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)  View example
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)  View example
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)  View example
axillary processan enlarged and pointed scale located at the base of the pelvic fin in the family Salmonidae (Chinook salmon-A)  View example
bara generally rectangular-shaped and vertically oriented area of pigment on the side or fins of a fish (banded darter-A; logperch-B)  View example
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)  View example
base (of fin)the length of a fin where it is attached to the body (black crappie-A)  View example
body depth the greatest straight-line height or depth of the body, from the dorsal to the ventral surface (black buffalo-A)  View example
body width the greatest straight-line distance from one side to the other (sauger-A,B)  View example
branchial referring to the gills and the area they occupy (e.g., branchial cavity), often also including the throat (mud darter-A)  View example
branchiostegal raysthin 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)  View example
breast the ventral surface of the body between the gill covers and the pelvic fins, just posterior to the throat (blackchin shiner-A)  View example
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)  View example
caudal finthe tail (northern pike-A; freshwater drum-B)  View example
caudal pedunclethe portion of the body between the posterior end of the anal fin base and the caudal base (brook stickleback-A)  View example
caudal peduncle depththe greatest depth (straight-line distance from dorsal to ventral surface) of the caudal peduncle (mottled sculpin-A)  View example
caudal peduncle lengththe straight-line distance from the posterior end of the anal fin base to the caudal base (slimy sculpin-A)  View example
caudal peduncle scalesthe number of scale rows completely encircling the caudal peduncle (greater redhorse-A)  View example
cheekthe portion of the head between the eye and the posterior edge of the preopercle (northern pike-A; rainbow darter-B)  View example
circumferential scalesthe number of scale rows completely encircling the body just anterior to the origin of the dorsal fin (shortnose gar-A; largescale stoneroller-B)  View example
circumoral teethrows of teeth radiating laterally from the mouth of post-larval lampreys (Petromyzontidae) (chestnut lamprey-A; northern brook lamprey-B)  View example
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)  View example
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)  View example
dorsalpertaining to the top of the fish (shortnose gar-A; yellow perch-B)  View example
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)  View example
dorso-ventrally flatteneda 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)  View example
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)  View example
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)  View example
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)  View example
ganoid scalesThick inflexible rhomboid-shaped scales characteristic of gars (Lepisosteidae) (shortnose gar-A)  View example
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)  View example
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)  View example
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)  View example
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)  View example
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)  View example
gular plate a flat bone in the middle of lower jaw of certain fishes of ancient origin, most conspicuously the bowfin (Amiidae) (bowfin-A)  View example
inferior moutha mouth located on the ventral surface of the head and oriented downwards (white sucker-A; shovelnose sturgeon-B)  View example
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)  View example
insertion (of a fin)the posterior-most point where the fin connects with the body; see also the origin of the fin (mooneye-A)  View example
intromittent organa 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)  View example
isthmusa 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)  View example
keela 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)  View example
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)  View example
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)  View example
laterally compresseda body shape in which the body depth is more than three times the body width (bluegill-A; golden shiner-B)  View example
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)  View example
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)  View example
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)  View example
nipple a small, rounded projection from the center of the lower lip in some carpsucker species (Carpiodes, Catostomidae) (river carpsucker-A)  View example
obliquereferring 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)  View example
operclethe largest and posterior-most of the bony plates that make up the gill covers (muskellunge-A; paddlefish-B)  View example
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)  View example
orbitthe opening in the skull which contains the eye (kiyi-A)  View example
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)  View example
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)  View example
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)  View example
parr marksOval bars on the sides of juveniles (parr) of some species of the Salmonidae (brown trout-A; chinook salmon-B)  View example
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)  View example
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)  View example
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)  View example
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)  View example
post-orbital distancethe straight-line distance from the posterior end of the orbit to the posterior-most end of the opercle (mottled sculpin-A)  View example
pre-dorsal scalesthe 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)  View example
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)  View example
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)  View example
protractilerefers 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)  View example
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)  View example
ray a segmented flexible support element of the fins, often branched at the tip (see also spine) (quillback-A; Mississippi silvery minnow-B)  View example
saddlesrectangular blotches of dark pigment extending from the sides over the dorsal surface (rainbow darter-A; northern hog sucker-B)  View example
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)  View example
spine (of preopercle) a rigid, pointed, bony process extending from the posterior edge of the preopercle (ruffe-A; deepwater sculpin-B)  View example
spiraclean 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)  View example
standard lengththe straight-line distance from the anterior tip of the snout to the caudal base (black buffalo-A)  View example
stripea horizontal line of pigment along the side or fins (fantail darter-A; hornyhead chub-B)  View example
subterminal moutha 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)  View example
superior moutha mouth oriented dorsally in which the angle of the mouth with the horizontal is greater than 60 degrees (pugnose minnow-A; banded killifish-B)  View example
supraoral lamina teetha 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)  View example
terminal moutha 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)  View example
throatthe area of the ventral surface below the branchial cavity and just anterior to the breast that includes the isthmus (mud darter-A)  View example
total lengththe straight-line distance from the anterior tip of the snout to the posterior tip of the caudal fin (southern brook lamprey-A; muskellunge-B)  View example
transverse scalesthe 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)  View example
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)  View example
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)  View example
ventralpertaining to the underside or bottom of the fish (burbot-A; freshwater drum-B)  View example
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)  View example