Rediscovery and redescription of the endangered Hypostomus subcarinatus Castelnau, 1855 (Siluriformes: Loricariidae) from the Rio São Francisco basin in Brazil

Hypostomus subcarinatus Castelnau, 1855 is rediscovered in the Lagoa da Pampulha, an urban lake in the Rio das Velhas basin (Rio São Francisco system) in the state of Minas Gerais, southeastern Brazil. Herein, H. subcarinatus is redescribed and diagnosed from its congeners based on characters such as blue-tan dorsal fin in live specimens, slender bicuspid teeth, dentaries angled more than 90 degrees, moderate keels along lateral series of plates, small roundish dark spots, one plate bordering supraoccipital, by having nuptial odontodes mainly on pectoral, dorsal and caudal-fin rays, and long anal-fin unbranched ray. The rediscovery of H. subcarinatus more than 160 years after its original description was an unexpected event, because the Lagoa da Pampulha is an artificial, silted and polluted urban lake. The lake is located in downtown Belo Horizonte, the third largest urban agglomeration in Brazil with a population exceeding 5.9 million inhabitants.


Introduction
The loricariid Hypostomus subcarinatus was described by Castelnau [1] from a vague type locality stated as "des rivière de la province des Mines" [streams from the state of Minas Gerais]. Therefore, it was hypothetically associated with Eastern Brazilian coastal drainages and to the Rio São Francisco basin [2]. However, despite some ichthyological survey efforts in these systems [3,4], no scientific record of H. subcarinatus was undoubtedly stated for more than 160 years. This historical lack of records of H. subcarinatus lead to some hypotheses, a) an erroneous locality designation in the original description by Castelnau; b) species rarity or endemicity to specific locations; c) several ongoing populational extinction processes; or d) imprecise identifications. PLOS  In 2014 a fish environmental monitoring survey was conducted in the Lagoa da Pampulha, an artificial silted and polluted urban lake of the Rio São Francisco basin system and located in downtown Belo Horizonte, Minas Gerais State, southeastern Brazil. Unexpectedly, seven large specimens of the catfish Hypostomus were captured. Subsequent examination did not allow to recognize them as any of the commonly found species of Hypostomus of the Rio São Francisco basin. However, in comparison to Hypostomus original descriptions, as well as to type series of Hypostomus from worldwide scientific fish collections the specimens were recognized as Castelnau's (1855) lost Hypostomus subcarinatus. In this work the species is redescribed and the importance of the conservation of urban water bodies is claimed.

Material and methods
Fishes were collected under permits from the Instituto Chico Mendes de Conservação da Biodiversidade-ICMBio n. 9101-1/2017. Captured individuals were anaesthetized and sacrificed by immersion in eugenol (active ingredient: phenolic eugenol, 4-Allyl-2-methoxyphenol-C10H12O2, derived from stems, flowers and leaves of Eugenia caryophyllata and Eugenia aromatica trees) [5], fixed in 10% formalin solution and later preserved in 70% ethanol. These procedures are in accordance to the 'Ethical Principles in Animal Research' guidelines adopted by the National Council of Control of Animal Experimentation (CONCEA). Measurements and counts of bilaterally symmetrical features were taken from the left side of the body, whenever possible. Measurements were taken using a digital caliper to the nearest 0.1 mm. Methodology and terminology of measurements follows Boeseman [6], modified by Weber [7] and Zawadzki et al. [8]. Plate counts and bone nomenclature follow Schaefer [9], modified by Oyakawa et al. [10]. Standard length (SL) is expressed in millimeters and all other measurements are expressed as percent of standard length or head length (HL), unless otherwise noted. Institutional abbreviations of material deposited follow Fricke & Eschmeyer [11], except ICT-UFMG (Coleção Ictiológica do Centro de Coleções Taxonômicas do Instituto de Ciências Biológicas da Universidade Federal de Minas Gerais). The species conservation status was assessed through the criteria of the International Union for Conservation of Nature (IUCN standards and petitions subcommittees, 2017 [12]) guidelines.

Hypostomus subcarinatus Castelnau, 1855
Diagnosis. Hypostomus subcarinatus is distinguished from all congeners by having a bluetan dorsal fin in living specimens (vs. not having a blue-tan dorsal fin). Additionally, H. subcarinatus is diagnosed from the species of the H. cochliodon group by having slender viliform bicuspid teeth (vs. robust spoon-shaped teeth) and by having dentaries angled to each other more than 90 degrees (vs. dentaries angled from 80 to 90 degrees); from the remaining conge- ; from the species above by having a more slender and elongate body, what can be somewhat depicted by the anal-fin unbranched ray length longer than head depth (vs. anal-fin unbranched ray length shorter than head depth).
Description. Morphometric data in Table 1. Overall view of body in Figs 1, 2 and 3. Head moderately depressed and slightly compressed. Snout and anterior profile of head slightly pointed in dorsal view. Eye of small size, dorsolaterally positioned. Dorsal margin of orbit not raised. Greatest body width at cleithrum, narrowing from dorsal-fin region to caudal-fin origin. Dorsal profile of head convex from snout tip to vertical through interorbital region, forming angle of about 40˚with ventral region of head; slightly convex from that point to dorsal-fin origin; straight from that point to caudal-peduncle end; rising to procurrent rays of dorsal fin. Ventral profile almost straight from snout tip to insertion of pelvic-fin unbranched ray; tapering slightly, straight from pelvic-fin insertion to first ventral caudal-fin procurrent ray. Anterior portion of caudal peduncle rounded with its dorsal surface compressed; posterior portion ellipsoid. Mesethmoid forming weak longitudinal bulge from snout tip to nares. Supraoccipital bone with slightly-developed median ridge and short posterior process bordered by single plate. Weak bulge originating lateral to nares, passing through supraorbital, and extending as ridge along dorsal portion of compound-pterotic. Opercle large, its horizontal length equal to distance between nares, with thin skin layer surrounding its ventral edges to subocular cheek plates. Oral disk round, moderate in size; its margins smooth. Lower lip falling short of transverse line through gill openings; ventral surface with two or three transverse dermal flaps posteriorly margining each dentary ramus; short naked area followed by larger area with numerous small papillae decreasing in size distally. Maxillary barbel moderately long, slightly larger than eye to nare distance; mostly free from lower lip. Odontodes present on anterior surface of upper lip, just below snout. Dentaries moderate to strongly angled, averaging from 90˚to 100˚between left and right dentary rami. Teeth viliform, bicuspid with lateral cusp smaller than mesial cusp; crown bent inward. Internally to mouth, transversal areas of short papillae bordering each premaxillary and dentary teeth rami. Median buccal papilla present and well developed. Body covered with five rows of dermal plates with moderately-developed odontodes, except on base of dorsal fin and small naked area on snout tip. Predorsal region with very slight median keel. Dorsal, mid-dorsal, mid-ventral, and ventral series of plates with moderate keels. Median series with weakly developed keels; bearing uninterrupted lateral line. Ventral series bent ventrally. Ventral surface of head covered with platelets, except for region behind lower lip. Abdomen covered with minute platelets in specimens larger than 110 mm SL, with  exception to very small areas around pectoral-and pelvic-fin insertions (ICT-UFMG 2885). Distal portion of first anal-fin pterygiophore exposed.
Dorsal fin II,7, its origin at vertical just posterior midpoint between pectoral-and pelvic-fin insertions; first spine present as V-shaped spinelet. Distal margin of dorsal fin slightly convex; tip of last dorsal-fin ray falling two or three plates short of adipose-fin spine. Adipose-fin spine compressed and slightly curved inward. Pectoral fin I,6, its distal border straight. Pectoral-fin spine slightly curved ventrally, covered with moderately developed odontodes. Odontodes curved inward, more developed along distal portions of spine, particularly in larger specimens; emerging from swollen papillae. Tip of adpressed pectoral fin reaching to basal one-fourth to one-fifth of adpressed pelvic-fin unbranched ray. Pelvic fin i,5, its distal border straight to slightly convex; its adpressed unbranched ray surpassing one to two plates beyond anal-fin origin. Anal fin i,4, its tip reaching to seventh plate after its origin; its distal margin straight. Caudal fin i,14,i, its margin falcate, with ventral lobe longer than dorsal.
Color in alcohol. Overall ground color of dorsal and ventral regions of body and fins grayish-brown (Figs 1 and 2). Head, trunk and fins covered by numerous small dark brown spots except on lower lip. Spots very small, numerous, close together and inconspicuous in head; increasing in diameter towards posterior region of body; spots more conspicuous on fins and dorsolateral regions of trunk. Spots on ventrolateral regions of trunk usually inconspicuous. Ventral surface of body usually with faded dark spots; conspicuousness variable among specimens. All fins with many small dark spots; spots irregularly distributed on spines and either on unbranched and branched rays. Some specimens with five faded oblique dark bars on dorsum, first bar on posterior portion of head, stronger at middle of orbit, second bar at first dorsal-fin branched rays, third bar at last dorsal-fin branched ray, fourth bar at anterior region of adipose fin and fifth bar at procurrent caudal-fin rays. Ventral surface of body slightly clearer than dorsal surface.
Color in life. Color pattern of living specimens similar to preserved ones, except for more brownish-green background, black and more conspicuous spots and dorsal fin with blue-tan (Fig 3).
Sexual dimorphism. No sexual dimorphism was observed. Distribution. Hypostomus subcarinatus is currently known from one locality (Figs 4 and 5), the Lagoa da Pampulha, an eutrophic reservoir, in the Rio das Velhas basin, city of Belo Horizonte. The description of Hypostomus subcarinatus by Castelnau [1] was based on only one specimen from the ambiguous type locality "des rivières de la province des Mines". However, Papavero [13] (p. 149-159) outlined the details of Castelnau's itinerary, illustrating it with a map (map 12). Castelnau [14] traveled through Minas Gerais by road from the mouth to the headwaters of the Rio Paraibuna, tributary of Rio Paraíba do Sul. Then, he crossed the Rio das Mortes (upper Rio Paraná basin) at Barbacena, and its tributary the Rio Carandaí. Then, he entered to the Rio São Francisco basin, crossing the headwaters of the Rio Paraopeba, and reached the Rio das Velhas (Rio São Francisco basin) at Santa Rita (currently municipally of Nova Lima) and followed the river downstream, crossing some of its tributaries to Sabará. In the narrative of his passage through Minas Gerais, Castelnau [1,14]  Thus, the presence of H. subcarinatus in the Lagoa da Pampulha as a result of an anthropic introduction from some unknown close or distant place seems highly improbable. The distance between this lake and the Rio das Velhas is less than 11 kilometers in a straight line. Castelnau [14], visited the village of Curral del Rei (currently, city of Belo Horizonte) and may have collected the holotype in the surroundings. It is probable that specimens of H. subcarinatus inhabit some other spots along the Rio das Velhas basin. However, until now, no specimens have been assigned to this species except for the unique holotype and those from the Lagoa da Pampulha.
Habitat and conservation status. Hypostomus subcarinatus has only been found in the Lagoa da Pampulha, a silted and polluted urban reservoir (Fig 5). The Lagoa da Pampulha was formed in 1938 to supply water to the city of Belo Horizonte. Since 1970, the reservoir has became quite eutrophic due to the dump of domestic and industrial effluents from the city, causing recurrent cyanobacteria blooms [15]. Friese et al. [16] found significant values of heavy metals in lake sediments. As Hypostomus are known to be detritivorous fishes they probably assimilate considerable proportions of those metals, as Veado et al. [17] found in the omnivorous Oreochromis niloticus in the Lagoa da Pampulha. Despite some ichthyologic survey efforts, H. subcarinatus were up to now not collected in the surroundings of the reservoir. Therefore, H. subcarinatus with an estimated Area of Occupancy (AOO) equal to the Lagoa da Pampulha area (1.96 km 2 ) is herein assessed as Critically Endangered (CR) according to IUCN criteria [12], becoming the first threatened species of the genus. Hypostomus subcarinatus occurs sympatrically to three alien cichlids in the lake, Coptodon rendalli, Oreochromis niloticus, Parachromis managuensis.

Discussion
Concerning external morphology, the most similar species to Hypostomus subcarinatus are the eastern Brazilian drainage dwellers H. affinis, H. interruptus, H. nigrolineatus, H. punctatus and H. scabriceps. All species have an elongate and narrow body with small to mediumsized dark spots and weak to moderate keels along lateral series of plates. Besides the bluetan dorsal-fin, H. subcarinatus is distinguished from these congeners by being more elongate and slender than the aforementioned species and by having a longer anal-fin unbranched ray. Anal-fin unbranched ray length is almost equal or equal to snout length vs. equal to the pre-nasal length (that, is the distance from the snout tip to the anterior margin of the naris). Additionally, H. subcarinatus is distinguished from H. nigrolineatus by having unorganized dark spots versus dark spots horizontally aligned to form conspicuous stripes on laterals of trunk. Regarding the species of Hypostomus from the Rio São Francisco basin, the most morphologically similar species is the recently described H. velhochico Zawadzki, Oyakawa & Britski, 2017 [18]. Hypostomus subcarinatus is mainly differentiated from H. velhochico by attaining a larger size, having odontodes on dorsal-fin spine and on unbranched caudal-fin rays, and by having more numerous and closer to each other dark spots on head, trunk and fins.
Few papers dealt with Hypostomus from the Rio São Francisco basin and its taxonomy is far from being well known [18]. Most Hypostomus records for the basin are from dam construction monitoring programs, and not results of ecological or taxonomic citations on scientific papers. However, several specimens of Hypostomus are deposited in ichthyological collections, mainly in the Museu de Ciências Naturais da PUC Minas (MCNIP), ICT-UFMG, Museu Nacional, Rio de Janeiro (MNRJ) and at the Museu de Zoologia, Universidade de São Paulo (MZUSP). Except for the specimens from the Lagoa da Pampulha, H. subcarinatus were not recognized from Hypostomus samples at these collections.
Finding H. subcarinatus in the Lagoa da Pampulha in downtown Belo Horizonte, the third largest metropolis of Brazil with more than 5.9 millions inhabitants, was indeed a quite unexpected event. This is a fish larger than 300 mm in total length rediscovered more than 160 years after its original description and last citation. The individuals were found in the shallow, polluted urban lake, which is a significant ecological event. Some papers address ecological surveys in urban neotropical streams [19,20], but focusing fish conservation on urban neotropical artificial lake is an underestimated issue. Present findings highlight the importance that taxonomy-focused scientific surveys in such highly vulnerable water bodies, which can reveal important data to vertebrate conservation purposes. Urban lakes are frequently dragged, canalized, dried, and cleaned, to a series of reasons for human purposes. This study shows that even bad smelling urban waters as the Lagoa da Pampulha can harbor rare and endangered fish, deserving conservation management.