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