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.

	Couplet	Characters	Goto	Pics	Other 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