapping geographic areas

Syncytium

a multinucleate mass of protoplasm

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T

TL

total length

Tail

portion of the body posterior to the anus; the postanal region

Tail-bud stage

stage of embryonic development characterized by a prominent caudal bulge and marked development of cephalic region

Tail-free stage

stage of embryonic development characterized by separation of the tail from the yolk

Tail length

anus to tail tip; in petromyzontids, distance from cloacal slit to tip of caudal fin

Taxon / Taxa

taxonomic category or unit, as a species, genus, family, etc.

Teleosts

bony fishes

Telescopic eye

type of elongate, cylindrical eye that protrudes forward or upward within an envelope of skin

Temporal canal

connects the lateral line with the postorbital portion of the infraorbital canal; rarely contains pores (eels)

Terminal mouth

condition when lower and upper jaws are equal in length and the mouth opens terminally; type of mouth that opens anteriorly; typical of most fish larvae

Tesselated

markings or colors arranged into squares

Thoracic

pelvic region; referring to the chest area; usually the region of the body of a fish below the pectoral fin base

Total length (TL)

distance from the most anterior point on the snout to the most posterior point on the caudal fin or fin fold

Total vertebrae

total number of vertebrae including the first reduced vertebra and the hypural (eels)

Transformation

the process (synonymous with metamorphosis) at the end of the larval stage, characterized by a marked change in form or structure and involving acquisition of juvenile or adult characters and loss of larval characters; also refers to the stage where this process occurs; the term "transitional" is used sometimes for larvae that undergo a gradual transformation (e.g., in scombrids)

Truncate

ending abruptly along a vertical line

Trunk

portion of the body between the head and the anus; from posterodorsal point of gill opening to anus

Trunk length

in petromyzontids, distance between posterior margin of last gill opening and cloacal slit

Trunk myomeres

in petromyzontids, myomeres between the most posterior gill opening and the cloacal slit

Tubercle

small knobby protuberance

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U

Urohyal

a median bone in the throat region to which the sternohyoid muscles attach; not part of the hyoid arch

Urostyle

final vertebral segment usually modified for caudal fin support; complex bony structure (usually upturned) at the terminus of the vertebral column formed from the fusion of several vertebrae

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V

V [or P2]

central or pelvic fin

Vent

opening on the ventral surface of a fish where the alimentary and urinary canal open; essentially equivalent to the anus in larval fish

Ventral

lower part of the body; opposite to dorsal

Ventral fins

pelvic fins; paired fins articulating with the pelvic girdle

Ventrum

lowermost part of the body; ventral body margin; opposite to dorsum

Vermiculate

having worm-like markings

Vestigial

part of the body that once had a function but has become functionless in the course of evolution

Vertebral formula

expressed as the range of counts of predorsal, preanal, and total vertebrae (eels)

Vertical blood vessel

one or more of the vertically oriented blood vessels connecting the aorta with the gut or kidney in leptocephali

Vexillifer stage

larval stage of caraphids characterized by the tentacle-like dorsal fin ray

Vexillum

highly modified elongate anterior dorsal-fin ray in larval carapids

Villiform

in the form of finger-like projections

Vitelline membrane

after water hardening, the membrane surrounding the egg proper (animal and vegetal material)

Vitelline vessels

arteries and veins of yolk region

Viviparous

type of reproduction where the embryos develop within the ovary and receive maternal nutrition; live-bearing

Vomer

anterior, median bone of the roof of the mouth/palate (=prevomer)

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W

Water hardening

process of membrane delamination and fluid formation which forms the perivitelline space bordered by the chorion and vitelline membrane; expansion and toughening of egg capsule due to absorption of water into the perivitelline space

Weberian vertebrae

first four vertebrae in cyprinids, catostomids, and ictalurids which are modified to connect the swim bladder to the inner ear

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X

Xanthophores

chromatophores bearing yellow pigment

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Y

YSD

yolk-sac depth

YSL

yolk-sac larva(e) or yolk-sac length

Yearling

a fish in its second year

Yolk

nutritive material of the egg or in a sac-like mass (yolk sac) below the abdominal region of a newly hatched larva; usually seen as a yellowish sphere diminishing in size as development proceeds

Yolk diameter

greatest diameter of yolk; more accurately measurable prior to embryo formation

Yolk plug

yolk within the blastopore

Yolk sac

a bag-like ventral extension of the primitive gut containing the yolk

Yolk-sac larvae (YSL)

phase of development from the moment of hatching to complete absorption of yolk; early larval stage with yolk present in a sac-like region of the gut

Yolk-sac length (YSL)

horizontal distance from most anterior to most posterior portion of yolk-sac

Yolk-sac depth

vertical distance from dorsum to venter of yolk sac

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Z