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