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Fish Glossary

adipose fin

a small fleshy fin, lacking rays or spines, located on the midline of the dorsal surface between the dorsal fin and caudal fin. In Wisconsin the families Ictaluridae, Salmonidae, Osmeridae, and Percopsidae have adipose fins. Usually independent of other fins (troutperch-A; coho salmon-B), but attached to the caudal fin in the madtoms (Noturus, Ictaluridae) (stonecat-C)
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ammocoete

the larval life stage of the lamprey (Petromyzontidae) characterized by a lack of eyes and a fleshy hood and sieve apparatus covering the mouth (American brook lamprey-A; chestnut lamprey-B,C)
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anal fin

a single, unpaired fin located along the midline of ventral surface between the vent and caudal fin. The anal fin may have spines and rays (rock bass-A; brook stickleback-B) or just rays (common shiner-C; black bullhead-D)
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axillary process

an enlarged and pointed scale located at the base of the pelvic fin in the family Salmonidae (Chinook salmon-A)
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bar

a generally rectangular-shaped and vertically oriented area of pigment on the side or fins of a fish (banded darter-A; logperch-B)
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barbel

a fleshy and flexible process, usually covered with taste buds, found near the mouth. In Wisconsin the families Ictaluridae, Gadidae, and some members of the Cyprinidae have barbels (black bullhead-A; burbot-B; common carp-C; speckled chub-D)
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base (of fin)

the length of a fin where it is attached to the body (black crappie-A)
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branchial

referring to the gills and the area they occupy (e.g., branchial cavity), often also including the throat (mud darter-A)
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branchiostegal rays

thin bones located just posterior and ventral to the gill covers that support the gill membranes. The number of branchiostegal rays is useful for distinguishing certain species of Salmonidae and Esocidae (rainbow trout-A; muskellunge-B)
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body depth

the greatest straight-line height or depth of the body, from the dorsal to the ventral surface (black buffalo-A)
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body width

the greatest straight-line distance from one side to the other (sauger-A,B)
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breast

the ventral surface of the body between the gill covers and the pelvic fins, just posterior to the throat (blackchin shiner-A)
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caudal base

the base of the caudal fin (tail) where the vertebral column ends (the posterior end of the hypural plate), which can be seen as a crease in the skin when the tail is flexed from side to side (ninespine stickleback-A)
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caudal fin

the tail (northern pike-A; freshwater drum-B)
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caudal peduncle

the portion of the body between the posterior end of the anal fin base and the caudal base (brook stickleback-A)
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caudal peduncle depth

the greatest depth (straight-line distance from dorsal to ventral surface) of the caudal peduncle (mottled sculpin-A)
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caudal peduncle length

the straight-line distance from the posterior end of the anal fin base to the caudal base (slimy sculpin-A)
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caudal peduncle scales

the number of scale rows completely encircling the caudal peduncle (greater redhorse-A)
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cheek

the portion of the head between the eye and the posterior edge of the preopercle (northern pike-A; rainbow darter-B)
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circumoral teeth

rows of teeth radiating laterally from the mouth of post-larval lampreys (Petromyzontidae) (chestnut lamprey-A; northern brook lamprey-B)
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circumferential scales

the number of scale rows completely encircling the body just anterior to the origin of the dorsal fin (shortnose gar-A; largescale stoneroller-B)
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ctenoid

scales that have small teeth (ctenii) on their exposed posterior margins and which give the side of a fish a rough feel. In Wisconsin the families Percopsidae (ctenii weakly developed), Apredoderidae, Moronidae, Centrarchidae, Percidae, Sciaenidae, and Gobiidae have ctenoid scales (troutperch-A; yellow perch-B)
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cycloid

scales that lack small teeth on their exposed posterior margins and which give the side of a fish a relatively smooth feel. In Wisconsin the families Hiodontidae, Anguillidae, Clupeidae, Cyprinidae, Catostomidae, Esocidae, Umbridae, Salmonidae, Osmeridae, Gadidae, Fundulidae, and Atherinopsidae have cycloid scales (golden shiner-A; golden redhorse-B), and the family Amiidae (bowfin) has somewhat different but cycloid-like scales (bowfin-C)
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dorsal

pertaining to the top of the fish (shortnose gar-A; yellow perch-B)
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dorsal fin

an unpaired fin located along the midline of the dorsal surface. It may have both spines and rays or just rays and consist of a single lobe (creek chub-A), two lobes that are joined (smallmouth bass-B) or separate (brook silverside-C), or a series of free spines and a lobe with rays (threespine stickleback-D)
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dorso-ventrally flattened

a body shape in which the body width is clearly greater than the body depth and the fish looks as if it has been flattened from above (flathead catfish-A)
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falcate

a fin shape, usually only noted in the dorsal fin or anal fin, in which the anterior few rays are noticeably and somewhat abruptly longer than subsequent rays, giving the edge of the fin a strongly curved (sickle-shaped) or concave profile (blue sucker-A; coho salmon-B)
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frenum

a bridge of tissue connected the upper jaw with the upper lip, which are otherwise separated by a groove (blacknose dace-A; rainbow darter-B)
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fusiform

a more-or-less evenly proportioned body shape that in side view displays a regular and gradually tapered increase from the snout to the deepest area in mid body and then a regular and gradually tapered decrease to the tail. The standard length is about three to four times the body depth, and the body depth is about two to three times the body width (rainbow trout-A; largemouth bass-B)
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ganoid scales

Thick inflexible rhomboid-shaped scales characteristic of gars (Lepisosteidae) (shortnose gar-A)
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gill arches

bony or cartilaginous arches that support the gills, located on both sides of the branchial cavity, arranged in overlapping layers, and covered by the gill covers. The anterior-most arch is termed the first gill arch (skipjack herring-A)
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gill covers

the flat bony plates that cover the branchial cavity and gills, consisting of the preopercle, interopercle, subopercle, and opercle (lake whitefish-A; paddlefish-B)
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gill membranes

flexible membranes connecting the branchiostegal rays to each other and to the opercle. The gill membranes also connect the gill cover and branchiostegal rays from one side of the head with those of the other across the throat region. The gill membranes provide the seal that allows the movement of the gill cover and branchiostegal rays to pump water over the gills. Where the gill membrane connection across the throat is limited to the anterior area, the gill covers are said to be narrowly connected (rainbow darter-A), and where the connection extends to the posterior area the gill covers are said to be boradly connected (banded darter-B)
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gill rakers

knobby or comb-like cartilaginous filaments extending anteriorly and inward from the gill arches. Used to sieve small food items from water passing over the gills. The shape, size, and number of gill rakers on the first gill arch is useful for distinguishing among many Wisconsin species (cisco/lake herring-A; lake whitefish-B; pumpkinseed-C)
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gonopodium

modified anal fin of males in the family Poeciliidae to facilitate copulation and internal fertilization; more generally, the gonopodium is a type of intromittent organ (western mosquitofish-A)
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gular plate

a flat bone in the middle of lower jaw of certain fishes of ancient origin, most conspicuously the bowfin (Amiidae) (bowfin-A)
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inferior mouth

a mouth located on the ventral surface of the head and oriented downwards (white sucker-A; shovelnose sturgeon-B)
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infraorbital canal

the portion of the lateral line sensory system on the head that begins behind the eye, curves under the eye, and the continues on to the snout; interrupted or incomplete in some species (ghost shiner-A)
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insertion (of a fin)

the posterior-most point where the fin connects with the body; see also the origin of the fin (mooneye-A)
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isthmus

a narrow bridge of bone (or cartilage) found underneath the branchial cavity that supports the gill arches and connects the body to the head. In some species largely covered by the gill membranes (paddlefish-A; fantail darter-B)
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intromittent organ

a structure on a male fish that helps in internal fertilization of the female; the intromittent organ of the Poeciliidae is termed a gonopodium (western mosquitofish-A)
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keel

a relatively narrow and sharp ridge-like area of the ventral or dorsal surfaces or the sides of the caudal peduncle (goldeye-A; ninespine stickleback-B)
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lateral line

a fluid-filled sensory canal running along each side of many species (and extending on the head as well û see infraorbital canal and mandibular pores). The canal has numerous openings or pores, and the number of scales along the side with these pores (one pore per scale) between the posterior end of the opercle and the caudal base is the lateral line scale count (lake whitefish-A; bluegill-B)
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lateral series

in species where the lateral line is incomplete or lacking along the sides, the number of scale rows along the middle of the side between the posterior end of the opercle and the caudal base (spotted sucker-A; Iowa darter-B)
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laterally compressed

a body shape in which the body depth is more than three times the body width (bluegill-A; golden shiner-B)
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mandibular pores

sensory pores located on the underside of the lower jaw (mandible or chin) that are part of the lateral line sensory system, the number of which is useful in identification of the Wisconsin families Esocidae, Salmonidae, and Cottidae (grass pickerel-A; spoonhead sculpin-B)
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melanophores

tiny, irregular blotches (dot-like) of dark pigment found on the skin and fins. Melanophore patterns are particularly useful for distinguishing among certain of the Cyprinidae (sand shiner-A; spotfin shiner-B)
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myomere

distinct muscle segments along the sides, visible through the skin and used in the identification of the lampreys (Petromyzontidae) (sea lamprey-A; silver lamprey-B)
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nipple

a small, rounded projection from the center of the lower lip in some carpsucker species (Carpiodes, Catostomidae) (river carpsucker-A)
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oblique

referring to the angle that a terminal or subterminal mouth makes with the horizontal axis of the head; oblique indicates greater than 0 degrees but less than 60 degrees. Angles between 30 degrees and 60 degrees are often termed "strongly oblique". For angles greater than 60 degrees the mouth is usually considered superior. (blackchin shiner-A; channel shiner-B)
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opercle

the largest and posterior-most of the bony plates that make up the gill covers (muskellunge-A; paddlefish-B)
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operclular tab (or flap)

a rounded, fleshy or cartilaginous extension of the upper posterior portion of the opercle, the color, size, and flexibility of which is important in the identification of certain of the sunfishes (Lepomis, Centrarchidae) (bluegill-A; longear sunfish-B)
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orbit

the opening in the skull which contains the eye (kiyi-A)
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origin (of a fin)

the anterior-most point where the fin connects with the body; see also the insertion of the fin (gizzard shad-A)
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palatine teeth

patches of small teeth on the palatine bones that are found on each side of the roof of the mouth, flanking the vomer, and that are useful in the identification of the Salmonidae and Cottidae (brown trout-A; mottled sculpin-B)
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papillae (adjective papillose)

small, fleshy, rounded protuberances, often on the lips, that are useful in the identification of the Acipenseridae and Catostomidae (see also plicae) (silver redhorse-A; shovelnose sturgeon-B)
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parr marks

Oval bars on the sides of juveniles (parr) of some species of the Salmonidae (brown trout-A; chinook salmon-B)
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pectoral fins

paired fins located on the side or ventral surface just posterior to the gill covers that may have spines and rays or just rays (yellow bullhead-A, black crappie-B)
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pelvic fins

paired fins (absent in Anguillidae) located on the ventral surface either just anterior to the vent (abdominal; bloater-A), underneath the pectoral fins (thoracic; freshwater drum-B), or just posterior to the isthmus in the throat (jugular; burbot-C). They may have spines and rays or just rays (slimy sculpin-D)
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peritoneum

the membrane lining the body cavity, the pigmentation of which is useful in identifying many of the minnows (Cyprinidae) (northern redbelly dace-A; bullhead minnow-B)
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plicae (adjective plicate)

fleshy areas arranged into folds or ridges with grooves between them, usually used in reference to the lips of the suckers (Catostomidae) (golden redhorse-A; greater redhorse-B)
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post-orbital distance

the straight-line distance from the posterior end of the orbit to the posterior-most end of the opercle (mottled sculpin-A)
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pre-dorsal scales

the number of scales on the dorsal surface between the posterior end of the head and the origin/insertion of the dorsal fin (striped shiner-A)
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preopercle

the anterior-most of the bony plates that make up the gill cover, sometimes with spines on its edge (smallmouth buffalo-A; ruffe-B; deepwater sculpin-C)
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protractile

refers to lips that can be extended or thrust out from the jaw and that are not rigidly connected to the upper jaw by a frenum (white crappie-A; river shiner-B)
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prickles

tiny, bony points on the skin of the Cottidae, the evolutionary remnants of scales, that give the skin a rough, sandpaper-like feel (spoonhead sculpin-A)
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pyloric caeca (singular caecum)

finger-like sacs attached to the posterior end of the stomach where it joins with the intestine, the number and size of which are useful in identifying some of the Salmonidae and Percidae (lake trout-A; sauger-B)
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ray

a segmented flexible support element of the fins, often branched at the tip (see also spine) (quillback-A; Mississippi silvery minnow-B)
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saddles

rectangular blotches of dark pigment extending from the sides over the dorsal surface (rainbow darter-A; northern hog sucker-B)
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spine (of a fin)

an un-segmented, rigid, support element of the fins, pointed at the tip (yellow bass-A, brook stickleback-B). In common carp and goldfish (Cyprinidae) and in the Ictaluridae several of the anterior rays of the dorsal, anal, and/or pectoral fins are fused together to form a segmented but rigid pointed spine, also known as a spinous or spiny ray (common carp-C; brown bullhead-D)
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spine (of preopercle)

a rigid, pointed, bony process extending from the posterior edge of the preopercle (ruffe-A; deepwater sculpin-B)
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spiracle

an opening on the head behind the eye that connects with the branchial cavity. In Wisconsin fishes found only in the paddlefish (Polyodontidae) and lake sturgeon (Acipenseridae) (paddlefish-A; lake sturgeon-B)
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standard length

the straight-line distance from the anterior tip of the snout to the caudal base (black buffalo-A)
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stripe

a horizontal line of pigment along the side or fins (fantail darter-A; hornyhead chub-B)
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subterminal mouth

a mouth oriented and opening primarily forward but also somewhat ventrally in which the upper jaw and snout clearly extend beyond the lower jaw (bluntnose minnow-A; banded darter-B)
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superior mouth

a mouth oriented dorsally in which the angle of the mouth with the horizontal is greater than 60 degrees (pugnose minnow-A; banded killifish-B)
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supraoral lamina teeth

a row of two or more tooth cusps on a single base located just above the mouth in post-larval lampreys (Petromyzontidae) (American brook lamprey-A; sea lamprey-B)
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terminal mouth

a mouth opening at the anterior tip of the head in which the upper and lower jaws are approximately the same length with neither one extending beyond the other. The orientation of the mouth may be either horizontal or oblique (emerald shiner-A; walleye-B)
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throat

the area of the ventral surface below the branchial cavity and just anterior to the breast that includes the isthmus (mud darter-A)
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total length

the straight-line distance from the anterior tip of the snout to the posterior tip of the caudal fin (southern brook lamprey-A; muskellunge-B)
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transverse scales

the number of scale rows in a vertical-oblique direction from the mid-ventral scale row just anterior to the vent to the mid-dorsal scale row; useful in distinguishing among the gars (Lepisosteidae) (spotted gar-A)
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tubercle

a calcified and hard protuberance, often pointed, found on the head, scales, and/or fins of breeding individuals, particularly in the families Cyprinidae and Catostomidae (hornyhead chub-A; blue sucker-B, C)
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vent

the opening, located on the ventral surface, that contains the anus, through which wastes are expelled, and genital pore, through which gametes are released. Usually found just anterior to the anal fin, but in adult pirate perch (Aphredoderidae) found in the throat region anterior to the pelvic fins (silver redhorse-A; sea lamprey-B; pirate perch-C)
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ventral

pertaining to the underside or bottom of the fish (burbot-A; freshwater drum-B)
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vomerine teeth

teeth on the vomer bone, found along the midline of the roof of the mouth, useful in the identification of some of the Salmonidae (brown trout-A; Atlantic salmon-B)
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