Two new ornamental loricariid catfishes of Baryancistrus from rio Xingu drainage ( Siluriformes : Hypostominae )

Two new species of the hypostomine genus Baryancistrus are described from the rio Xingu drainage. Baryancistrus xanthellus is distinguished from all other Baryancistrus species by the presence of yellow spots along the entire body and conspicuous yellow marks on distal tip of dorsal and caudal fins. Baryancistrus chrysolomus is distinguished from its congeners by its uniform dark body coloration and presence of yellow bands on dorsal and caudal fins. Despite the lack of formal description, these species are very popular in the international aquarium trade. We expect that these formal descriptions might contribute to the improvement of Brazilian regulations in the international trade of ornamental loricariids.


Introduction
The loricariid genus Baryancistrus Rapp Py-Daniel, 1989 currently comprises four species: B. niveatus (Castelnau, 1855), the type species of the genus described from the rio Araguaia, Brazil, B. longipinnis (Kindle, 1895) from rio Tocantins, Brazil, B. demantoides Werneke, Sabaj, Lujan &Armbruster, 2005, andB. beggini Lujan, Arce &Armbruster, 2009 both from the area of confluence of ríos Orinoco and Ventuari in Venezuela and Colombia.This genus is characterized by a heavy and robust head and body, presence of strong odontodes on the cheek plates, numerous teeth, large and parallel disposed maxillae, and almost complete abdominal plating (Rapp Py-Daniel, 1989;Werneke et al., 2005;Lujan et al., 2009).All these features are overwhelmingly present in other loricariids, from which Baryancistrus is distinguished by the presence of a hypertrophied membrane posterior to the last branched dorsal-fin ray.This membrane can reach the supporting plate of the adipose fin or not, different from the genera Oligancistrus, Parancistrus, and Spectracanthicus in which the dorsal fin is completely connected to the adipose fin.Other than that, Baryancistrus can be easily misidentified as a Hemiancistrus, but the latter lacks the developed membrane (see Werneke et al., 2005 for main differences between Hemiancistrus and Baryancistrus).
Baryancistrus catfishes are very popular in aquarium fish trade due to their very attractive color pattern of clear and bright spots or marks over a dark background.Several undescribed Baryancistrus species are still being exported to US, Europe, and Asia and it has been strongly recommended by the Brazilian Environmental Agency (IBAMA) that these species should receive a formal description as soon as possible to avoid misidentifications and inflated prices.The absence of a formal name for these and other loricariid species motivated the adoption of a code system composed by letters and numbers (known as the "L-numbers" of DATZ magazine).In that system, two undescribed Baryancistrus species from rio Xingu in Brazil are included in the international aquarium trade: one species variably referred as "golden nugget pleco" (under codes L18 and L85 to juvenile and adult forms, respectively) and "Iriri golden nugget pleco" (L177), while the other is referred to as "mango pleco" under code L47.These two catfishes are herein described and some information on their ecology and behavior are provided.

Material and Methods
Measurements were made with digital calipers to the nearest 0.1 mm.All measurements and counts were taken in the left side, unless the structure was missing or damaged.Counts and measurements follow Armbruster (2003) and Oliveira et al. (2010).Counts included: number of plates between the extended dorsal fin membrane and supporting plate of the adipose fin and number of plates in the caudal peduncle.Museum acronyms follow Reis et al. (2003).Predorsal area reduced, with only one pair of small, separated diamond-shaped plates anterior to nuchal plate.

Color based differential key of
Mouth wide; lips large, covered with small round papillae except on area around maxillae.Maxillary barbel thick and short.Branchial opening moderate, wider in larger specimens.Interbranchial distance approx.56.5% in head length.
Head and body completely covered by large plates dorsally, except dorsal-fin base.Ventral surface largely unplated from snout to anal fin; in larger specimens, presence of two or three minute round plates close to insertion of pectoral spine or urogenital opening.Twenty-two perforated median plates, 23 lateral plates; four oblong plates on caudalfin base.All plates marked with lines of odontodes.Numerous hypertrophied odontodes only on evertible cheek plates, well developed in larger specimens with largest odontode reaching posterior end of first lateral plate.Ventral border of opercle with series of strong but short odontodes on probably mature males.
Dorsal fin II,7; spinelet present and dorsal-fin locking mechanism functional.Dorsal fin long and low, reaching adipose spine on small specimens when adpressed.Dorsalfin posterior membrane covering four plates immediately behind last dorsal-fin ray, but not reaching preadipose plate.Adipose fin large and with posterior membrane slightly developed.One single plate separating dorsal from preadipose plate.Caudal fin i,14,i, emarginated.Pectoral fin I,6, large, reaching well beyond posterior end of pelvic-fin base when adpressed.Pectoral fin covered by large odontodes on (possibly mature) males.Pelvic fin i,5 reaching posterior end of anal fin base when adpressed.Anal fin i,4, very reduced.All simple first rays covered by numerous short odontodes on their free surface.
Teeth long and deeply cuspidate.Cusps round and similar in larger specimens with vertical divide between cusps; in smaller specimens cusps are largely asymmetrical, with internal cups larger.Premaxilla and dentary of similar size and disposed in parallel to anterior border of snout.Modal number of premaxillary teeth 32; dentary teeth mode 46 (range of number of mandibulary teeth in Table 1).Buccal papilla long and digitiform.Color in life.Overall body color dark brown at dorsum and sides, paler on abdomen.Numerous bright, similar-sized yellow spots over head, body, dorsal, adipose, and caudal fins, and on dorsal surface of pectoral and pelvic fins.Yellow spots almost size of pupil in juveniles, becoming proportionally smaller, more numerous and somewhat paler in adults.Young specimens with wide yellow band on distal third of caudal and dorsal fin; dorsal-fin band larger anteriorly, becoming gradually slender posteriorly.In adults, bands on fins become reduced to spots on anterior distal ends of dorsal and caudal fins (Fig. 2).Considerable variation in density and size of spots.
Color in alcohol.Similar to pattern described for living specimens but with ground color brown to dark olive and white to cream markings (Fig. 1).
Distribution.This species has been recorded from the area called Volta Grande do rio Xingu, an area immediately above Belo Monte falls, and from rio Iriri, the larger tributary of rio Xingu (Figs. 3 and 4a).
Etymology.From the Greek xanthellus, yellow, in allusion to the bright color of the specimens.A noun in apposition.Zuanon, 1999).Occasional bryozoans and chironomid larvae were also found.Underwater observations indicate that the food is scraped from the surface of submerged rocks by gently combing the periphyton cover with the numerous and tightly spaced teeth (JZ, pers.obs.).Description.Morphometrics and meristics in Table 1.Medium-size loricariids; bigger specimen examined reached 219.0 mm SL.Very similar to preceding species.Body short and robust, deep.Profile from snout to eye strongly sloped, gently convex from eye to insertion of dorsal fin due to prominence of supraoccipital process.Profile strongly inclined from dorsal-fin insertion to caudal fin.Body deepest between supraoccipital and dorsal-fin insertion.Ventral surface flat and straight from snout tip to caudal-fin base.Snout with low vertical ridge conspicuously covered by a series of smaller plates.Anterior lateral plates gently bent; low ridge along dorsal fin until base of adipose fin.Anterior portion of body half oval in cross section, triangular at caudal peduncle.

Baryancistrus chrysolomus,
Head large and wide; snout round in dorsal view.Eye large and round, iris operculum present.Orbit not elevated; interorbital area flat.No ridge between eyes and nares.Supraoccipital process not elevated, almost indistinct from rest of bone, round posteriorly and elevated.Supraoccipital limited by a pair of large quadrangular plates tightly connected.Predorsal area reduced, with one pair of separated diamondshaped plates anterior to nuchal plate.Mouth wide; lips large with small round papillae except around maxillae.Maxillary barbels slender and short.Branchial opening moderate, wider in larger specimens.Interbranchial distance large approx.57.7% in head length.
Head and body completely covered by large plates dorsally, except dorsal-fin base.Ventral surface largely unplated from snout to anal fin or urogenital opening, larger specimens with few patches of odontodes close to pectoral fin insertion.Twenty-five perforated median plates, 24 lateral plates; four to five short oblong plates on caudal-fin base.All plates strongly sculpted with lines of odontodes more developed posteriorly.Numerous hypertrophied odontodes on evertible cheek plates, well developed in larger specimens.Ventral border of opercle with series of strong but short odontodes.Dorsal fin II,7; spinelet present and locking mechanism functional.Dorsal fin long and low, reaching adipose spine when adpressed.Dorsal-fin posterior membrane covering next three to four plates, but not reaching preadipose plate.Adipose fin large with posterior membrane well developed.Only one plate separating dorsal fin from preadipose plate.Caudal fin i,14,i, emarginate.Pectoral fin I,6, large, reaching well beyond posterior end of pelvic-fin base when adpressed.Pectoral fin covered by large odontodes in males.Pelvic fin i,5 reaching posterior end of anal fin base when adpressed.Anal fin i,4.All simple first rays covered by numerous short odontodes on their free surface.
Teeth long and deeply cuspidate.Cusps largely asymmetrical; internal cusp larger.Premaxilar and dentary bones of similar size and disposed parallel to anterior snout border.Maximum of 91 teeth on premaxillary and 96 on dentary.Modal number of premaxillary teeth 30; dentary teeth mode 34 (range of number of mandibulary teeth in Table 1).Buccal papilla short and digitiform.
Color in life.Body dark brown to olive at dorsum and sides, paler ventrally.Very faint pale spots over body, hardly visible on fins.Juveniles with whitish orange band on distal fourth of caudal and dorsal fins, narrower in adults (Fig. 6).
Color in alcohol.Similar to pattern of living specimens but opaque brown to dark olive ground color and almost indistinguishable pale marks.Bands on fins creamy (Fig. 5).
Distribution.Known from rio Xingu, in the area called Volta Grande do rio Xingu, immediately above Belo Monte falls and below Belo Monte village, and from rio Curuá, rio Iriri, the larger tributary of rio Xingu (Figs. 3 and 4b).Etymology.From the Greek chryso, meaning orange or yellow and loma meaning border, in allusion to the colored band at the border of the dorsal and caudal fins.A noun in apposition.
Popular name.This species is commonly known in the Brazilian aquarium trade as "aba laranja", (orange border), "cascudo Magnum", (large pleco), or L047.In English, this fish receives the name of mango pleco.
Ecological notes.Baryancistrus chrysolomus seems to be much rarer than B. xanthellus in the rapid stretches of "Volta Grande" of the rio Xingu (Fig. 4b).Differently from the preceding species, young specimens of B. xanthellus occur in marginal areas of the rapids, near the river banks, usually just one or two individuals.The individuals were found under rocks in places with slow to moderate flowing water, usually with sediment accumulation over the rocks and river bottom.Other loricariid species found in the same habitat were Peckoltia vittata and young individuals of Hypostomus spp.Adult B. chrysolomus were collected under large flat rocks settled directly on the river bottom, in places with considerable amounts of fine sediments.The diet of B. chrysolomus (only two specimens analyzed) is very similar to that described for B. xanthellus and was composed by loose algae (mainly diatoms) and occasional invertebrate larvae associated with fine sediments and sand grains.The combination of the type of food items detected, the presence of fine sediments in the gut, a very long (up to 20 times the body length) and coiled intestine, and tooth number and arrangement, also suggest a periphyton-combing feeding strategy for this species.

Discussion
Baryancistrus species are very conservative in shape, color pattern and overall measurements.All measurements and proportions of B. xanthellus and B. chrysolomus are largely similar; however, some features might be useful in the differentiation of all these taxa.Baryancistrus beggini seems to be a very small Baryancistrus species, reaching up to  and B. longipinnis.The type of B. longipinnis is largely plain, but it was described as having body, rays, and connecting membranes covered with small white spots, less conspicuous on rays and body (Kindle, 1895).Even B. chrysolomus has a faint spotted pattern, despite its striking clear band on dorsal and caudal fins.The only exception seems to be B. beggini with a plain dark coloration.Among the spotted Baryancistrus species, all dots along body and fins of the same individual are of similar sizes, except in B. demantoides and B. longipinnis.Baryancistrus demantoides have smaller dots on head and B. longipinnis have conspicuously minute dots on fin membranes, in contrast to larger dots on head, body and fin rays (Fig. 7).
Despite all morphological variation among different populations along the rio Xingu, the dotted-color pattern is quite pervasive.Recently, B. xanthellus was successfully breed in aquarium (Leuenberger, 2007) and the hatches have the color pattern cited above.
Baryancistrus catfishes are rapids-dwelling fishes found exclusively in fast-flowing waters over rocky bottom.Adult specimens generally occupy wide spaces between or under large rocks and boulders, whereas juveniles are mostly found under flat rocks at the bottom of shallow rapids.Specimens of several Baryancistrus examined so far have shown that these fishes are peryphyton grazers that feed on loosely attached algae associated to fine detritus (Zuanon, 1999).The new Baryancistrus species herein described comprise only two of several other undescribed forms already collected in the high-energy rivers that drain the Central Brazilian and Guiana plateaus.In the Brazilian Amazon, the ecological conditions that allow the occurrence of Baryancistrus species are found only in the peripheral portions of the basin, away from the lowlands.The downstream rapids present in most of the rio Amazonas tributaries that delimit the distribution range of Baryancistrus species are also targeted for the construction of large hydroelectric power plants in Brazil (Junk & Nunes de Mello, 1987).The large-scale habitat modifications that result from river damming represent the biggest threat to the conservation of rheophilic fishes, many of which still undescribed.Conservation efforts directed to the maintenance of pristine river stretches large enough to contain several rapids sections should be aimed, in order to allow the existence of viable populations of the remarkable diversity of fishes present in these aquatic habitats.

Fig. 4 .
Fig. 4. Rio Xingu: (a) Cachoeira Buraco do Inferno, type locality of Baryancistrus xanthellus, and specimen hidden in crevice in detail and (b) Furo do Ramiro, type locality of B. chrysolomus, and specimen hidden in crevice in detail (underwater photos Henrique Anatole).
Baryancistrus chrysolomus can be distinguished from all its congeners, except B. xanthellus, by the presence of a broad orange to yellow band along the entire distal border of dorsal and caudal fin (vs.all fins without yellow bands).Baryancistrus chrysolomus differs from B. niveatus and B. demantoides by the absence of clear dots on the body (vs.presence of clear dots on whole body in B. niveatus and in anterior part of the body in B. mm SL, 1 c&s, 58.4 mm SL, (1 not measured), Furo da Crente, 03º27'30"S 51º54'41"W, 17 Sep 1997, J. Zuanon.INPA 31408, 4,  55.6-92.2mmSL, Comunidade do Maia, 03º30'44"S 51º44'43"W, 9 Nov 2008, L. Rapp Py-Daniel & R. R. Oliveira.INPA 31438, 9, 47.4-89.1 mm SL, 1 c&s, 74.4 mm SL, (3 not measured), Comunidade do Maia, 03º31'42"S 51º45'02"W, 9 Nov 2008, L. Rapp Py-Daniel & R. R. Oliveira.INPA 31800, 3, 53.5 mm SL (2 not measured), Coqueiro, 03º06'54"S 51º43'15"W, 5 Nov 2008, L. Diagnosis.demantoides).Baryancistrus chrysolomus can also be distinguished from B. longipinnis, B. demantoides and B. niveatus by having a naked abdomen (vs.partially or completely plated in these three species).Baryancistrus chrysolomus can be further distinguished from B. beggini by the larger number of mandibulary teeth (around 70) (vs.34-36 in premaxillary and 34 in dentary in B. beggini).Baryancistrus chrysolomus differs from B. xanthellus by the general body color; in B. chrysolomus the body is dark with very faint, almost indistinguishable light marks, vs. a conspicuously spotted coloration in B. xanthellus.Both young of B. xanthellus and B. chrysolomus have wide light bands on dorsal and caudal fins, but only B. chrysolomus retains the band in adults.Besides, both species can be distinguished by the difference on the rest of the body coloration (spotted in B. xanthellus vs. almost plain in B. chrysolomus).
80 mm SL, in contrast to B. niveatus, B. longipinnis, B. xanthellus, and B. chrysolomus that can reach more than 200 mm SL.Dorsal-fin membrane is developed in all Baryancistrus species but it reaches the preadipose plate only in B. beggini and in young specimens of B. xanthellus and B. chrysolomus.Abdomen is partially to almost completely plated in large specimens of Baryancistrus niveatus, B. longipinnis, and B. demantoides, with concentration of plates on gular area, pectoral girdle, and around anus.In B. niveatus from the rio Tocantins, patches of odontodes were observed in all specimens larger than 96 mm SL.Besides, large specimens of B. niveatus show dense concentration of plates even below lower lip.Large specimens of B. longipinnis, also from rio Tocantins, despite showing concentration of plates in certain ventral areas (pectoral girdle, sides, around pelvics, and urogenital opening), do not have plates below the lower lip or on the gular area.The largest specimen of Baryancistrus beggini reached 80 mm SL and the species is cited as having a naked abdomen.All specimens of B. chrysolomus and B. xanthellus have the abdomen largely unplated, with larger specimens showing scattered patches of odontodes of few minute plates at pectoral-fin insertion or close to urogenital opening.Baryancistrus chrysolomus seems to have the largest mandibles, carrying up to 90 mandibulary teeth.Baryancistrus xanthellus has around 70, B. demantoides around 50 and B. beggini have 34-36 mandibulary teeth.Low tooth counts in B. beggini might be related to the small size of the fish, since small specimens of B. chrysolomus and B. xanthellus also have similar counts to B. beggini.Finally, the spotted color pattern seems to be most generalized.Baryancistrus niveatus, B. xanthellus, B. longipinnis, and B. demantoides (although partially) have white to yellowish white dots over a darker background.According to Werneke et al. (2005), Baryancistrus demantoides may have spots on basal portions of membranes and sometimes fins, different from B. niveatus, B. xanthellus, mm SL, Itupiranga, Capueranga, 05º10'29.8"S49º21'54"W.Baryancistrus niveatus: Syntypes: MNHN A.9453, 1, 245.5 mm SL, province of Goyaz, río Araguay.MNHN A.9454, 1, 231.9 mm SL, province of Goyaz, río Araguay.Non-types: Pará, rio Tocantins: INPA 2988, 18, 40.1-179.8mm SL, 1 c&s, 66.3 mm SL, pools on river bed below dam.