KEY TO FISH FAMILIES IN THE INDOCHINESE
MEKONG
Coverage. This key covers all 93 fish families, hitherto recorded
from fresh- and brackish-water areas of the Mekong Basin, as wellas an additional 3 marine-fish families that are expected to enter thebrackish estuaries in this region (viz., Myliobatidae, Gymnuridae,

and Apogonidae). Note that this key is made based primarily on thefish species of the Indochinese Mekong; namely this key may not
apply to the non-Mekong species of respective families (viz., fishes
from the other geographic regions).

1a. Five pairs of gill openings ……..........................................................................................…. 2
1b. Single pair of gill opening(s) …….......................................................................................... 6

1a

1a

1b

2a. Gill openings located on lateral side of body …................................. Carcharhinidae (p. 34)
2b. Gill openings located on ventral surface of body ….......................................................……. 3
3a. Snout greatly elongate, with a row of distinct thorns on each side, forming saw-likeappearance .................................................................................................... Pristidae (p. 39)
3b. Snout not as in 3a ………....................................................................................................… 4

4a. Eyes located on lateral sides of protruding head …..…..…..................... Myliobatidae (p. 39)
4b. Eyes on dorsal surface of disc ……….......................................................................……….. 55a. Disc much wider than its length; tail relatively short ...........................… Gymnuridae (p. 39)

5b. Disc width subequal to its length; tail long ……..................................… Dasyatididae (p. 35)
6a. Body elongate, encased in bony plates; mouth small, opening at tip of bony tube-like snout….....................................................................................................................................….. 7
6b. Combination of characters not as in 6a. …......................................................................…… 86a6a7a. Pelvic fin absent; no dorsal-fin spines; anal fin absent or, if present, very small and rudimental…................................................................................................……. Syngnathidae (p. 337)

12

7b. Pelvic fin present; usually 5 small isolated spines preceeding soft dorsal fin; anal fin as large
as dorsal fin ……….........................................................................… Indostomidae (p. 336)

8a. Body broad, depressed, and encased in bony plates; snout elongate, flat stick-like; short-based
dorsal and anal fins, each with 5 unbranched rays …...... Pegasidae (not shown in this book)8b. Combination of characters not as in 8a. ….............................................................................. 99a. Body greatly elongate, eel-like or tapering ribbon-like; pelvic fins absent ............................10
9b. Shape of body variable (eel-like in some); pelvic fins usually present (absent in some, but atleast the eel-like species have pelvic fins) ……...............................................................…. 18
10a. Head well compressed and nearly triangular; lower jaw projecting; body well compressed
and ribbon-like, tapering posteriorly ………….................................… Trichiuridae (p. 400)
10b. Combination of characters not as in 10a ……..……........................................................… 1110a11a. A series of many small spines along dorsal midline before soft dorsal fin; 2–3 anal-fin spines...................................................................................................... Mastacembelidae (p. 348)
11b. No spines before soft dorsal fin; no anal-fin spines ............................................................. 1212a. Caudal fin may be separated from dorsal/anal fins; pectoral fin present; 34–48 dorsal-fin rays;
37–48 anal-fin rays; small size (up to 4.5 cm SL) ….......................... Chaudhuriidae (p. 347)
12b. Combination of characters not as in 12a. ............................................................................. 13
13a. Pectoral fins absent ……............................................................................................…….. 14
13b. Pectoral fins present ………….........................................................................................…15

13a

13b

14a. Gill membranes continuous across ventral surface of body ….......... Synbranchidae (p. 344)
14b. A pair of small pore-like gill openings on side of body ............................ Muraenidae (p. 47)

14a

14b

15a. Anus at posterior part of body ……............…................................…... Moringuidae (p. 48)
15b. Anus at or before midlength of body ….....................................................................…. 16

16a. Enlarged teeth at tip of lower jaw; gill openings confined to lower part of body ………...........
....................................................................................................…. Muraenesocidae (p. 51)
16b. No enlarged teeth at tip of lower jaw; gill openings at midside of body …..........……......... 17

16a

13

17a. Lower jaw not projecting beyond upper jaw; no scales on body …....... Ophichthidae (p. 48)

17a

17b

17b. Lower jaw slightly projecting beyond upper jaw; minute embedded scales on body ………...
.................................................................................................................. Anguillidae (p. 46)
18a. Adipose fin present .................……...............................................................................….. 19
18b. Adipose fin absent ……...........................................................................................……… 28
18a

18a

18b

18b

19a. Barbels absent ……...…...........................................................................................……… 20
19b. Barbels present (except for adults of a large pangasiid catfish, Pangasianodon gigas, lacking
barbels) ................................................................................................................................ 21

19a

19a

19b

19b

20a. Body deep and compressed; mouth small ………................................... Characidae (p. 241)20b. Body slender; mouth small to large .....................………..........................…....….............. 21
21a. Mouth small or moderate in size, not reaching posteriorly a vertocal line through posterior
margin of eye; lateral-line scales absent on body ..................................... Salangidae (p. 307)21b. Mouth large, extending posteriorly well beyond a vertical line through posterior margin ofeye; lateral-line scales present on body ............................................... Synodontidae (p. 308)

22a. Body encased in bony plates; mouth ventral; lower lip broad and papillose, forming a semicircular flap …...................................................................................… Loricariidae (p. 304)
22b. Body not encased in bony plates; position of mouth variable; lips not forming a semicircular flap …..........................................................................................................…........ 22

22a

22a

22b

23a. A long-based anal fin, with 24 or more rays …..................................................................... 2323b. Anal-fin base short ………………....................................................................................... 24

23a

23b

24a. Single pair of barbels on ventral surface of lower jaw (except for adults of Pangasianodon
gigas, lacking barbels) ….................................................................….. Pangasiidae (p. 260)

24a

14

24b

24b. Two pairs of barbels on ventral surface of lower jaw …....................…. Schilbidae (p. 274)
25a. Body covered with numerous small tubercles ….............................................……………. 26
25b. Body smooth, without small tubercles ………….............................................................…. 27
25a

25b

26a. Dorsal fin with a strong, pungent spine …...............................………...... Akysidae (p. 296)
26b. Dorsal fin with or without spinous ray, but the spine, if present, not strong and pungent ……..
.............................................................................................................…... Sisoridae (p. 300)
27a. Dorsal fin covered by thick skin; eye minute, sometimes embedded under skin; head and body
reddish brown in many species …...................................….......….. Amblycipitidae (p. 295)
27b. Combination of characters not as in 27a. .......................................…...............................… 28
27a

27b

28a. Nasal barbel present ….……........................................................................Bagridae (p. 282)

28a

28b

28b. Nasal barbel absent ….……........................................................................... Ariidae (p. 276)

29a. Body soft and globular; dorsal and anal fins located at posterior half of body, with no spines;
pelvic fins absent ….................................................……............…. Tetraodontidae (p. 498)
29b. Combination of characters not as in 29a .............................................................................. 30
30a. Both eyes on one side of body; dorsal and anal fins with long bases …...........……….....…. 31
30b. Eyes bilateral; shape of dorsal and anal fins variable …................................................…… 33

30a

30b

31a. Eyes on right side of body ….…………...............................................……. Soleidae (p. 487)
31b. Eyes on left side of body ….............................................................................................….. 32

32a. Pectoral fins present ….................................…….......................…. Paralichthyidae (p. 486)

32b. Pectoral fins absent …...............……......................................……. Cynoglossidae (p. 492)

15

33a. Pelvic fins absent or vestigial at least in adult ……..........................................................…. 34
33b. Pelvic fins present (may be minute) …........................................................................…….. 35

33a

33a

33b

33b

34a. Body slender; small fishes (up to 3.7 cm SL) ….……..............……. Phallostethidae (p. 318)

34b. Body deep and compressed; moderately large-sized fishes, not as in 33a .................................
............................................................................................................. Stromateidae (p. 393)

35a. Body deep and compressed, broad knife-like; a single feather-like dorsal fin; long-based anal
fin, continuous with caudal fin ……..................................................…. Notopteridae (p. 42)
35b. Combination of characters not as in 35a. …................................................…................…. 36
36a. Pelvic fins usually located around, or behind, midpoint of distance between head and originof anal fin (may be slightly anterior to the midpoint in an engraulidid genus, Coilia); no
pelvic-fin spines ..............................................................................................................… 3736b. Combination of characters not as in 36a ……..................................................................… 57

36a

36a

36b

36b

37a. A pair of short fleshy barbels on chin; scales on body large, 23–26 lateral-line scales; dorsal
fin located on posterior part of body, with its base much shorter than anal-fin base …………..
....................................................................................................….… Osteoglossidae (p. 41)
37b. Combination of characters not as in 37a ……................................................……........….. 38
38a. Large gular plate on underside of head …………...........................................................…. 39
38b. Gular plate absent ……........................................................................................................ 40

38a

38b

39a. Body slender; last dorsal-fin ray not elongate; scales small ……........….….. Elopidae (p. 52)

39a

39b

39b. Body deeper; last dorsal-fin ray elongate and filamentous; scales large ….…..........................
..........................................................................................................….. Megalopidae (p. 53)

16

40a. Belly with a series of scutes ………................................................................................…..41
40b. No scutes on belly ….....................................................................................................….. 43

40a

40a

40b

40b

41a. Jaws very long, extending posteriorly well beyond a vertical through hind margin of eye………..........................................................................................….... Engraulididae (p. 54)
41b. Jaws moderate in size, not reaching posteriorly to a vertical through hind margin of eye .... 42

41a

41b

42a. Long-based anal fin, with 30 or more rays …..................................... Pristigasteridae (p. 62)

42b. Short-based anal fin, with less than 30 rays ….........…...........................… Clupeidae (p. 62)
43a. No teeth on jaws ……...............……..........................................................................……. 44
43b. Teeth on jaws (may be minute) …………....................................................................…… 49
44a. Barbels absent or, if present, 1–2 pairs only ….…....…..................................................…. 45
44b. Three or more pairs of short barbels (modified into minute papilla-like processes in many
depressed species of Balitoridae) ..................................................................................... 47

44a

44a

44b

44b

45a. Mouth small; scales minute, 75–91 lateral-line scales; lateral line nearly straight; caudal fin
long and deeply forked .................... Chanidae (only a single species, Chanos chanos, p. 70)
45b. Combination of characters not as in 45a ……................................................…….....……. 46

45a

45a

45a

46a. Mouth ventral, modified into a sucking organ; a small vertically-elongate opening above gillcover …………......................................................................…… Gyrinocheilidae (p. 184)
46a

46b

46b

46b

46b. Position and shape of mouth variable; no additional opening above gill cover ………............
................................................................................................................... Cyprinidae (p. 73)

17

47a. No erectile spine below eye; body elongate and typical loach-like, or depressed and stonefly-like …...............................................................................………….. Balitoridae (p. 202)

46a

46a

46a

46a

47b. A small, posteriorly-directed erectile spine below eye (absent in a few species); bodyelongate and typical loach-like, or relatively deep and compressed …...........................…. 48

47b

47b

47b

47b

48a. Caudal fin truncate or rounded, often weakly emarginate; body slender and elongate …..........
..........................................................……...……. Cobitidae (subfamily Cobitinae) (p. 186)

48b. Caudal fin deeply forked; body deeper ................... Cobitidae (subfamily Botiidae) (p. 194)
49a. Barbels present (may be very short or rudimental in a siluid genus Phalacronotus) .......…. 50
49b. Barbels absent …........................................................................................................……. 53
49a

49a

49b

50a. Two pairs of barbels (may be very short or rudimebtal) …..................…. Siluridae (p. 248)
50b. Four pairs of barbels ..........................................................................................………….. 51
50a

50b

51a. A single strong dorsal-fin spine ………….........................................…… Plotosidae (p. 243)
51b. No dorsal-fin spines ….....................................................................................................… 52
51a

51b

52a. Dorsal-fin base very long ………..........................................................….. Clariidae (p. 244)

52b. Dorsal-fin base short ……..……............................................................… Heteropneustidae[not shown in this book (see p. 243)]18

53a. Upper and/or lower jaws greatly elongate, javelin–line ………..............................………. 54
53b. Both jaws not elongate and javelin-like …………………............….........................…….. 55

53a

53a

53b

54a. Both jaws elongate, javelin-like ………............................................…… Belonidae (p. 334)
54b. Lower jaw elongate, javelin-like and much longer than short triangular upper jaw ….............
.................................................................................................…... Hemiramphidae (p. 329)
55a. Base of anal fin as much as, or shorter than, dorsal-fin base; anal fin of males modified intoa rod-like intromittent organ …......................................................……. Poeciliidae (p. 323)
55b. Base of anal fin much longer than dorsal-fin base; anal fin of males not rod-like …......….. 56

56a. Body semitranslucent when alive; no distinct black spots on dorsal fin; pectoral fin nearly
falcate (rather than rounded) …...........................................….. Adrianichthyidae (p. 326)

56a

56b

56b. Body not semitranslucent; a large black spot on dorsal fin; pectoral fin rounded ……………
…...........................................................….......................................... Aplocheilidae (p. 322)

57a. First dorsal fin comprising a single elongate ray; long-based second dorsal and anal fins; 3 of
5 pelvic-fin rays greatly elongate and filamentous …................… Bregmacerotidae (p. 309)
57b. Combination of characters not as in 57a. ……………...................................…………….. 58
58a. A longitudinal bony ridge (usually with some or more small spines) across middle of cheek……..................................................................................................................................... 58
58b. No distinct bony ridge across middle of cheek ………….................................................... 59

58a

58b

59a. Head moderately deep, not much depressed; a single continuous dorsal fin .............................
.........................................................................................................… Scorpaenidae (p. 352)
59b. Head well depressed; 2 dorsal fins ……...........….......................… Platycephalidae (p. 353)

60a. First dorsal fin with 3 strong spines; head broad, with numerous fleshy flaps; long-based
second dorsal and anal fins; no scales on body .............................… Batrachoididae (p. 310)
60b. Combination of characters not as in 60a ……………..........................…...........…………. 61

19

61a. Two widely–separated dorsal fins; origin of pelvic fin placed well behind a vertical line
through pectoral-fin base ….........................................................................................…… 62
61b. Combination of characters no as in 61a …………….....................……......................…… 64

61a

61b

61b

62a. Lower rays of pectoral fin prolonged and thread-like, separated from main part of the fin;snout rounded and projecting anteriorly beyond jaws ......................… Polynemidae (p. 380)
62b. No thread-like, free pectoral-fin rays; snout not projecting anteriorly beyond jaws …........ 63
63a. Two or 3 anal-fin spines …........................................................................ Mugilidae (p. 312)

63a

63b

63b. Single anal-fin spine …….................................................................…. Atherinidae (p. 318)

64a. Single dorsal fin, with its base much shorter than anal-fin base; first soft pelvic-fin ray greatly
elongate and thread-like in many species ........................................ Osphronemidae (p. 404)
64b. Base of dorsal fin(s) as long as, or longer than, anal-fin base; tip of first soft pelvic-fin ray
slightly elongate in some, but not greatly prolonged and thread-like …............................... 65

65a. Single dorsal fin, confined to posterior half of body …….......................... Toxotidae (p. 385)
65b. Shape of dorsal fin(s) variable, but not as in 65a. ….......................................................…. 66
66a. First 2 anal-fin spines separated from main part of the fin; some lateral-line scales (at least
those on posterior part of body) modified into spiny scutes in many species ……....................
.....................................................................................................….….. Carangidae (p. 390)
66b. No separated anal-fin spines from main part of the fin; no spiny scutes on side od body …. 67

66a

66b

67a. Five or more finlets behind second dorsal and anal fins ……................. Scombridae (p. 398)
67b. No finlets behind second dorsal and anal fins ….................................................................. 68

68a. A pair of long fleshy barbels on chin; dorsal fin swell separated; caudal fin forked; single
anal-fin spine ............................................................................................... Mullidae (p. 371)

68a68b. Combination of characters not as in 68a .............................................................................. 6920

69a. Two or more anal-fin spines .........................................................................................…… 70
69b. Single or no anal-fin spine …….......................................................................................… 92

69a

69b

70a. Two anal-fin spines …..................................................................................................…… 71
70b. Three or more anal-fin spines ……..............................................................................…… 73

70a

70b

71a. Two separated dorsal fins, the anterior (first) one with 6–8 spines and the posterior (second)
one with 1 spine and 8–14 soft rays; relatively short-based anal fin, with 2 spine and 8–18
soft rays ………….......................................….....…… Apogonidae (not shown in this book)71b. Combination of characters not as in 71a. ………….............................................………… 72
72a. Body slender; snout narrowly pointed; mouth small, not reaching to a vertical throughanterior margin of eye; long-based anal fin, with 2 slender spines and 18–23 soft rays ............
...............................................................................................……......... Sillaginidae (p. 371)
72b. Body moderately deep; shape of snout variable, but not narrowly pointed; short-based anal
fin, with 2 spines and 6–8 soft rays .......................................................... Sciaenidae (p. 372)
73a. Three anal-fin spines ….................................................................................................…... 74
73b. Four or more anal-fin spines ……............................................................................……… 90

73a

73b

74a. Pelvic fin rudimentary ..................................................................... Monodactylidae (p. 393)
74b. Pelvic fin moderately developed, not rudimentary ..............................................………… 75

75a. Pectoral fin falcate, longer than head; body extremely deep; mouth greatly protrusible ...........
.............................................................................................................. Drepaneidae (p. 392)
75b. Combination of characters not as in 75a ….................................................................……..7676a. Three flat posteriorly-directed spines at posterior part of operculum ….. Serranidae (p. 362)
76b. Posterior part of operculum with 2 or less spines ....................................................……… 77

76a

76b

21

77a. Two spines at posterior part of operculume, the lower one much larger and stronger thanupper one; body and caudal fin with distinct dusky stripes .................. Terapontidae (p. 384)
77b. Combination of characters not as in 77a …………........................................................….. 78

77a

77a

78a. Anal-fin base long; 13 or more soft anal-fin rays ……................................................……. 79
78b. Anal-fin base relatively short; less than 12 soft anal-fin rays …….................................….. 80

78a

78b

79a. Upper jaw greatly protrusible; caudal fin forked ................................ Leiognathidae (p. 388)

79b. Upper jaw not protrusible; caudal fin truncate .............. Ephippidae (not shown in this book)
80a. Dorsal fin with a deep notch, and the anterior and posterior parts not or barely connected byvery low membrane ............................................................................................................. 81
80b. Dorsal fin with no deep notch, and the anterior and posterior parts broadly connected bymembrane …………....................................................................................................…… 82

80a

80b

81a. Caudal fin forked …......................................................................….. Ambassidae (p. 356)

81b. Caudal fin rounded ………..…...................................................................... Latidae (p. 361)

82a. Mouth greatly protrusible; caudal fin deeply forked …....................…..... Gerreidae (p. 386)
82b. Combination of characters not as in 82a ……..................................................................… 83
83a. Lateral line interrupted at posterior part of body ……................…..............................…… 84
83b. Lateral line continuous ……….................................................................................…...… 86

83a

22

83b

84a. A single pairs or nares ……........................................................................ Cichlidae (p. 368)

84a

84b

84b. Two pairs of nares ….................................................................................. Nandidae (p. 366)

Pristolepis

Nandus85a. Interspace between eye and upper jaw largely scaled …...........…..… Haemulidae (p. 370)
85b. Interspace between eye and upper jaw with no scales ……......................................……… 86

85a

85b

86a. Posterior margin of peropercle smooth ….....................................……...... Sparidae (p. 370)
86b. Posterior margin of preopercle serrated …..............................................................………. 87

86a

86b

87a. Caudal fin truncate or slightly emarginated ….….................................... Lutjanidae (p. 363)

87b. Caudal fin rounded ………….................................................................... Lobotidae (p. 364)
88a. Scales minute, difficult to be counted without magnification; lateral line continuous …...... 89
88b. Scales moderately large; lateral line interrupted at posterior part of body ……............…... 90

88a

88a

88b

88b

89a. Body extremely deep; pelvic fin with 1 spine and 5 soft rays; 4 anal-fin spines …...................
.................................................................................................…..… Scatophagidae (p. 395)

89a

89b

89b. Body moderately deep; pelvic fin with 2 spines and 3 soft rays; 7 anal-fin spines …………...
................................................................................................................... Siganidae (p. 396)

23

90a. Mouth located anteroventral to eye; anal fin with 9–11 spines and 8–12 soft rays …………...
..........................................................................................................… Anabantidae (p. 402)

90b. Mouth located in front of eye; anal fin with 13–15 spines and 17–19 soft rays ………............
......................................................................................................... Helostomatidae (p. 403)

91a. Single long-based dorsal fin; long-based anal fin; separated pelvic fins; lower jaw projecting
beyond upper jaw; lateral line present on body ….................................... Channidae (p. 412)
91b. Combination of characters not as in 91a ……….................................................................. 92
92a. Head greatly depressed; usually 2 separated dorsal fins (1st dorsal fin absent in Tonlesapia);no scales on body; a small pore-like gill opening ….......................... Callionymidae (p. 418)

92a

92a

92a

92a

92b. Combination of characters not as in 92a …….....................................................…………. 93
93a. Single long-based dorsal fin; long-based anal fins; all soft rays of dorsal and anal fins simple(unbranched); no scales on body; pelvic fin with 1 spine and 2–3 soft rays …………..............
.................................................................................................................. Blenniidae (p. 417)

93a

93a

93b. Combination of characters not as in 93a ………..........................……..........................….. 94
94a. Pelvic fins usually united medially, forming a disc (if not, the length of base of second dorsal
fin longer than distance from posterior end of second dorsal fin to base of caudal fin) ……….
..................................................................................................................... Gobiidae (p. 430)

94a

94b

94b. Pelvic fins separated ……………………...................................................................……. 95
95a. Multiple rows of minute cuboid cteni present around base of peripheral normal (spine-like)cteni ……….................................................................................…. Odontobutidae (p. 420)

95a

95a

95b. Scale ctani, if present, uniserial and spine-like, with no additional cuboid cteni around base(all scales cycloid in some species) …................................................... Eleotrididae (p. 421)

95b

24

95b

25