Fish Family Key


This is a dichotomous key. Compare the two descriptions for each couplet, starting with couplet 1, to see which best fits the fish you are identifying. Then click on your choice under "Goto" to go to another couplet until you've identified the fish's family.

CoupletCharactersGotoPicsOther Families
(not represented)
  1a One or two fleshy dorsal fins with no rays; 5 or more pairs of lateral gill slits; teeth set in set in numerous transverse rows. (Sharks) 2  
  1b Without 5 or more pairs of lateral gill slits (usually 1 pair lateral or several pairs ventral). 8  
  2a Head flattened, extended laterally, eyes on the end of extensions Sphyrnidae - hammerheads  
  2b Head not as above, rounded snout 3  
  3a Eyes behind mouth. 4  
  3b Eyes over or in front of mouth. 5  
  4a Barbels on nostrils, tail fin with slightly extended lower lobe Ginglymostomatidae - nurse sharks  
  4b No barbels on nostrils, tail fin with 2 well developed lobes Rhincodontidae - whale sharks  
  5a Spines at origin of both dorsal fins; anal fin absent Squalidae - spiny dogfish sharks  
  5b No spines on dorsal fins; anal fin present 6  
  6a Eyes small and/or narrow, oblong, cat-like; precaudal pit absent. Triakidae - houndsharks  
  6b Eyes round; precaudal pit present or absent. 7  
  7a One dorsal fin; 6-7 lateral gill slits; precaudal pit absent. Hexanchidae - cow sharks  
  7b Two dorsal fins; 5 lateral gill slit; precaudal pit presnt. Carcharhinidae - requiem sharks Lamnidae (mackerel sharks), Alopiidae (thresher sharks), Odontaspididae (sand tigers), Squatinidae (angel sharks, no precaudal pit)
  8a Body flattened dorsoventrally with eyes above or lateral with mouth and 5 pair of gill slits on ventral surface (rays). 9  
  8b Body not as above 13  
  9a Eyes on sides of head; head distinct from body or forming lobes. Rhinopteridae - eagle rays  
  9b Eyes on top of head; head not distinct from body. 10  
  10a Body disc more than 1.5 times wider than long; tail shorter than disc. Gymnuridae - butterfly rays  
  10b Body disc less than 1.5 times as wide than long; tail as long or longer than disc. 11  
  11a Tail with no dorsal fins; tail with 1 or more strong serrated spines. Dasyatidae - stingrays  
  11b Tail with 2 dorsal fins near tip; no single strong tail spine. 12  
  12a Disk rhomboidal heart-shaped; tail separate from disk; thorns on dorsal surface (Rajidae only). Rajidae - skates Pristidae (sawfishes), Rhinobatidae (guitarfishes)
  12b Disk (head and pectoral fins) circular to ovate; tail attached to disk; no thorns on dorsal surface. Narcinidae - numbfishes Torpedinidae (electric rays)
  13a Body laterally compressed with both eyes on the same side (flounder-like). 14  
  13b Body not as above. 17  
  14a Caudal fin continuous with dorsal and anal fin. Cynoglossidae - tonguefishes  
  14b Caudal fin distinctly separate from the dorsal and anal fins. 15  
  15a Preopercle margin covered with skin and scales; eyes on the right side of head. Achiridae - soles  
  15b Preopercle margin free, not covered with skin and scales; both eyes on the left or right side of head. 16  
  16a Pelvic fin bases short and nearly symmetrical. Paralichthyidae - sand flounders  
  16b Pelvic fin bases long (or long on ocular side and short on blind side) and are moderately to strongly asymmetrical. Bothidae - left-eyed flounders  
  17a Pelvic fins absent. 18  
  17b Pelvic fins present. Rays may separated, filamentous, long or short. 26  
  18a Body very elongate, flattened laterally; no caudal fin rays, tail tapers to a point. Silvery. Trichiuridae - cutlassfishes Carapidae (pearlfishes)
  18b Body not as above. 19  
  19a Body very elongate and snake or eel-like. Posterior nostril on or slightly above upper lip. 20  
  19b Body not snake-like or if snake-like. 21  
  20a Posterior nostril on or slightly above upper lip. Ophichthidae - shrimp eels Moringuidae (spagetti eels), Nettastomatidae (duckbill eels), Congridae (conger eels) and Synaphobranchidae (cutthroat eels).
  20b Posterior nostril is above or beside eye, well above lips. Head with elevated slope. Muraenidae - moray eels  
  21a Snout tubular; body covered with hard bony plates Syngnathidae - pipefishes  
  21b Snout not as above 22  
  22a 2 dorsal fins. 1st is made of 2-3 spines (last spine may be minute. Skin rough to the touch. 23  
  22b 1 dorsal fin with no spines. 24  
  23a 3 dorsal fin spines. Balistidae - triggerfishes  
  23b 2 dorsal fin spines, second one minute. Monacanthidae - filefishes  
  24a Teeth plate-like in each jaw, plates divided or single 25  
  24b Teeth not plate-like Stromateidae - butterfishes Xiphiidae (swordfishes), Ostraciidae (trunkfishes)
  25a 2 plate-like teeth in each jaw. Body smooth or prickly. Tetraodontidae - puffers  
  25b 1 plate-like tooth in each jaw. Body covered with spines (or leathery and thick-Molidae). Diodontidae - porcupinfishes Molidae (ocean sunfishes)
  26a Adipose fin present 27  
  26b No adipose fin. 31  
  27a Barbels present on lips or chin. 28  
  27b No barbels on chin. 29  
  28a 4 pair of barbels on chin (1 pair on nostrils, 1 on lip, 2 on chin). Ictaluridae - North American catfishes  
  28b 2 or 3 pair of barbels on chin and upper lip Ariidae - sea catfishes  
  29a Body deep, laterally compressed. Characidae - pacus  
  29b Body long and narrow. 30  
  30a Snout pointed. Mouth extends well past the eye. Synodontidae - lizardfishes  
  30b Snout rounded. Mouth extends to near posterior end of eye. Aulopidae - flagfins  
  31a Pelvic fins abdominal, well behind pectoral fins. 32  
  31b Pelvic fins below or anterior to pectoral fins. Rays may be separate, filamentous, long or short. 49  
  32a 1 dorsal fin. 33  
  32b 2 dorsal fins. 46  
  33a Snout extended into a toothy beak. Body covered by thick, tough scales (or bony plates as in Acipenseridae - sturgeons). Lepisosteidae - gars Acipenseridae (sturgeons)
  33b Snout, if extended, not as above. No thick, tough scales. 34  
  34a 1 or both jaws extended into needle-like mouth. 35  
  34b Jaws not needle-like. 36  
  35a Only lower jaw extended. Hemiramphidae - halfbeaks  
  35b Both jaws extended. Belonidae - needlefishes  
  36a Pectoral fins elongate, reaching almost to tail. Exocoetidae - flyingfishes  
  36b Pectoral fins not elongate. 37  
  37a Top of head naked, no scales. 38  
  37b Top of head wholly or partly with scales. 44  
  38a Gular plate present. 39  
  38b Gular plate absent. 40  
  39a Last ray of dorsal fin elongate. Megalopidae (tarpons)  
  39b Last ray of dorsal fin not elongate Elopidae - tenpounders  
  40a Snout extends past lower jaw. Engraulidae - anchovies Albulidae (bonefish)
  40b Snout approximately even with lower jaw. 41  
  41a Lower jaw covered by upper jaw when mouth closed or snout rounded with subterminal mouth; most with serrated keel on belly. Clupeidae - herrings  
  41b Jaws not as above; no keeled belly. 42  
  42a Long tubular snout with small mouth at end. Fistulariidae - cornetfishes  
  42b Mouth not extended, not tubular. 43  
  43a Lips thick and mouth inferior (except in bigmouth buffalo-lips thin, mouth oblique, terminal) Catostomidae - suckers  
  43b Lips thin; mouth slightly subterminal with upper jaw slightly protruding past lower jaw. Cyprinidae - carps  
  44a Dorsal fin with 7-8 rays. Anal fin with <10 rays. 3rd anal ray not branched. Poeciliidae - livebearers  
  44b Dorsal fin wit 9 or more rays. Anal fin with 12 or more rays. 3rd anal ray branched. 45  
  45a Teeth conical; body elongate and slender (except diamond killifish, the adults of which have a deeper body with alternating dark and light vertical stripes). Fundulidae - killifishes  
  45b Teeth tricuspid; body deep with irregular dark, vertical markings on side. Cyprinodontidae - pupfishes  
  46a Pectoral fin with lower rays separate, filamentous. Polynemidae - threadfins  
  46b Pectoral fin with all rays held together by membrane. 47  
  47a Mouth large with large sharp teeth. Lower jaw projecting past upper jaw. Sphyraenidae - barracudas  
  47b Mouth small. 48 Aulostomidae (trumpetfishes)
  48a Lateral silvery stripe down side. 1 spine in anal fin. Atherinopsidae - silversides  
  48b No lateral stripe. 2-3 spines in anal fin. Mugilidae - mullets  
  49a Gill openings behind pectoral fins 50  
  49b Gill openings in front of pectoral fins. 51  
  50a Gill openings behind or in upper pectoral axil Ogcocephalidae - batfishes  
  50b Gill openings in or behind lower pectoral axil Antennariidae - frogfishes  
  51a Pelvic fins joined together at breast to form 1 fin Gobiidae - gobies  
  51b Pelvic fins separate. 52  
  52a Body completely scaleless. 53  
  52b Body at least partially covered with scales or bony plates, though they may be small and hard to see (as in mackerels and jacks). 55  
  53a Sucking disc on breast. Gobiesocidae - clingfishes  
  53b No sucking disk on breast. 54  
  54a Head broad, dorsoventrally flattened; eyes on top of head. Batrachoididae - toadfishes  
  54b Head flattened more laterally; eyes high on sides of head. Blenniidae - blennies Chaenopsidae (tube blennies)
  55a Dorsal and anal fin rays continuous with caudal fin rays. Ophidiidae - cusk-eels Steindachneriidae (luminous hakes)
  55b Dorsal and anal fins separate from caudal fin 56  
  56a Bony longitudinal ridge below eye, sometimes with spines. 57  
  56b No bony longitudinal ridge below eye. 58  
  57a Lower part of pectoral fin with separated rays. Triglidae - searobins  
  57b All pectoral rays attached to each other. Scorpaenidae - scorpionfishes  
  58a Sucking disk on top of head. Echeneidae - remoras  
  58b No sucking disk on top of head. 59  
  59a Anal fin preceding by 2 free spines in small fish and some adults; scales small to minute; caudal peduncle very slender; some fish with keel (modified raised scales) on lateral line and caudal peduncle. Carangidae - jacks  
  59b Anal fin not preceded by 2 free spines; no keel on caudal peduncle or if keel present, body scales are large. 60  
  60a Dorsal spines all or nearly all disconnected from each other. 61  
  60b All (except possibly 1st 2) dorsal spines, if present, connected by membranes. 62  
  61a Body elongate, torpedo-shaped. Rachycentridae - cobias  
  61b Body ovate, laterally compressed. Ephippidae - spadefishes  
  62a Dorsal and anal fins followed by more than one detached finlets. Scombridae - mackerels/tunas Gempylidae (snake makerels and escolars)
  62b No finlets or no more than 1 finlet behind fins. 63  
  63a Throat with 2 long barbels. Mullidae - goatfishes  
  63b Throat without barbels. 64  
  64a Nostrils single on each side of head. Pomacentridae - damselfishes  
  64b Nostrils double on each side of head. 65  
  65a Lateral line extends to or nearly to tip of caudal fin. 66  
  65b Lateral line does not extend onto caudal fin. 68  
  66a 1 or 2 anal spines. Sciaenidae - drums  
  66b 3 anal spines. 67  
  67a Head slightly concave in profile; 2nd anal spine strongest and longest; no spines on operculum. Centropomidae - snooks  
  67b Head profile not concave; 3rd anal spine longest; 1 or 2 flat spines on operculum. Moronidae - temperate basses  
  68a Mouth nearly vertical; eyes on top of head. Uranoscopidae - stargazers Dactyloscopidae (sand stargazers)
  68b Mouth not vertical. 69  
  69a Teeth brushlike. 70  
  69b Teeth not brushlike. 72  
  70a Body deep or elongate; mouth reaching to past anterior of eye in most species; dorsal and anal fin origins not elongate. Centrarchidae - sunfishes  
  70b Body deep; mouth small, not reaching past anterior of eye. 71  
  71a No large spine at angle in preopercle flap. Chaetodontidae - butterflyfishes  
  71b Large spine at angle in preopercle flap. Pomacanthidae - angelfishs  
  72a Lower membrane of the gill cover broadly joined to isthmus (lower neck area) Eleotridae - sleepers Acanthuridae (surgeonfishes), Labridae (wrasses), Dactylopteridae (flying gurnards)
  72b Lower membrane of the gill cover free or nearly free from the isthmus (though membranes may be united, they are still free from isthmus). 73  
  73a Premaxillaries (front part of upper jaw) extremely protractile. Gerridae - mojarras Opistognathidae (jawfishes)
  73b Premaxillaries only moderately or not protractile. 74  
  74a Body elongate and slender; anal and dorsal fins long, narrow. 75  
  74b Body moderately or very deep. 79  
  75a 2 dorsal fins. 76  
  75b 1 dorsal fin. 77  
  76a Pelvic fin in front of pectoral fin, under head and is filamentous with 2 or more rays. Phycidae - hakes  
  76b Pelvic fin not filamentous. Pomatomidae - bluefishes  
  77a Dorsal fin originating on top of head; no spines in dorsal fin. Coryphaenidae - dolphinfishes  
  77b Dorsal fin originating behind head; dorsal fin with spines. 78  
  78a Body elongate, eel-like; gill openings small, oblique slits before pectoral fins. Microdesmidae - wormfishes  
  78b Gill openings moderate or large Malacanthidae - tilefishes Labrisomidae (librisomid blennies), Chaenopsidae (pike blennies), Bythitidae (viviparous brotulids)
  79a Head short; snout blunt. 80  
  79b Snout pointed. 83  
  80a Dorsal and anal fins lunate (crescent-shaped or fan-shaped; most scales keel in the center. Bramidae - pomfrets  
  80b Dorsal and anal fins not as above; no keels on scales. 81  
  81a Teeth hockey-stick shaped, the bases set horizontally in the mouth. Kyphosidae - sea chubs  
  81b Teeth not as above. 82  
  82a 2 long barbels on chin behind tip of lower jaw. Polymixiidae - beardfishes  
  82b No barbels on chin. Centrolophidae - medusafishes Bregmacerotidae (codlets), Scaridae (parrotfishes)
  83a Body deep; head small; forehead concave; dorsal and anal fins rounded and symmetrical at ends. Lobotidae - tripletails  
  83b Body deep or slender; head not concave. 84  
  84a Very large eye, close to top of head; mouth large; reddish in color (or brown or black). 85  
  84b Not as above. 86  
  85a Mouth very oblique; pelvic fins broadly attached to body; tail not forked. Priacanthidae - bigeyes  
  85b Mouth slightly oblique; pelvic fins only attached to body at base; tail forked. Holocentridae - squirrelfishes Apogonidae (cardinalfishes)
  86a Maxillary, especially posterior end, slips beneath preorbital (bony area beneath eye) completely or partially when mouth is closed; no spines on opercle. 87  
  86b Maxillary not slipping beneath preorbital; opercle usually with 3 flat spines. Serrandiae - groupers/seabasses Acropomatidae (temperate ocean basses), Ariommatidae (driftfishes), Nomeidae (man-of-war fishes), Istiophoridae (billfishes)
  87a Chin with 2 distinct pores; area between eye and mouth scaled. Haemulidae - grunts  
  87b Chin with no pores or many small pores; no scales between eye and mouth. 88  
  88a Teeth on roof of mouth (tiny, like sandpaper); teeth in jaws conical, sometimes with canine teeth; preopercle serrated. Lutjanidae - snappers  
  88b No teeth on roof of mouth; teeth in jaws canine or flat in front, molar-like on sides; preopercle not serrated. Sparidae - porgies