fishes

Angulo, Arturo, Gil-León, Jorge San, Oviedo-Soto, Alejandro, Abarca- Odio, Juan I. & Umaña-Villalobos, Gerardo, 2020, The fishes from the Coto River basin, Pacific coast, Costa Rica, Zootaxa 4751 (1), pp. 1-28 : 18-24

Key to species of fishes from the Coto River basin, Pacific coast, Costa Rica

The following key is based on our research and data available in the literature ( Bussing 1987, 1998, Angulo et al. 2015 and Robertson & Allen 2015).

1 Body asymmetrical, strongly compressed laterally; both eyes on the same side of head.............................. 2

- Body symmetrical, not strongly compressed laterally; one eye on each side of head................................. 3

2 Pigment and eyes on the left side of fish ( PARALICHTHYIDAE ) …....................... Citharichthys gilberti ( Fig. 8C ; Other diagnostic features include: teeth equally developed on both sides of the jaws, in a single series of immovable teeth on each jaw, no canines but front teeth a little enlarged; gill rakers slender, moderately long, lower rakers 12–15; length of the pectoral fin of the eyed side 43–59% of head length)

- Pigment and eyes on right side of fish ( ACHIRIDAE ) ….. Trinectes fonsecensis ( Fig. 8B ; Other diagnostic features include: interbranchial foramen absent; dorsal fin rays 58–60; scales on eyed side without black hair like filaments)

3 Body covered by bony plates or rings..................................................................... 4

- Body not covered by bony plates or rings, naked or with normal scales.......................................... 7

4 Body robust to elongated, covered by a kind of armor composed by a series of bone segments in the form of plates; mouth ventral, intermediate in size, with teeth, prominent lips with papillae (small projections) and chins, snout non-tubular; eyes in dorsolateral position; pelvic fins present ( LORICARIIDAE )................................................... 5

- Body slim and extremely elongated, covered by a kind of armor composed by a series of bone segments in the form of rings; mouth small, without teeth or prominent lips, located at the end of a long and tubular snout; eyes in lateral position; pelvic fins absent ( SYNGNATHIDAE ) ….......................................................................... 6

5 Ventral portion of the body (abdomen) naked, not covered by no or few bone plates (the species has abdominal plates in other portions of its range); adipose fin present; caudal peduncle not very elongated (postdorsal portion of body shorter or about equal than the predorsal portion) nor dorsally compressed …...... Hypostomus aspidolepi s ( Fig. 8 H–I; Other diagnostic features include: general coloration greenish-brown to reddish-brown with black circular blotches on fins and the ventral portion of the body, which tend to be more pronounced at the anterior portion of the body; adipose dorsal fin with strong spines)

- Ventral portion of the body (abdomen) covered by bone plates; adipose fin absent; caudal peduncle elongated (postdorsal portion of body larger than the predorsal portion) and dorsally compressed …..................... Rineloricaria uracantha ( Fig. 8J ; Other diagnostic features include: general coloration yellowish-brown to gray, darker dorsally, with four or five gray or black bars crossing the dorsum, abdomen straw-colored, fins yellowish-brown to grayish with black spots)

6 Dorsal fin rays 37–44; snout short 35–37% of head length; head with a dark lateral stripe …............... Pseudophallus elcapitanensis ( Fig. 8M ; Other diagnostic features include: general coloration dark brown, usually darker dorsally, with lighter specks along the body)

- Dorsal fin rays 30–35; snout long 38–43% of head length; head without marks ….... Pseudophallus starksii ( Fig. 8M ; Other diagnostic features include: general coloration dark or light brown dorsally with the belly always pale, light yellow to straw)

7 Pectoral and pelvic fins absents; dorsal, anal and caudal fins vestigial ( SYNBRANCHIDAE ) … Synbranchus marmoratus ( Fig. 8L ; Other diagnostic features include: body elongated, anguilliform; scales absent; general coloration grayish-brown or yellowish-brown, darker above and paler with dark speckles ventrally)

- Pectoral, pelvic, dorsal, anal and caudal fins presents and well developed …...................................... 8

8 Pelvic fins united into an adhesive disc..................................................................… 9

- Pelvic fins separated, not in the form of an adhesive disc...................................................… 11

9 Upper jaw teeth minute, compressed; gill rakers absent; adhesive disc circular, its width greater than its median length; males with the first dorsal fin spines elongated (filamentous).................. Sicydium salvini ( Fig. 6 M–O; Other diagnostic features include: general coloration dark brown to grayish or yellowish brown, darker dorsally and paler ventrally, usually with 6–7 dark bars on the sides and/or a longitudinal dark band; dorsal margin of the dorsal, anal and caudal fins usually red)

- Upper jaw teeth conspicuous, conical to caniniform; gill rakers present; adhesive disc oval, its width less than its median length; first dorsal fin spines not elongated................................................................... … 10

10 Snout pointed in lateral view; scales in lateral series 67–73; second dorsal fin short, with 9–12 rays; anal fin short, with 9–11 rays; caudal fin short, about equal to head length, and rounded … Awaous transandeanus ( Fig. 6 J–K; Other diagnostic features include: general coloration light brown dorsally, with the sides light yellow to tan; ventral surface white or pale yellow; sides of head with 3 black slanted bars; body with about 7 irregular black bars on the upper side and 7–8 black blotches on the flanks; back with a series of black irregular small spots, in front of and along the first dorsal fin; dorsal fin yellowish)

- Snout rounded in lateral view; scales in lateral series 55–65; second dorsal fin long, with 12–15 rays; anal fin short, with 13–15 rays; caudal fin relatively long, larger than head length, and pointed......................................................................... Ctenogobius sagittula ( Fig. 6L ; Other diagnostic features include: head and body light tan, with 4 dark brown blotches along the middle of the sides plus a dark brown spot at the middle of the caudal fin base; a brown stripe on the cheek and a brown blotch just behind the center of the gill cover; a dark blotch on the side of the nape, above the pectoral fin base; second dorsal and caudal fin with brown spots)

11 Body naked; barbels present........................................................................... 12

- Body covered by scales; barbels absent.................................................................. 15

12 Opercular odontodes present; pectoral and dorsal fin spines absent; dorsal adipose fin absent; caudal fin rounded to truncate ( TRICHOMYCTERIDAE )............................... Trichomycterus striatus ( Fig. 8K ; Other diagnostic features include: general coloration brown, light brown, yellowish or light orange, darker on dorsal surface, and paler ventrally, usually with a continuous black lateral band (of variable thickness), extending from opercle to caudal-fin base; paired, dorsal and anal fins light brown, yellowish (usually darker at base) or translucent; caudal fin brown or yellowish)

- Opercular odontodes absent; pectoral and dorsal fin spines present; dorsal adipose fin present; caudal fin forked (HEPTAPTER- IDAE)............................................................................................. 13

13 Occipital process continuous with the osseous plate of the dorsal spine (see Fig. 22a in Bussing 1998, page 143); dorsal fin spine strong and pungent, like the pectoral spine................................ Pimelodella chagresi ( Fig. 8D ; Other diagnostic features include: general coloration light brown to light gray with a lateral band of intensive black color that extends from the tip of the snout to the edge of the caudal fin and another dark band, a bit thinner, in the dorsal margin, from the nape to the caudal peduncle; maxillary barbels extending to the end of the dorsal fin)

- Occipital process no continuous with the osseous plate of the dorsal spine, i.e., not reaching the dorsal plate (see Fig. 22a in Bussing 1998, page 143); dorsal-fin spine weak and usually flexible............................................ 14

14 Maxillary barbels long, usually extending beyond the origin of the dorsal fin; serrations present on both margins of the pectoral spines; space between the dorsal and adipose fins shorter than the length of the base of the dorsal fin................... Rhamdia guatemalensis ( Fig. 8 E–F; Other diagnostic features include: general coloration dark gray to grayish-brown, darker dorsally and paler ventrally, some specimens shows a lateral black band of variable thickness)

- Maxillary barbels short, not extending beyond the pectoral fins; serrations present only on the inner (posterior) margin of the pectoral spines, sometimes without serrations; space between the dorsal and adipose fins usually larger than the length of the base of the dorsal fin........... Rhamdia laticauda ( Fig. 8G ; Other diagnostic features include: general coloration gray to grayish-brown or yellowish-brown, darker dorsally and paler ventrally)

15 Dorsal adipose fin present............................................................................. 16

- Dorsal adipose fin absent.............................................................................. 22

16 Anal fin rays 8–10................................................................................... 17

- Anal fin rays more than 20............................................................................ 18

17 Body rhomboidal, higher in the middle portion of the body (approximately at the origin of the dorsal fin), slightly compressed laterally; teeth absent; eye diameter greater than the length of the mouth; longitudinal series with 36–37 scales (CURIMATI- DAE).. Cyphocharax magdalenae ( Fig. 2 L–M; Other diagnostic features include: general coloration silver to silvery-golden, without marks on body; fins transparent, yellowish or brownish)

- Body elongate, fusiform, height relatively uniform along the body, robust, not compressed laterally; eye small, eye diameter less than the length of the mouth; teeth present; longitudinal series with 26–27 scales ( LEBIASINIDAE )................ Lebiasina boruca ( Fig. 3 A–B; Other diagnostic features include: general coloration silver to gray above and on the flanks and white below, with three longitudinal red stripes on each side formed by a red blotch on each scale of the three lateral rows; fins transparent, yellowish, reddish or brownish)

18 Upper jaw projected anteriorly (i.e., its anterior margin clearly surpasses the anterior margin of the lower jaw in the vertical plane); upper jaw with three or four rows of teeth (in ventral view); adults easily exceeding 15 cm in total length (BRYCONI- DAE). Brycon behreae ( Fig. 2 C–E; Other diagnostic features include: general coloration greenish-silvery to pinkish-silvery, greenish-gray dorsally, whitish-gray dorsally; fins transparent to reddish or yellowish-gray)

- Upper jaw not very projected anteriorly (i.e., its anterior margin about at the same level as the anterior margin of the lower jaw in the vertical plane); upper jaw with one or two rows of teeth (in ventral view), in Roeboides (see below) it is also possible to observe two pairs of external teeth in the premaxilla; adults not exceed 15 cm in total length ( CHARACIDAE )......... 19

19 Body strongly compressed; nape concave; two pairs of external teeth on premaxillary; anal fin very long, with 42–45 rays.. Roeboides bussingi ( Fig. 2 I–K; Other diagnostic features include: general coloration yellowish-silvery; fins transparent to yellowish-orange or red)

- Body not strongly compressed; nape convex or straight; no external teeth on premaxillary; anal fin short, with 20–29 rays... .................................................................................................. 20

20 Premaxillary teeth in two rows; humeral spot present, always shaped like the letter P; caudal fin usually without yellow spots; maximum body size about 130 mm SL................................................... Astyanax orstedii ( Fig. 2F ; Other diagnostic features include: general coloration grayish to withish-silvery, darker dorsally, usually greenish-brown or gray, and paler ventrally; fins transparent to yellowish-orange or red)

- Premaxillary teeth in a single row; humeral spot absent or, if present, not shaped like a letter P; caudal fin with two yellow spots, above and below the dark caudal fin blotch; maximum body size about 50 mm SL................................ 21

21 Maxillary long, its length 52.6–58.5% of eye diameter; upper margin of the eye usually without pigment or brownish; anal fin rays 20–23... Odontostilbe dialeptura ( Fig. 2G ; Other diagnostic features include: general coloration yellowish-silvery; fins transparent to yellowish-orange)

- Maxillary short, its length 28.6–43.5% of eye diameter; upper margin of the eye usually reddish; anal fin rays 23–27....... Pseudocheirodon terrabae ( Fig. 2H ; Other diagnostic features include: general coloration whitish to yellowish-silvery; fins transparent to yellowish-orange or red)

22 One dorsal fin...................................................................................... 23

- Two dorsal fins..................................................................................... 48

23 Fins without spines; caudal fin rounded.................................................................. 24

- One or more fins with prominent spines; caudal fin slightly rounded or truncated to forked......................... 36

24 Maxillary bone long, extending beyond the posterior margin of the eye in the vertical plane; anal fin origin located posterior to the posterior insertion of the dorsal fin in the vertical plane, closer to the caudal fin origin than to the dorsal fin origin (ERY- THRINIDAE)........... Hoplias microlepis ( Fig. 2 N–O; Other diagnostic features include: mouth large, with a few long, sharp teeth; pelvic fins placed well back on the abdomen; general coloration brown to yellowish-brown, darker dorsally, paler ventrally, with darker blotches on the back and light brown to white blotches on the lower part of the flanks and the abdomen; all fins dark brown with some clear areas alternating with brown blotches)

- Maxillary bone long, usually not reaching the anterior margin of the eye in the vertical plane; anal fin origin usually located anterior to the dorsal fin origin, not very close of the caudal fin origin.......................................... 25

25 Eyes with free borders; dorsal fin origin at or very close to the middle of the body; males with anal fin modified into a copulatory organ called gonopodium; third anal fin ray not branched ( POECILIIDAE ).................................. 26

- Eyes with or without free borders; dorsal fin origin at the posterior portion of the body, close to the caudal fin origin; males with normal anal fin, i.e. not modified into a gonopodium; third anal fin ray (counting rudiments) branched................ 33

26 Anal fin with a black blotch........................................................................... 27

- Anal fin clear or dusky, without a black blotch............................................................. 28

27 Predorsal distance 45.45–52.63% of standard length; dorsal fin rays 10 o 11....................................... Brachyrhaphis roseni ( Fig. 5 C–D; Other diagnostic features include: dorsal fin base short, usually shorter or of the same length than head length; general coloration yellowish-brown to reddish-brown, darker dorsally and paler ventrally, with 12 dark bars on the sides; anal fin usually yellowish; margin of the caudal fin usually orange with a darkened submarginal band in males)

- Predorsal distance 50.00–62.50% of SL; dorsal fin rays 12–16............................. Brachyrhaphis terrabensis ( Fig. 5F ; Other diagnostic features include: dorsal fin base long, longer than head length; general coloration yellowish-brown to reddish-brown, darker dorsally and paler ventrally, with diffuse dark vertical bars, more conspicuous in adults, and a tenuous dark band along the body; anal fin usually yellowish-orange to reddish; margin of the caudal fin usually usually bluish-white)

28 Pelvic fins of mature males modified, with the tip of first ray with a soft swelling and the second ray thickened; gonopodium short, rarely reaching the posterior insertion of the dorsal fin in the vertical plane; dorsal fin origin of females usually above the origin of the anal fin in the vertical plane; dorsal fin usually with black spotting or a blotch proximally; cross-hatch pattern faint; caudal fin profusely spotted its base, often on entire fin; rows of yellow or black spots along sides...... Poecilia gillii ( Fig. 5 G–H; Other diagnostic features include: general coloration yellowish-silver to greenish-silver, with blue highlights, the dorsum usually greenish-brown and the ventral portion withish-silver)

- Pelvic fins not modified in males; gonopodium relatively long, reaching or extending beyond the posterior insertion of the dorsal fin; dorsal fin origin of females slightly behind the anal fin origin in the vertical plane; dorsal fin usually without black spotting or a blotch proximally (present in Priapichthys panamensis ; see below); cross-hatch pattern on body usually evident .................................................................................................. 29

29 Dorsal and caudal fins with small brown blotches at the proximal half of the fin......................... Priapichthys panamensis ( Fig. 5N ; Other diagnostic features include: predorsal profile slightly convex; dorsal fin inserted behind the anal fin base; general coloration yellowish-brown, with 3–7 thin dark bands on the sides; fins usually transparent or yellowish)

- Dorsal and caudal fins without small brown blotches........................................................ 30

30 Two or three oval black spots present on flanks..... Poeciliopsis paucimaculata ( Fig. 5J ; Other diagnostic features include: predorsal profile convex; gill rakers 19–20; dorsal scales with dark brown posterior borders)

- No black oval spots on flanks.......................................................................... 31

31 Sides of body without marks.. Poeciliopsis retropinna ( Fig. 5L ; Other diagnostic features include: predorsal profile slightly convex; gill rakers 27–34; general coloration grayish-brown; fins usually transparent)

- Sides of body with 6–9 narrow bars..................................................................... 32

32 Total gill rakers 29–32; pectoral fin longer, usually reaching middle of pelvic fin and to within an eye diameter of dorsal-fin origin. Poeciliopsis elongata ( Fig. 5I ; Other diagnostic features include: predorsal profile slightly convex to straight; general coloration grayish-brown to yellowish-brown; fins usually transparent to yellowish-gray)

- Total gill rakers 15–22; pectoral fin short, usually not extending to middle of pelvic fin, nor within an eye diameter of dorsal-fin origin … Poeciliopsis turrubarensis ( Fig. 5M ; Other diagnostic features include: predorsal profile straight; dorsal fin inserted forward of the end of the anal fin base; general coloration yellowish-brown to yellowish-gray; fins usually transparent to yellowish-gray)

33 Snout prominent, elongated, its length corresponds to the double or almost the double of the diameter of the eye; eyes with free borders, the upper portion silvery; predorsal profile straight ( ANABLEPIDAE ) … Oxyzygonectes dovii ( Fig. 5 A–B; Other diagnostic features include: general coloration gray, brown or yellowish-brown, darker dorsally becoming white on the abdomen; fins usually yellowish or grayish; mature males with dark brown bars on the posterior half of the flanks)

- Snout relatively short, its length equal to or similar to the eye diameter; eyes without free borders, the upper portion usually brown, never silvery; predorsal profile curved ( RIVULIDAE )................................................ 34

34 E-type frontal scalation ( Fig. 9B ); mature males with the outer margin of the caudal fin yellow-orange.................. Cynodonichthys hildebrandi ( Fig. 5P ; Other diagnostic features include: both sexes with about the same coloration pattern, i.e., dark brown to grayish-brown or golden brown, lacking of bright colors, and with small light brown spots on the sides; females with a dark (ocellated) spot on the dorsal portion of the caudal fin base)

- D-type frontal scalation ( Fig. 9A ); mature males with the outer margin of the caudal fin transparent, brown or light blue, not yellow-orange...................................................................................... 35

35 Total gill rakers 7–10; dorsal fin rays 11 or 12; anal fin rays 13–15.......................... Cynodonichthys glaucus ( Fig. 5O ; Other diagnostic features include: females yellowish to reddish-brown with small light brown spots on the sides and a dark (ocellated or non-ocellated) spot on the dorsal portion of the caudal fin base; mature males reddish-brown, darker dorsally and paler ventrally, with bluish iridescent hues and red spots on the posterior half of the body, anal fin yellowish, caudal fin pinkish-brown)

- Total gill rakers 6–8; dorsal fin rays 9–11; anal fin rays 11–14.................. Cynodonichthys uroflammeus ( Fig. 5Q ; Other diagnostic features include: females yellowish to grayish-brown with small light brown to yellowish-brown spots on the sides and a dark (non-ocellated) spot on the dorsal portion of the caudal fin base; mature males with the head, the posterior half of the body and the base of the caudal fin reddish-orange, anteromedial portion of the body reddish-blue; pectoral, pelvic and anal fins greenish-yellow, dorsal fin bluish-green, caudal fin with the distal margin yellowish and bluish with a dark band)

36 A single nasal opening on each side of the head; lateral line discontinuous; caudal fin slightly rounded to truncated (CICHLI- DAE)............................................................................................. 37

- Two nasal openings on each side of the head; lateral line continuous; caudal fin truncated to forked................... 43

37 Anal fin with 3 spines................................................................................ 38

- Anal fin with 4–8 spines … 39

38 Two or three emerald green stripes present below the eye; emerald green spots present on head, sides and fins; caudal fin without black bars................................ Andinoacara coeruleopunctatus ( Fig. 3 E–H; Other diagnostic features include: general coloration greenish to yellowish-silvery, darker dorsally, paler ventrally, usually with a black blotch under the spinous portion of the dorsal fin and 6–7 dark bars on the sides; maximum body size 115 mm SL)

- No emerald green stripes present below the eye; black to dark brown spots usually present on head, sides and fins; caudal fin with numerous black bars...................................................................................... Oreochromis niloticus ( Fig. 4 C–D; Other diagnostic features include: general coloration pinkish or greenish-gray to grayish-brown; fins usually transparent or pinkish-gray with dark spots or bars)

39 Predorsal profile usually convex; mouth subinferior; teeth of outer row spatulate and bicuspid; anal fin spines 4–5......... Talamancaheros sieboldii ( Fig. 4 G–K; Other diagnostic features include: general coloration yellowish to greenish-brown, darker dorsally and paler (usually withish) below, with the flanks usually golden to reddish, a black margined mask, formed by two black lines that crosses the snout joining the two golden colored eyes, and 6 dark broad bars on the sides; fins usually yellowish-brown to reddish brown or slightly transparent with small dark spots)

- Predorsal profile nearly straight to convex; mouth terminal or subterminal; teeth of outer row sharp, conical, cylindrical and unicuspid; anal fin spines 5–8.......................................................................... 40

40 Mouth large, usually more than 30% of head length, with the posterior edge usually reaching (or very close of) the anterior edge of the eye in the vertical plane; lower jaw projected anteriorly (i.e., its anterior margin clearly surpasses the anterior margin of the lower jaw in the vertical plane); large caniniform teeth present on both jaws; anal fin spines 6–8.................... Parachromis managuensis ( Fig. 4 E–F; Other diagnostic features include: iris usually red; lower angle of the preopercle with a fleshy lobe; general coloration yellowish, purplish or greenish-brown, with the dorsal portion darker, usually moss-green, the sides golden with purple iridescence and the ventral portion paler, usually yellowish-white, with black spots on the sides and fins and a more or less continuous black band between the eye and the caudal fin)

- Mouth short, usually less than 30% of head length, with the posterior edge not reaching the anterior edge of the eye in the vertical plane; mouth terminal, both jaws of equal length; large caniniform teeth usually absent; anal fin spines 5–6......... 41

41 Lower lip continuous, without a frenum (see Bussing 1998); iris reddish; no emerald green or light blue spots present on head, sides and/or fins......... Amphilophus lyonsi ( Fig. 3 C–D; Other diagnostic features include: general coloration greenish to yellowish-brown, with 7–8 black squares or diffuse bands on the sides, between the opercle and the caudal fin)

- Lower lip not continuous, with a frenum (see Bussing 1998); iris usually yellowish, not reddish; emerald green or light blue spots present on head, sides and/or fins................................................................... 42

42 Dorsal fin with 17–18 spines; anal fin with 4 or 5 spines; emerald green or light blue spots present on head.... Cribroheros altifrons ( Fig. 3 I–K; Other diagnostic features include: general coloration greenish to yellowish-brown, with 5 broad black bars on the sides and a black, sometimes diffuse, lateral band between the eye and the caudal fin; fins usually transparent or bluish to greenish-yellow, with emerald green, light blue or transparent spots; dorsal margin of the dorsal fin reddish with a bluish band)

- Dorsal fin with 15–16 spines; anal fin with 5–7 spines; no emerald green or light blue spots present on head… Cribroheros diquis ( Fig. 3L , 4 A–B; Other diagnostic features include: general coloration yellowish to grayish-brown, with 6 broad black bars on the sides and a black, sometimes diffuse, lateral band between the opercle and the caudal fin;)

43 Premaxillaries extremely protractile (i.e., mouth highly extensible, pointing downward when protruded); tail forked; body color silvery ( GERREIDAE )............................................................................... 44

- Premaxillaries slightly protractile or not protractile; tail emarginate or truncate; body color variable.................. 46

44 Body an elongate oval (depth about 40% of standard length); upper profile of head almost straight; lower profile of head distinctively concave; lower border of preopercle smooth; spiny dorsal fin with a gray base, white center and a wide black tip; pelvic and anal fins usually grayish; lateral line scales 44–48; anal fin with 7 rays............. Eucinostomus currani Fig. 7 G–H)

- Body rhomboidal (depth about 50% of standard length); upper profile of head convex; lower profile of the head concave; lower border of preopercle serrated; dorsal fin uniformly transparent or grayish; pelvic and anal fins yellowish; lateral line scales 37–40; anal fin with 8 rays............................................................................ 45

45 Lips not thick and fleshy; preorbital bone smooth; body without dark longitudinal stripes.... Diapterus peruvianus ( Fig. 7F ; Other diagnostic features include: pectoral fins relatively long, reaching slightly beyond anal fin origin)

- Lips thick and fleshy; preorbital bone serrated; body with dark longitudinal stripes.... Eugerres brevimanus ( Fig. 7I ; Other diagnostic features include: pectoral fin short, not reaching past the pelvic fins)

46 Snout, below eye and lower jaw with scales; vomer without teeth; jaw teeth usually of the same size; dorsal fin with 12–13 spines and 12 rays, deeply notched between the spiny and soft parts ( HAEMULIDAE )..... Rhonciscus bayanus ( Fig. 7 J–K; Other diagnostic features include: second anal spine very long and stout, its length about two times or more, the eye diameter; pectoral fins relatively short, not reaching the tips of the depressed pelvic fins; pelvic fins short, not reaching the anus; general coloration yellowish to greenish-silvery, with an orange tint on sides; fins orange; juvenile with wavy stripes)

- Snout, below eye and lower jaw without scales; vomer with teeth, often small; some jaw teeth usually enlarged to form canines; dorsal fin with 10 spines and 12–14 rays, moderately notched between the spiny and soft parts ( LUTJANIDAE )........ 47

47 Body color rosy red anteriorly becoming bright yellow to orange, with a blue horizontal streak below eye and without a distinctive black spot on the back; dorsal fin rays 14.................................................................... Lutjanus argentiventris ( Fig. 7L ; Other diagnostic features include: tooth patch at the central roof of the mouth anchor shaped, front curved or pointed; scale rows on upper the back parallel to lateral line)

- Body color pale crimson or pinkish to yellowish with silvery sheen, without a blue horizontal streak below eye but with a distinctive black spot on the back below the middle portion of the dorsal fin; dorsal fin rays 12–13.......... Lutjanus guttatus ( Fig. 7M ; Other diagnostic features include: tooth patch at the central roof of the mouth in a V, with a moderately long pointed rear extension; scale rows on the upper back rising obliquely above lateral line)

48 Lateral line absent; scales usually smooth, cycloid; pelvic fins located completely in front of the origin of the dorsal fin in the vertical plane....................................................................................... 49

- Lateral line present; scales rough, ctenoid or needle shaped; pelvic fins located below or behind the origin of the dorsal fin in the vertical plane (except in Oligoplites altus , CARANGIDAE )............................................... 57

49 Body brownish, usually with red, black, green, golden or purple blotches; distance between both dorsal fins less than the length of the base of the first dorsal fin; pelvic fin in an anterior position, its origin located below or very close to the origin of the pectoral fins in the vertical plane; caudal fin rounded or convex ( ELEOTRIDAE )................................. 50

- Body silver or yellowish, usually without spots; distance between both dorsal fins greater than the length of the base of the first dorsal fin; pelvic fin in a posterior position, its origin located below or after half of the pectoral fin (extended over the body) in the vertical plane; caudal fin concave or slightly forked...................................................... 55

50 Mouth relatively short, usually less than 30% of head length; eyes on the side of the head (except in Leptophilypnus panamensis in which they are in a dorsolateral position); scales in the longitudinal series 25–36............................... 51

- Mouth large, usually more than 30% of head length; eyes on the top of the head; scales in the longitudinal series 51–68 … 53

51 Body robust, high, with the head length usually less than the maximum body height; head with scales; first dorsal fin with 7 spines; a prominent blue spot behind the posterodorsal edge of the opercle, i.e., in the humeral region................... Dormitator latifrons ( Fig. 6A ; Other diagnostic features include: general coloration dark brown to purplish, with 7–8 narrow (one scale wide) forward pointing oblique bars on the upper sides, a dark bar under the eye, and several dark brown stripes on the side of the head behind eye; pectoral fin yellowish-brown with a dark bar on the base; second dorsal and anal fins with rows of brown, yellow or red spots.)

- Body elongated, cylindrical, with the head length usually greater than the maximum body height; head without scales; first dorsal fin with six spines; without a blue ear spot behind the posterodorsal edge of the opercle....................... 52

52 Head compressed dorsoventrally; eyes in dorsolateral position, interorbital space less than 50% of the eye diameter; without a conspicuous black band along the body… Leptophilypnus panamensis ( Fig. 6I ; Other diagnostic features include: general coloration brown, paler ventrally, with three to six dark vertical streaks beneath the pectoral fins and dark spots on the trunk, coalescing in some to form four or five indistinct midlateral blotches; fins transparent to grayish with several vertical bars formed by several brown to red spots)

- Head laterally compressed; eyes on the sides of the head, interorbital space about 50% of eye diameter; a black band present along the body, bordered above and below by iridescent greenish to yellowish stripes.... Hemieleotris latifasciata ( Fig. 6H ; Other diagnostic features include: general coloration greenish-brown, with the sides yellowish and the belly pearl white; dorsal fin with some dark spots near the base; caudal fin transparent except for the lateral band extending onto the middle rays; paired and anal fins transparent)

53 Gill opening large, extending ventrally to almost below the oral commissure; vomer with teeth; preopercle without a ventral spine................................................................................................. Gobiomorus maculatus ( Fig. 6 E–G; Other diagnostic features include: general coloration greenish to yellowish-brown, with the sides yellowish and the belly pearl white and black, brown or red spots on the sides and fins)

- Gill opening narrow, extending below the opercle, far behind the eye; vomer without teeth; preopercle with a ventral spine usually covered by skin.................................................................................. 54

54 Scales small, lateral scales 60–68, transverse scales (between the origin of the second dorsal fin and the base of the anal fin) 21–24; pectoral fin rays usually more than 17, 18–19.... Eleotris picta ( Fig. 6 B–C; Other diagnostic features include: head, body and fins dark blackish to greenish brown, with a paler belly; some specimens with the inverse pattern, i.e., dorsal portion of the body light brown and ventral portion darker)

- Scales large, lateral scales 54–60, transverse scales (between the origin of the second dorsal fin and the base of the anal fin) 15–18; pectoral fin rays 16 or 17, usually 17... Eleotris tecta ( Fig. 6D ; Other diagnostic features include: general coloration dark to pale brown, uniform or slightly paler ventrally; fins with transparent to grayish with spots)

55 Body elongated and laterally compressed, with adult specimens not exceeding 14 cm in total length; body with a thick, silvery lateral strip, usually delineated, in its posterior portion, by a thinner black strip; origin of the first dorsal fin located behind the midline of the body in the vertical plane, usually behind the origin of the anal fin; caudal fin deeply forked (ATHERINOPSI- DAE)........................................ Atherinella argentea ( Fig. 2 A–B; Other diagnostic features include: lower jaw angled sharply upwards; top jaw extendible; first dorsal fin small with 3–5 spines, the middle spine longest, and the origin a little behind the origin of the anal fin; general coloration silvery)

- Body slightly elongated, robust, not compressed laterally, with adult specimens easily exceeding 15 cm in total length; silver side stripe absent; origin of the first dorsal fin located in front of the midline of the body in the vertical plane, always ahead of the origin of the anal fin; caudal fin slightly forked, concave or truncate ( MUGILIDAE )........................... 56

56 Interorbital space curved; eyes without transparent fatty eyelid; pectoral fin insertion usually below the upper edge of the eye in the horizontal plane; anal fin with 2 spines........ Dajaus monticola ( Fig. 6P ; Other diagnostic features include: general coloration olive above, white below, with the dorsal scales with dark edges forming crisscross lines; fins yellowish)

- Interorbital space flattened; eyes mostly covered by transparent fatty eyelid; pectoral fin insertion usually above the upper edge of the eye in the horizontal plane; anal fin with 3 spines....................................... Mugil setosus ( Fig. 6Q ; Other diagnostic features include: general coloration olive to blue on back, silver on sides, and white below, with about 6 dark stripes along flank, a large blackish blotch at the upper base of the pectoral fin, and a medium to large gold blotch on the operculum; pelvic fins yellowish, second dorsal fin uniformly dark, anal fin dark, other fins whitish)

57 Upper jaw projected anteriorly (i.e., its anterior margin clearly surpasses the anterior margin of the lower jaw in the vertical plane); mouth large, with its posterior limit clearly exceeding the posterior limit of the eye on the vertical axis; pectoral fin divided into two portions, the ventral portion, located below the gills, with 5–7 free filaments; distance between both dorsal fins equal to or greater than the length of the base of the first dorsal fin ( POLYNEMIDAE )..... Polydactylus approximans ( Fig. 8A ; Other diagnostic features include: lateral line extending onto caudal fin, with 56–63 scales; general coloration yellowish or whitish to bluish-silver, darker dorsally; the main part of the pectoral fins black.)

- Upper jaw not projected projected (i.e., its anterior margin about at the same level as the anterior margin of the lower jaw in the vertical plane); mouth medium to large, with its posterior end usually not exceeding the posterior limit of the eye on the vertical axis (except in Oligoplites altus , CARANGIDAE ); pectoral fin not divided into two parts; distance between both dorsal fins less than the length of the base of the first dorsal fin........................................................ 58

58 Lateral line not extending to the end of the caudal fin; caudal peduncle slender; second dorsal fin large, with 20–21 rays; anal fin large, with 19–20 rays ( CARANGIDAE )..... Oligoplites altus ( Fig. 7A ; Other diagnostic features include: no scutes on lateral line; general coloration silvery, greenish on upper back, yellowish on the belly; pectoral and tail fins yellow)

- Lateral line extending to the end of the caudal fin; caudal fin peduncle thick; second dorsal fin short, with 9–11 rays; anal fin short, with 6–7 rays ( CENTROPOMIDAE )............................................................... 59

59 Gill rakers 26–31; lateral line grayish, with 47–55 scales; pelvic and anal fins yellowish ... Centropomus robalito ( Fig. 7E ; Other diagnostic features include: eye short, usually shorter than 15% of head length; second anal spine very stout, much longer than the third, reaching to or beyond the level of the caudal fin base when depressed and clearly exceeding the longest anal fin soft ray length)

- Gill rakers 19–26; lateral line blackish, with 61–72 scales; pelvic and anal fins transparent, whitish, grayish or blackish... 60

60 Gill rakers 22–26; distal portion of pelvic fins black; second and third anal spines long, larger than longest anal fin ray; anal fin rays 7; scales around caudal fin base 18–21.......................................... Centropomus medius ( Fig. 7B ; Other diagnostic features include: eye large, usually greater than 15% of head length; second and third anal spines long, about equal in length, nearly reaching the caudal fin, second spine thicker than third)

- Gill rakers 19–23; distal portion of pelvic fins of the same color of the rest of the fin; second and third anal spines short, shorther than longest anal fin ray; anal fin rays 6; scales around caudal fin base 25–30.......................... Centropomus nigrescens ( Fig. 7 C–D; Other diagnostic features include: eye short, usually shorter than 15% of head length; second and third anal spines relatively short for the genus, about equal in length, not exceeding the longest anal fin soft ray length)

Figures

FIG. 8. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Polydactylus approximans, 92 mm SL*; (B) Trinectes fonsecensis, 72 mm SL*; (C) Citharichthys gilberti, 64 mm SL*; (D) Pimelodella chagresi, 92 mm SL; (E) Rhamdia guatemalensis, 132 mm SL, (F) 132 mm SL; (G) Rhamdia laticauda, 109 mm SL; (H) Hypostomus aspidolepis, 98 mm SL, (I) 170 mm SL; (J) Rineloricaria uracantha, 120 mm SL; (K) Trichomycterus striatus, 75 mm SL*; (L) Synbranchus marmoratus, 120 mm SL*; (M) Pseudophallus elcapitanensis, 127 mm SL*; (N) Pseudophallus starksi, 118 mm SL. *Pictures taken after fixation in 10% formalin and stored in 70% alcohol.

FIG. 6. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Dormitator latifrons, 106 mm SL; (B) Eleotris picta, 136 mm SL, (C) 196 mm SL; (D) Eleotris tecta, 172 mm SL; (E) Gobiomorus maculatus, 108 mm SL, (F) 158 mm SL, (G) 161 mm SL; (H) Hemieleotris latifasciata, 59 mm SL; (I) Leptophilypnus panamensis, 47 mm SL*; (J) Awaous transandeanus, 94 mm SL, (K) 111 mm SL; (L) Ctenogobius sagittula, 118 mm SL*; (M) Sicydium salvini, 56 mm SL*, (N) 93 mm SL*, (O) mm SL 93 mm SL*, detail of the adhesive disc; (P) Dajaus monticola, 201 mm SL; (Q) Mugil setosus, 236 mm SL. *Pictures taken after fixation in 10% formalin and stored in 70% alcohol.

FIG. 2. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Atherinella argentea, 54 mm SL, (B) 64 mm SL*; (C) Brycon behreae, 139 mm SL, (D) 163 mm SL, (E) 227 mm SL; (F) Astyanax orstedii, 75 mm SL; (G) Odontostilbe dialeptura, 36 mm SL; (H) Pseudocheirodon terrabae, 44 mm SL; (I) Roeboides bussingi, 32 mm SL, (J) 91 mm SL, (K) 92 mm SL; (L) Cyphocharax magdalenae, 66 mm SL, (M) 81 mm SL; (N) Hoplias microlepis, 54 mm SL, (O) 80 mm SL*. *Picture taken after fixation in 10% formalin and stored in 70% alcohol.

FIG. 3. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Lebiasina boruca, 42 mm SL, (B) 87 mm SL; (C) Amphilophus lyonsi, 125 mm SL*, (D) 157 mm SL**; (E) Andinoacara coeruleopunctatus, 40 mm SL, (F) 59 mm SL, (G) 75 mm SL, (H) 83 mm SL*; (I) Cribroheros altifrons, 40 mm SL, (J) 119 mm SL, (K) 131 mm SL*; (L) Cribroheros diquis, 20 mm SL. *Pictures taken after fixation in 10% formalin and stored in 70% alcohol. **Specimen in captivity, picture for illustrative purposes.

FIG. 5. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Oxyzygonectes dovii, 98 mm SL, (B) 103 mm SL; (C) Brachyrhaphis roseni, 32 mm SL, (D) 36 mm SL; (E) Brachyrhaphis terrabensis, 39 mm SL, (F) 61 mm SL*; (G) Poecilia gillii, 72 mm SL, (H) 79 mm SL; (I) Poeciliopsis elongata, 84 mm SL; (J) Poeciliopsis paucimaculata, 62 mm SL; (K) Poeciliopsis retropinna, 38 mm SL, (L) 62 mm SL; (M) Poeciliopsis turrubarensis, 64 mm SL*; (N) Priapichthys panamensis, 40 mm SL*; (O) Cynodonichthys glaucus, 43 mm SL*; (P) Cynodonichthys hildebrandi, 63 mm SL*; (Q) Cynodonichthys uroflammeus, 37 mm SL. *Pictures taken after fixation in 10% formalin and stored in 70% alcohol.

FIG. 9. Frontal scalation patterns in members of Rivulidae from the Coto River basin, Pacific coast, Costa Rica, (A) D-type, (B) D-type. Adapted from Bussing (1998).

FIG. 4. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Cribroheros diquis, 76 mm SL, (B) 101 mm SL; (C) Oreochromis niloticus, 114 mm SL, (D) 204 mm SL; (E) Parachromis managuensis 72 mm SL, (F) 140 mm SL; (G) Talamancaheros sieboldii, 60 mm SL, (H) 79 mm SL, (I) 82 mm SL, (J) 153 mm SL, (K) Breeding pair, with young**. **Underwater picture.

FIG. 7. Fishes from the Coto River basin, Pacific coast, Costa Rica. (A) Oligoplites altus, 109 mm SL*; (B) Centropomus medius, 93 mm S*L; (C) Centropomus nigrescens, 113 mm SL*, (D) 170 mm SL; (E) Centropomus robalito, 131 mm SL*; (F) Diapterus peruvianus, 59 mm SL*; (G) Eucinostomus currani, 112 mm SL; (H) 15 mm SL*; (I) Eugerres brevimanus, 151 mm SL; (J) Rhonciscus bayanus, 128 mm SL*, (K) 221 mm SL; (L) Lutjanus argentiventris, 142 mm SL; (M) Lutjanus guttatus, 162 mm SL. *Pictures taken after fixation in 10% formalin and stored in 70% alcohol.