A Catfish of the Genus Trichomycterus from a Thermal Stream in Southern

Journal of Fish Biology (2007) 71, 1303–1316 doi:10.1111/j.1095-8649.2007.01589.x, available online at http://www.blackwell-synergy.com

A catﬁsh of the genus Trichomycterus from a thermal stream in southern South America (Teleostei, Siluriformes, Trichomycteridae), with comments on relationships within the genus

L. FERNA´ NDEZ*† AND G. MIRANDA‡ *Departamento Vertebrados, Instituto Miguel Lillo, Miguel Lillo 251, 4000 Tucuman,´ Argentina and ‡Instituto de Ecologı´a, Universidad Mayor de San Andres, Bolivia, CP 10077, La Paz, Bolivia

(Received 16 June 2005, Accepted 23 May 2007)

The first record of two trichomycterid species from the thermal waters of a small stream in Miraflores, north of Potosı´ , Bolivia is given. The reported species are Trichomycterus therma n. sp. and Trichomycterus tiraquae. The new species differ from all congeners in the possession of thickened transverse skin on the ventral surface of the head. They are further distinguished from all congeners by the following combination of characteristics: presence of spatulate incisiform premaxillary teeth; presence of large and rounded papilla-like structures on trunk of body; continuous segment of the laterosensory canal within the frontal with the presence of a segment between pores 2 and 6; long laterosensory canal with four to six pores; maxilla with a short anterior process that is smaller than the main axis of the bone, and has an anterior orientation; mesethmoid shaft narrower than the width of the lateral cornua; prepelvic length 58 7–61 0% of Á Á standard length (L ); head width 19 1–22 8% of L ; submaxillary barbel length 23 9–37 5% of S Á Á S Á Á head length (LH). Two derived characters, namely the presence of spatulate incisiform premaxillary teeth and large and rounded papilla-like structures, define a monophyletic group within Trichomycterus, comprising T. therma, T. corduvensis and T. tiraquae. # 2007 The Authors Journal compilation # 2007 The Fisheries Society of the British Isles

Key words: Bolivia; catﬁshes; new species; thermal water.

INTRODUCTION The genus Trichomycterus is the largest non-monophyletic assemblage in the Tri- chomycteridae, and its taxonomy requires a comprehensive revision (Fernan´ dez & Schaefer, 2005). Trichomycterus has >100 recognized species that inhabit a diver- sity of habitats from Amazonian lowlands to the Andean cordilleras (Arratia, 1998; de Pinna, 1998). Seven or eight species of Trichomycterus occur in the western region of Bolivia (Eigenmann, 1918; Terrazas Urquidi, 1970; Arratia & Menu-Marque, 1984; Ferna´ ndez, 2000a, 2001; Ferna´ ndez & Osinaga, 2006).

†Author to whom correspondence should be addressed at present address: Division of Vertebrate Zoology, Department of Ichthyology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, U.S.A. Tel.: 1 212 769 5797; fax: 1 212 769 5642; þ þ email: [email protected] 1303

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Trichomycterus shows a high potential for colonization of extreme environ- ments such as high altitude (>4000 m), subterranean streams, island fresh waters (56 km off the Colombian coast) and, as reported in this study, warm thermal waters (>35° C) (Pouilly & Miranda, 2003; Fernandez´ & Schaefer, 2005). The Andean and Preandean regions are characterized by the presence of several endorrheic drainage basins, each of which has evolved a characteristic fish fauna with some of them poorly known or hitherto inaccessible (Arratia & Menu-Marque, 1984; Fernandez´ & Vari, 2000, 2002; Fernandez´ & Schaefer, 2003). The environmental impacts of gold-mining activities in these regions include deforestation and the release of thousands of tonnes of sediment and chemicals into exploited rivers (e.g. >330 t of mercury released since 1952 according to Maurice-Bourgoin & Quiroga, 2002), and these impacts endanger many populations of endemic species of Trichomycterus. This study presents a description of a new species of Trichomycterus, found with Trichomycterus tiraquae (Fowler) in a thermal stream at the locality of Miraflores, near the city of Potosı´, in Bolivia. De Pinna & Wosiacki (2003) placed T. tiraquae in synonymy with Trichomycterus rivulatus Valenciennes but this is disputed (L. Fernan´ dez, pers. obs.). This study represents the first record of species of Trichomycteridae known to inhabit thermal waters.

MATERIALS AND METHODS

STUDY AREA Miraflores has a complex of thermal streams (19°279 S; 65°479 W) in Potosı´ Depart- ment, Bolivia. It lies in the ‘Ecoregion of the Vertiente Oriental, Valles interandinos: Prepuna’ (Gerold, 2003), within the Austral biogeographic region. The study area is characterized by a subtropical climate. The annual average air temperature ranges from 14 to 16° C and the annual average precipitation ranges from 100 to 400 mm (Gerold, 2003). The Potosı´ area is crossed by several parallel streams running eastwards to join the Rı´ o Tarapaya, a tributary of the Rı´ o Pilcomayo. The new species was collected in an unnamed thermal stream that originates from sub-Andean mountains and flows as a small watercourse 800 m in length with four waterfalls of 7 to 9 m height each. The fishes of interest occur 500 m downstream from the thermal source at a site where water temperature is 37° C. This contrasts with the Rı´ o Tarapaya, where the water temperature is 12 to 18° C. Fishes were collected using backpack electrofishing gear delivering a current between 300 and 600 V and quickly killed by stunning. Individuals were preserved in buffered formaldehyde (4%) before transport to the laboratory. Water temperature was mea- sured with a WTW digital thermometer and pH with a Hach apparatus. Measurements were taken on the left side of each specimen with digital callipers under a stereomicro- scope, and followed the methods of Tchernavin (1944) and de Pinna (1992). Cleared and double-stained osteological preparations (denoted C&S) of comparative material follow Taylor & Van Dyke (1985), and some type specimens were studied from radiographs. Osteological terminology follows Baskin (1973) and de Pinna (1989, 1998), and the numbering system and terminology for the laterosensory pores of the head follow Arratia & Huaquin (1995) and Arratia (1998). Counts of dorsal and anal-fin rays and vertebrae follow de Pinna (1992) with vertebral counts omitting the compound vertebrae of the Weberian complex and the vertebrae associated with the caudal skeleton. Counts of caudal vertebrae follow Fernand´ ez & Schaefer (2003). Institutional abbreviations follow Leviton et al. (1985), with the addition of FLBS, Flathead Lake Biological Station, Montana; IBA, Instituto de Biologı´ a Animal, Mendoza, Argentina; MFA-ZV, Museo Provincial de Ciencias Naturales Florentino Ameghino, Santa Fe, Argentina.

Comparative material examined in this study is that cited in Fernandez´ (2000b) and Fernan´ dez & Vari (2000, 2004) with the addition of specimens listed below. Trichomycterus aguarague Fernandez & Osinaga MNKP 4002, paratypes, six specimens (1 C&S), 28 7–56 1 mm standard length (LS), Bolivia, Tarija, Gran Chaco, Rio Caiguami, 9 MarchÁ 2003,Á coll. Osinaga, Coro. Trichomycterus alterus (Marini, Nichols & La Monte) FML 2085, nine specimens (C&S), 43 6–49 1 mm LS, Argentina, Catamarca, San Blas, Andalucas, 7 September 1994, coll. FernÁ a´ ndeÁz, Scrocchi, Montero; FML 2088, four specimens (2 C&S), 40 8–42 1 mm LS, Argentina, Catamarca, Paclıń, Rıó Paclıń, 16 September 1994, coll. FernÁandez,´ Á Scrocchi, Montero. Trichomycterus barbouri (Eigenmann) CAS 64578, paratype, one specimen, 29 5 mm L , Bolivia, Rı´ o Beni, coll. Barbour; Á S USNM 120289, paratypes, four specimens, 27 8–29 7 mm LS, Bolivia, Alti Beni. Tricho- mycterus belensis Fernandez´ & Vari FML 2531,Á paratypes,Á 10 specimens (2 C&S), 25 5– Á 58 7 mm LS, Argentina, Catamarca, Belen, Laguna Blanca, 8 September 1993, coll. FernÁ andez,´ Scrocchi, Lavilla. Trichomycterus corduvensis Weyenbergh FML 1215, four specimens, 39 0–93 1 mm L , Argentina, Tucuman, Trancas, Rı´ o Vipos, 25 July 1985, Á Á S coll. Pagaburo; FML 1796, four specimens (2 C&S), 26 6–57 9 mm LS, Argentina, Tucuman, Yerba Buena, Rı´ o Muerto, 5 October 1992, coll.ÁFernandez,Á´ Scrocchi, Lobo. Trichomycterus chaberti Durand USNM 236426, two specimens, 64 2–83 8 mm LS, Bolivia, Potosı´ , Cave Toro Toro, 31 August 1982, coll. Morales. TrichomycterusÁ Á gorgona Fernandez & Schaefer ANSP 149946 holotype (radiographs), 63 6 mm LS, Colombia, Cauca, Isla Gorgona, 21 September 1961; ICN-MHN 10019 paratype,Á one specimen, 58 7 mm L , Colombia, Cauca, Isla Gorgona, 21 September 1961. Trichomycterus pseu- Á S dosilvinichthys Fernandez & Vari FML 2588, holotype, 61 1 mm LS, Argentina, La Rioja, Chilecito, Rı´ o Amarillo, 8 September 1994, coll. FernÁandez,´ Scrocchi, Montero; FML 2589, paratypes, nine specimens (C&S), 54 5–62 2 mm LS, Argentina, La Rioja, Chilecito, Rı´ o Amarillo, 8 September 1994, coll. FernÁ andez,´ Á Scrocchi, Montero. Tricho- mycterus punctulatus Valenciennes FMNH 58672, paratype, one specimen, 97 8 mm L , Á S Peru.´ T. rivulatus MNHNC 2347, two specimens, 86 9–90 1 mm LS, Chile, Parinacota, Arica, 30 Abr 1979, coll. Gallardo. T. tiraquae ANSPÁ 69127,Á paratypes, two specimens, 27 7–32 6 mm LS, Bolivia, Cochabamba, Tiraquae, 30 September 1937, coll. Carriker, Howes;Á ÁMUSM 15476, three specimens, 58 7–60.1 mm L , Bolivia, Potosı´ , Rı´ o Tupiza; Á S CBF uncat., two specimens, 38 7–49 9 mm LS, Bolivia, Potosı´, Rıó Pilcomayo, 20 October 2001, coll. G. Miranda. RhizosomicÁ Áhthys totae (Miles) SU 37074 paratypes, two specimens (radiographs), 84 6 mm LS (not good condition), Colombia, Boyaca, Lago Tota, 18 February 1942, coll.Á Miles, Winz; USNM 120130, four specimens, 104 9–130 1 mm Á Á LS, Colombia, Boyaca, Lago Tota, 1 February 1942, coll. Ubidia.

RESULTS

TRICHOMYCTERUS THERMA N. SP. Holotype CBF 8886, 35 4 mm L , Bolivia, Departamento Potosı´ , Pilcomayo-Parana´ basin, Á S Rı´ o Tarapaya drainage, near Ban˜ os Termales Miraﬂores (19°279 S; 65°479 W), elevation 3600 m, collected by G. Miranda and R. Marin, October 2001 (Fig. 1).

Paratypes CBF 9099, three specimens, 33 5–58 4 mm LS (38 0 mm LS C&S), same data as holotype. Á Á Á

Diagnosis Trichomycterus therma n. sp. is readily distinguished from all other congeners from western and southern South America by having an autapomorphic

# 2007 The Authors Journal compilation # 2007 The Fisheries Society of the British Isles, Journal of Fish Biology 2007, 71, 1303–1316 1306 L . F E R N A´ N D E Z A N D G . M I R A N D A

FIG. 1. Trichomycterus therma, holotype, CBF 8886, 35 4 mm standard length. Á thickened transverse skin on the ventral surface of the head (Fig. 2). It is further distinguished from other congeners with the exception of T. corduvensis from Argentina and T. tiraquae from Bolivia by the combination of the following characters: presence of spatulate incisiform premaxillary teeth [Fig. 3(a)]; presence of large and rounded papilla-like structures on the trunk of the body; the continuous segment of the laterosensory canal within the frontal with the presence of a segment between pores 2 and 6; and laterosensory canal on trunk with 4 to 6 pores. Trichomycterus therma n. sp. can be distinguished from T. tiraquae and T. corduvensis by: the shape of the maxilla, which has a short anterior process that is shorter than the main axis of the bone and is anteriorly oriented [Fig. 4(a)] [v. anterior process enlarged and equal to, or longer than the main axis of the bone and with an anterolateral orientation, Fig. 4(b)]; mesethmoid shaft narrower than the width of the lateral cornua [Fig. 5(a)] [v. shaft equal to or wider than width of lateral cornua, Fig. 5(b)]. Trichomyc- terus therma n. sp. can also be distinguished from T. tiraquae by: the prepelvic length 58 7–61 0% of LS (v. 56 6–57 6); the head width 19 1–22 8% of LS (v. 17 4–18Á 9); theÁ submaxillary barbelÁ Á length 23 9–37 5% of LÁ (v. Á43 3–54 8). Á Á Á Á S Á Á

Description Morphometric data for holotype and paratype given in Table I. Body elongate, cylindrical; trunk region compressed, becoming progressively more compressed towards caudal fin. Dorsal profile of trunk convex. Ventral profile of trunk and caudal peduncle nearly straight. Greatest body depth at mid-trunk region, depth uniform from posterior of base of dorsal fin to caudal fin. Anus

FIG. 2. Trichomycterus therma, holotype, CBF 8886, 35 4 mm standard length, ventral view of the head Á showing details of the autapomorphic thickening of the skin ( ).

FIG. 3. Internal view of premaxillary teeth: (a) Trichomycterus therma, paratype, CBF 9099, 38 0 mm Á standard length (L ) and (b) T. ramosus FML 2071, 54 2 mm L . S Á S located approximately midway between pelvic-ﬁn insertion and anal-ﬁn origin. Numerous large and rounded papilla-like structures present on skin of trunk. Head wide and depressed; trapezoidal in dorsal view and wider posterior than anteriorly. In ventral view, thickened transverse skin on the ventral surface of the head (Fig. 2). Eyes located on dorsal surface of head, ovoid.

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FIG. 4. Dorsal view of maxilla: (a) Trichomycterus therma, paratype, CBF 9099, 38 0 mm standard length Á (L ) and (b) T. corduvensis FML 1796, 33 5 mm L . S Á S

Skin covering eyes thin, transparent and separated from surface of eyeball; orbital margin not free. Anterior naris slightly smaller than posterior naris, surrounded medially by fleshy flap of integument and laterally by barbels. Posterior naris partially surrounded anteriorly by flap of thin skin. Infraorbital canal discontinuous with two segments. Anterior segment bearing infraorbital pores 1 and 3, separated from posterior segment behind eye bearing infraorbital pores 10 and 11. Supraorbital canal continuous and with three pores: 1, 2 and 6. Epiphyseal branch of supraorbital canal discontinuous with pair of median pores (pore number 6) posterior to eyes. Mandibulo- preopercular canal represented by reduced preopercular canal bearing single pore on skin surface. Laterosensory canal along trunk of body not reduced, with four to six pores on anterior portion of lateral line. Posterior terminus of canal located at vertical through middle of pectoral-fin base. Frontolachrymal tendon bone compact, cylindrical, with lateral expansion absent. Lachrymal- antorbital small, tube-like ossicle, twice the length of maxilla. Mouth subterminal, rictus directed posterior. Mesethmoid T-shaped, elongate with anterior margin concave and shaft narrower than the width of the lateral cornua [Fig. 5(a)]. Premaxilla rectangular and larger than maxilla. Pre- maxilla with four or five rows of teeth; outer row with 13 or 14 spatulate incisiform teeth [Fig. 3(a)]. Maxilla enlarged, L-shaped and smaller than premaxilla. Maxilla with pair of condyles projecting between premaxilla and anterior border of palatine. Maxilla has a short anterior process that is shorter than

FIG. 5. Dorsal view of mesethmoid: (a) Trichomycterus therma, paratype, CBF 9099, 38 0 mm standard Á length (L ) and (b) T. corduvensis FML 1796, 33 5 mm L . S Á S the main axis of the bone and is anteriorly oriented [Fig. 4(a)]. Posterior process of maxilla broad and short. Palatine rectangular and broad anteriorly with short posterior process situated dorsal to broad metapterygoid. Palatine artic- ulates medially with both vomer and lateral ethmoid. Lower lip with moderate ﬂeshy lobes along lateral margin; lobes situated mesial to base of rictal barbel. Lips and barbels covered by papillae. Barbels elongate, not thread-like or distally branching. Tips of maxillary barbels extending posterior to close to interopercular odontodes, but not extending to posterior margin of pectoral ﬁn. Nasal barbels slender, extending posterior beyond posterior margin of eye. Submaxillary

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TABLE I. Morphometric data for the holotype and paratypes [n 3, including one cleared and double-stained osteological preparations (C&S)] of Tric¼homycterus therma, new species

Holotype Paratypes C&S

Standard length (L ; mm) 35 4 33 5 58 4 43 8 S Á Á Á Á Total length (mm) 41 8 39 3 67 1 50 4 Á Á Á Á Percentages of LS Body depth 17 0 13 0 14 6 13 7 Á Á Á Á Caudal peduncle length 21 9 18 1 20 5 20 5 Á Á Á Á Caudal peduncle depth 11 9 10 1 10 8 10 8 Á Á Á Á Predorsal length 63 6 62 4 62 8 62 4 Á Á Á Á Preanal length 73 0 72 6 76 9 75 2 Á Á Á Á Prepelvic length 59 2 58 7 61 0 59 1 Á Á Á Á Dorsal-fin base length 12 7 11 7 12 9 12 1 Á Á Á Á Anal-fin base length 7 2 7 8 8 2 7 9 Á Á Á Á Head length 23 0 19 9 22 7 20 5 Á Á Á Á Head width 22 8 19 1 21 1 19 6 Á Á Á Á Head depth 12 5 10 7 11 4 11 2 Á Á Á Á Head length (L ; mm) 8 1 7 6 11 6 9 0 H Á Á Á Á Percentages of LH Nasal barbel length 54 2 38 3 48 1 46 4 Á Á Á Á Maxillary barbel length 54 9 52 6 63 9 61 1 Á Á Á Á Submaxillary barbel length 37 5 23 9 31 3 27 7 Á Á Á Á Mouth width 44 2 43 3 49 9 49 2 Á Á Á Á Snout length 46 7 49 5 50 1 49 7 Á Á Á Á Interorbital width 31 2 32 5 36 7 33 7 Á Á Á Á barbels shorter than maxillary barbels. Six branchiostegal rays. Interopercular patch of odontodes anteroposteriorly elongate, with 20 to 27 odontodes. Oper- cular patch of odontodes small, rounded, with 12 to 18 odontodes. Poster- dorsal process of operculum elongate. Pectoral-fin rays i,8; posterior margin of fin straight with first ray not extending beyond fin margin. Pectoral girdle composed of large, triangular cleithrum- coracoid and one triangular, ossified proximal radial. Dorsal-fin rays v,9 in cleared and stained specimens; 8 branched and 1 unbranched rays externally visible, with remaining fin rays hidden under thick integument that overlies anterobasal portion of fin; posterior fin margin straight; fin origin situated posterior to vertical through anus; rays supported internally by nine pterygiophores, all of similar length, except last element slightly shorter and square-shaped distally. Anal-fin rays vi,5; 5 branched and 1 unbranched rays externally visible, with remaining fin rays hidden under thick integument that overlies anterobasal portion of fin. Distal margin of anal fin slightly rounded; fin origin situated posterior to vertical through one or two posterior most dorsal-fin rays. Anal- fin rays supported internally by six pterygiophores. All pterygiophores of similar length, with last square-shaped distally. Pelvic basipterygium bears two anterolateral processes; narrow from base to distal tip. Pelvic radials absent. Pelvic-fin rays i,4 plus one splint, with second and third rays longest. Tip of

# 2007 The Authors Journal compilation # 2007 The Fisheries Society of the British Isles, Journal of Fish Biology 2007, 71, 1303–1316 N E W S P E C I E S O F C A T F I S H F R O M T H E R M A L W A T E R S 1311 addressed pelvic fin extending posterior beyond anus, but falling short of anal- fin origin. Caudal fin with 13 principal rays (three rays on hypural 3, three on hypurals 4 5; and seven on hypurals 1 2 parahypural); caudal- fin margin straight.þDorsal procurrent rays 12 andþ ventralþ procurrent rays 12. Caudal skeleton with neural spine of preural centrum 1 reduced, epural oval. Hypural 3 separate from hypurals 4 and 5 and hypurals 1 and 2 fused to parhypural. Total vertebrae 32 (eigth precaudal, 24 caudal vertebrae). First dorsal-fin pterygiophore inserts posterior to neural spine of vertebra 16; first anal-fin pterygiophore inserts posterior to haemal spine of vertebra 20; no overlap between last dorsal- and first anal-fin pterygiophores. Thirteen vertebrae between last pterygiophore of dorsal fin and first preural centrum. Eleven vertebrae between last pterygiophore of anal fin and first preural centrum. Twelve paired ribs; first pair compact and strong; remaining ribs slender and longer posteriorly.

Colour in alcohol Trichomycterus therma n. sp. demonstrates a faint marmoration formed by patches of small dark chromatophores on head and body (Fig. 1). Ventral surface of the head varies between specimens from lightly pigmented to hyaline. All barbels pigmented faintly but opercular and interopercular odontodes and oral dentition unpigmented. Dorsal, anal and pectoral fins with irregular dark pigmentation on rays and membranes. Caudal fin with irregular dark pigmentation on membranes, darker than other unpaired fins. Pelvic fin ranging from lightly pigmented to hyaline.

Ecology Trichomycterus therma n. sp. inhabits a slightly sloping stream that arises from a spring and runs a short distance before emptying into the Rı´ o Tarapaya (Pilcomayo-Parana´ basin) at an elevation of c. 3600 m a.s.l. (Fig. 6). The clear water stream ranges between 1–1 5 m in width and 0 15–0 5 m in depth, and Á Á Á runs over clay and rock-pebble substrata with algae. This area has high geo- thermal activity. At the spring source, the water emerges at 50 to 60° C into a small pool, which drains c. 400 m away from the source into the stream where water temperature cools down to 37° C. The fishes occur mainly in the area where the water is 37° C and has a pH of 8 2. Prior to this study, three specimens had been opened ventrally, allowing analysisÁ of the stomach contents. The stomach contents of these three specimens consisted mainly of Diptera (mostly Chironomidae) and Coleoptera (Elmidae). Dipterans were the predominant group with a relative abundance of 95%. The diet of benthic macro-invertebrates in T. therma n. sp. is common to that of many congeners (Fernandez´ & Vari, 2000, 2002). The only other species of vertebrate collected at that site was T. tiraquae. The only previous reference of a fish species inhabiting thermal waters close to Miraflores is provided by a record of 16 species (Characidae, Crenuchidae, Parodontidae, Erythrinidae, Loricariidae and Cichlidae) collected from Aguas Calientes at an elevation of 500 m [Jujuy Prov- ince, north-western Argentina 23°449 S; 64°389 W (Menni et al., 1998)]. The waters of Aguas Calientes have a pH of 8 40, and the temperature ranges from Á

# 2007 The Authors Journal compilation # 2007 The Fisheries Society of the British Isles, Journal of Fish Biology 2007, 71, 1303–1316 1312 L . F E R N A´ N D E Z A N D G . M I R A N D A

FIG. 6. Maps showing the type locality of Trichomycterus therma, new species. Inset box at upper left shows outline of Bolivia, and Tarapaya River collection region in small box; scale in km. Main map shows collection region with latitude and longitude co-ordinates, and capture site (Miraﬂores) in small box. Inset boxes at upper right show Miraﬂores capture site in greater detail.

23 to 59° C (Menni et al., 1998). Other reports of ﬁsh species inhabiting thermal waters in southern South America are for Barreto, Co´ rdoba Province (two thermal springs with water temperature 28 and 32° C) and Arroyo Valcheta, in northern Patagonia (water temperature from 18 to 22 6° C) (Menni et al., Á 1998; Menni, 2004). The distribution of T. therma n. sp. and T. tiraquae in a thermal water stream contrasts with the statement made by Menni et al. (1998:279), who suggested that the absence of Trichomycterus in Aguas Calientes could be because of the high water temperature. The ichthyofauna of Miraﬂores is apparently depauperate (two species v. 16) based on sampling of Aguas Calientes.

Distribution Trichomycterus therma n. sp. is known solely from the type locality situated within the limits of the man-made thermal bath of Miraﬂores, in the northern portion of the Department of Potosı´ , Bolivia.

Etymology The speciﬁc name, therma (meaning ‘hot’, from the Greek city of Therma, known for its hot springs), is in reference to the habitat of the new species in thermal water, treated as a noun in apposition.

DISCUSSION A resolution of the phylogenetic relationships within Trichomycterus represents a formidable challenge. Initial forays in this endeavour (Costa & Bockmann, 1993) represent the ﬁrst steps in revising the apparently paraphyletic Trichomycterus into several monophyletic groups clearly deﬁned by synapomorphies. In this section, preliminary evidence is discussed that bears on the phylogenetic relationships of T. therma n. sp. and relationships among species within the Tricho- mycterinae. Two derived characters that delimit a monophyletic assemblage within Trichomycterus are proposed. The possession of spatulate incisiform premaxillary teeth [Fig. 3(a)] is proposed as a derived condition shared by T. therma n. sp., Trichomycterus duellmani Arratia & Menu-Marque (Arratia & Menu-Marque, 1984), Trichomycterus spegazzinii (Berg), Trichomycterus borellii Boulenger, Trichomycterus corduvenis Weyenbergh and T. tiraquae (Fernandez,´ 1999, 2001). This condition contrasts with the conic or narrow incisiform teeth [Fig. 3(b)] widely distributed among species of Trichomycterus [e.g. Trichomycterus roigi Arratia & Menu-Marque and Trichomycterus boylei (Nichols) (Arratia & Menu-Marque, 1984; Fernan´ dez, 1999), T. punctulatus, Trichomycterus laucaensis Arratia and Trichomycterus chungaraensis Arratia (Arratia, 1983), T. barbouri (Fernan´ dez, 2000a), T. rivulatus (Eigenmann, 1918), Trichomycterus areolatus Valenciennes, Trichomycterus chiltoni (Eigenmann), Trichomycterus oroyae (Eigenmann & Eigenmann), Trichomycterus quechuorus (Steindachner), Trichomycterus atochae (Allen), Trichomycterus heterodontus (Eigenmann) and Trichomycterus tenuis Weyenbergh (Fernandez,´ 1999), Trichomycterus catamarcensis Fernandez´ & Vari (Fernandez´ & Vari, 2000), Trichomycterus ramosus Fernandez´ (Fernandez,´ 2000b), T. alterus and T. belensis (Fernandez,´ 1999; Fernandez´ & Vari, 2002), Trichomycterus yuska Fernandez´ & Schaefer (Fernandez´ & Schaefer, 2003), T. pseudosilvinichthys (Ferna´ ndez & Vari, 2004), T. aguarague (Fernandez & Osinaga, 2006)], plus the out-group Copionodon, Trichogenes and the trichomycterine genera Bullockia (Arratia et al., 1978), Eremophilus, Silvinichthys (Arratia et al., 1978; Arratia, 1998; Fernandez,´ 1999; Fernandez´ & de Pinna, 2005), Hatcheria (Arratia & Menu-Marque, 1981) and Rhizosomichthys (pers. obs.). The derived presence of large and rounded papilla-like structures in T. therma n. sp. is shared by T. tiraquae and T. corduvensis (Ferna´ ndez, 1999, 2001). Small and conic papillae are present in most species of Trichomycterus [e.g. T. roigi and T. duellmani (Arratia & Menu-Marque, 1984), T. laucaensis and T. chungaraensis (Arratia, 1983), T. barbouri (Fernandez,´ 2000a), T. areolatus, T. chiltoni, T. rivulatus, T. punctulatus, T. oroyae, T. quechuorus, T. atochae, T. spegazzinii, T. boylei, T. borellii, T. heterodontus, T. ramosus (Fernandez,´ 2000b), T. catamarcensis (Fernandez´ & Vari, 2000), T. alterus and T. belensis (Fernandez,´ 2001; Fernandez´ & Vari, 2002), T. yuska (Fernandez´ & Schaefer, 2003), T. pseudosilvinichthys (Fernandez´ & Vari, 2004)], and the outgroups Copionodon,

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Trichogenes, Eremophilus, Bullockia, Hatcheria (Arratia et al., 1978; Arratia & Menu-Marque, 1981) and Rhizosomichthys (pers. obs.). Based on this small sampling of derived character states, it is possible to raise a preliminary phylogenetic hypothesis for further testing. It appears that T. therma n. sp. is more closely related to T. duellmani, T. spegazzinii, T. borellii, T. tiraquae and T. corduvensis than to other Trichomycterus species or Tricho- mycterinae and within that group to T. tiraquae and T. corduvensis. Nearly all fish have internal body temperatures that approximate external water temperatures, thus profound changes in physiology accompany environmental temperature changes, and death occurs quickly outside tolerance limits (Matthews, 1998). Very few fishes can tolerate exposure to water temperature >40° C, and for many North American freshwater fishes, the critical thermal maximum (CTM) is from c. 32 to 38° C. Proteins denature at extreme high temperatures, limiting nearly all fishes to temperatures c. <44° C. The record for high temperature for thermal tolerance of any fish species was reported for the sheepshead minnow Cyprinodon variegatus Lacepe` de, with a CTM of 45 1° C for individuals acclimated at 37–42° C (Matthews, 1998). Trichomycterus Á therma n. sp. and T. tiraquae live within this range (28 to 37° C). The occurrence of T. therma n. sp. and T. tiraquae in the thermal stream at Miraflores is of conservation importance. The stream, which currently represents the entire known range of T. therma n. sp., is facing increasing exploitation through tourism (pers. obs.).

We thank S. Schaefer, B. Brown, A. Aquino, D. Rodriguez, R. Arrindell (AMNH), J. Lundberg, M. Sabaj (ANSP), J. Sarmiento (CBF), W. Eschmeyer, D. Catania (CAS), M. Rogers, B. Chernoff (FMNH), E. Wiley, A. Bentley (KU), L. Malabarba, R. Reis, J. da Silva (MCP), K. Hartel (MCZ), H. Ortega, M. Velasquez (MUSM), M. de Pinna, J. de Figueiredo, O. Oyakawa (MZUSP), D. Nelson (UMMZ), R. Marin (UMSA), R. Vari, L. Palmer, S. Raredon (USNM) and H. Wilkens (ZMH), for the loan of specimens, and assistance during visits to their institutions. This study was supported by the Instituto de Ecologia from Universidad Mayor de San Andres. Figs 3, 4 and 5 were prepared by N. Perez Carbajal. This paper beneﬁted from the comments and sugges- tions of R. Vari, I. Harrison and two anonymous reviewers.

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