A new species of Panaqolus (Siluriformes: Loricariidae) from the rio Madeira basin with remarkable intraspecific color variation Author Cramer, Christian Andreas Author Py-Daniel, Lúcia Helena Rapp text Neotropical Ichthyology 2015 Neotrop. Ichthyol. 2015-08-25 13 3 461 470 http://dx.doi.org/10.1590/1982-0224-20140099 journal article 10.1590/1982-0224-20140099 2ab49e31-d925-463d-891e-f7061492af8b 1982-0224 4551377 12677D4B-E956-4303-AAB0-47C50106A099 Panaqolus nix , new species u r n:l s i d:z o o b a n k.o r g:a c t: 42F632 D 8-A127- 4 0 9 2 -B0 9B - 708882C0C3B9 ( Figs. 1-5 ) Panaque sp. 1: photo - Zawadzki & Chamon, 2013: p. 312. Panaque sp. 2: UFRO-I 6384, Zawadzki & Chamon, 2013: p. 313 Fig. 1. Dorsal, lateral, and ventral views of Panaqolus nix , holotype, INPA 39606, male, 110.1 mm SL, Brazil, Rondônia, rio Madeira, cofferdam at construction site of Santo Antônio hydroelectric power plant (former Santo Antônio rapids) (Photos by B. S. F. Barros). (see remarks for further explanation). Holotype . INPA 39606 , male, 110.1 mm SL, Brazil , Rondônia , rio Madeira , cofferdam at construction site of Santo Antônio hydroelectric power plant (former Santo Antônio rapids), 08°48’06”S 63°57’00”W , 14 Feb 2012 , C. A. Cramer. Paratypes . 48 specimens . Brazil : Rondônia State : INPA 39605 , 3 , 54.6-73.7 mm SL, Mamoré , near the São Lourenço community, trawl net fishing , 11°43’24.10”S 65°11’31.70”W , 30 May 2010 , L. H. Rapp Py-Daniel. INPA 41148 , 2 , 95.3 and 96.8 mm SL, rio Karipunas near mouth , 09°11’46.6”S 64°37’20.7”W , 4 Oct 2010 , NaturaeEnvironmentalCompany technicians. INPA 41149 , 1 , 85.0 mm SL, rio Madeira , near mouth of rio Karipunas , 09°12’18.9”S 64°37’08.4”W , 30 Oct 2010 , Naturae Environmental Company technicians. INPA 41150 , 28 , 32.8-112.2 mm SL, rio Madeira , cofferdam at the construction site of Jirau hydroelectric power plant (former Jirau rapids) , 09°15’15.7”S 64°38’50.4”W , 11-13 Nov 2011 , Naturae Environmental Company technicians. MZUSP 114009 , 3 , 68.5-76.2 mm SL; UFRO-I 6384 , 5 , 50.8- 80.7 mm SL, same data as INPA 39605. UFRO-I 7968 , 1 , 81.4 mm SL, rio Madeira , near Ilha do Búfalo , trawl net fishing , 09°08’51.10”S 64°32’33.70”W , 23 Oct 2010 , A. Ribeiro. UFRO-I 9974 , 1 , 53.6 mm SL, rio Madeira , below Santo Antônio rapids, trawl net fishing , 08°46’36.11”S 63°55’26.09”W , 23 Jul 2011 , L. Nogueira. UFRO-I 10050 , 1 , 90.4 mm SL, same data as INPA 39605. UFRO-I 13039 , 1 , 49.5 mm SL, same locality as holotype , 1 Dec 2011 , C. A. Cramer. UFRO-I 13040 , 1 , 57.7 mm SL, same data as UFRO-I 13039. UFRO-I 19646 , 1 , female, 97.3 mm SL, same data as holotype . Non-types. 1 specimen . Peru : ROM 92440 , 1 , 117.0 mm SL, Río Tambopata , Madre de Dios drainage, approximately 12°48’S 69°17’W , 16 Aug 2010 , K. Roach and A. Jackson . Diagnosis. The presence of small white dots on the whole body and fins distinguish Panaqolus nix from all congeners except P. albomaculatus . These dots are frequently faded in preserved specimens (typically, at least the dorsal and caudal fins show some traces of dots). Panaqolus nix can be distinguished from P. albomaculatus by having more dots on the trunk (on nearly all plates having one dot each vs. one dot each on less than half of the plates), a longer head-eye length (35.1-41.5% HL [mean 37.8] vs. 31.9-37.2% HL [mean 34.4]), a smaller orbital diameter (12.5-16.8% HL [mean 14.3] vs. 16.0-19.9% HL [mean 17.7]), and longer rictal barbels (9.7-19.6% HL [mean 13.8] vs. 1.6-8.9% HL [mean 4.9]). Only two other Panaqolus species ( P. dentex and P. koko ) lack alternating dark and light bands on fins. Panaqolus nix can be distinguished from P. dentex by lacking lighter colored saddles ( vs. three lighter colored saddles between dorsal-fin origin and caudal fin), by having a shorter head-pectoral length (22.4-28.2% SL [mean 25.5] vs. 27.2-38.1% SL [mean 29.2]), a lower caudal peduncle depth (9.3-11.4% SL [mean 10.5] vs. 11.0-13.3% SL [mean 12.2]), a smaller orbital diameter (12.5-16.8% HL [mean 14.3] vs. 16.4-22.8% HL [mean 17.8]), and a larger adult body size (more than 100 mm SL vs. less than 80 mm SL). Panaqolus nix differs from P. koko in the shape of the main tooth cusp (round and without or with very small lateral cusp vs. quadrangular and with strong lateral cusp), a smaller orbital diameter (12.5-16.8% HL vs. 18.9-20.8% HL [n=7]), and a larger interorbital width (34.3-39.3% HL vs. 29.4- 33.2% HL). Panaqolus albivermis typically has alternating light bands and rows of light dots or short lines on its body. Panaqolus nix can be separated from this species by having a shorter dorsal spine (26.2-32.5% SL vs. 33.0-36.0% SL [n=4]), a shallower caudal peduncle (9.3-11.4% SL vs. 12.2- 14.9% SL [n=4]), and a higher adipose-anal depth (17.9- 22.2% SL vs. 15.8-17.9% SL [n=4]). Panaqolus changae , P. gnomus , P. maccus , P. nocturnus , and P. purusiensis have alternating dark and light bands on the body (except P. nocturnus and adult P. purusiensis ) and fins ( vs. never showing bands on body or fins in P. nix ). Further, P. nix can be distinguished from P. changae by a narrower ventral cleithral width (29.0-33.8% SL [mean 31.0] vs. 33.4-37.4 [mean 34.8), a shorter head-pectoral length (22.4-28.2% SL [mean 25.5] vs. 28.0-31.1% SL [mean 29.9), a smaller orbital diameter (12.5-16.8% HL [mean 14.3] vs. 16.2-20.9% HL [mean 18.2]), and a larger adult body size (more than 100 mm SL vs. less than 90 mm SL). Panaqolus nix differs from P. gnomus by a lower dorsal-pectoral depth (26.9- 30.3% SL [mean 28.6] vs. 30.3-36.8% SL [mean 32.9]), a smaller interorbital width (34.4-39.3% HL vs. 39.7-44.7% HL), and a larger adult body size (more than 100 mm SL vs. less than 80 mm SL). Panaqolus nix can be separated from P. maccus by a shorter predorsal length (40.1-44.5% SL [mean 42.3] vs. 44.3-49.2% SL [mean 46.0), a shorter headpectoral length (22.4-28.2% SL [mean 25.5] vs. 27.2-44.1% SL [mean 30.8]), and a larger adult body size (more than 100 mm SL vs. less than 90 mm SL). Panaqolus nix can be distinguished from P. nocturnus by the angle of dentary tooth rows (less than 50° to nearly parallel vs. approximately 70°). Panaqolus nix differs from P. purusiensis by having a lower dorsal-pectoral depth (26.9-30.3% SL [mean 28.6] vs. 29.8-32.9% SL [mean 30.9;]), a lower caudal peduncle depth (9.3-11.4% SL [mean 10.6] vs. 10.9-14.0% SL [mean 12.1]), and a smaller mouth width (34.4-46.4% HL [mean 39.9] vs. 41.6-50.3% HL [mean 44.1]). Description. Counts and proportional measurements in Table 1 . Medium-sized loricariid with standard length of measured specimens up to 112.2 mm SL. Dorsal profile of head and snout strongly convex from snout tip to posterior tip of supraoccipital, straight and posteroventrally slanted between dorsal-fin origin and adipose-fin origin, gently concave through caudal peduncle to posterior tip of procurrent caudal-fin ray. Dorsal orbit margin only slightly raised, forming gentle ridge, narrowing anteriorly, from anterior orbit margin to area lateral to nares. Dorsal surface of trunk transversely flattened from dorsal-fin origin to adipose-fin base. Ventral profile of head and body flat from oral disk to anal-fin origin. Caudal peduncle oval in crosssection. Greatest body depth at dorsal-fin origin. Pectoralfin origin just posterior to orbit; pelvic-fin origin at vertical through origin of second dorsal-fin ray; anal-fin origin slightly posterior to vertical through origin of last dorsal- fin ray. Adipose fin with well-ossified leading spine bearing odontodes. Head and body covered by odontodes of uniform size and distribution. Enlarged odontodes on anterodorsal border of pectoral-fin spine. Cheek odontodes hypertrophied with anteriorly curved hooks on the tips; longest odontode extending to posterior cleithrum margin. Interorbital space flat or slightly convex. Eye dorsolaterally placed; orbit diameter 12.5-16.8% HL. Iris operculum present. Nares small and ovoid, slightly longer than wide. Table 1. Selected morphometrics of Panaqolus nix . Values are given as percents of standard length or head length. SD = standard deviation, n = number of specimens, H = holotype . Interlandmarks (ILM) are the two points between which measurements were taken (from Luj an et al ., 2010).

ILM	Measurement	H	n	range	mean±SD
1-20	Standard length (mm)	110.1	47	32.84-112.2	82.44
Percents of Standard Length
1-10	Predorsal length	43.1	47	40.1-44.5	42.3±1.0
1-7	Head length	35.7	47	33.2-39.3	35.2±1.3
8-9	Cleithral width	31.5	47	30.8-34.3	32.3±0.9
8'-9'	Cleithral width ventral	29.5	47	29.0-33.8	31.0±1.2
1-12	Head-pectoral length	27.0	47	22.4-28.2	25.5±1.3
12-13	Thorax length	25.3	47	22.7-30.7	26.4±2.0
12-29	Pectoral-spine length	31.1	46	29.5-34.9	32.0±1.4
13-14	Abdominal length	23.8	47	20.5-24.3	22.4±0.9
13-30	Pelvic-spine length	27.8	46	25.7-31.2	28.1±1.1
13-13'	Pelvic girdle width	20.2	47	19.4-22.7	20.9±0.7
14-15	Postanal length	34.8	47	31.7-37.6	34.9±1.3
14-31	Anal-fin spine length	18.3	46	12.8-18.3	15.3±1.2
10-12	Dorsal-pectoral depth	29.7	47	26.9-30.3	28.6±1.0
10-11	Dorsal-spine length	27.5	39	26.2-32.5	29.5±1.5
10-16	Dorsal-fin base length	27.5	47	20.5-28.8	25.3±1.3
16-17	Dorsal-adipose distance	17.7	46	13.7-19.4	17.2±1.2
17-18	Adipose-spine length	5.7	47	5.7-10.0	8.2±0.7
17-19	Adipose-upper caudal distance	12.0	47	12.0-20.7	15.8±1.4
15-19	Caudal peduncle depth	10.8	47	9.3-11.4	10.6±0.4
20-32	Caudal peduncle-middle caudal ray	23.5	42	9.5-26.0	17.7±4.1
20-33	Caudal peduncle-dorsal caudal spine	47.0	17	33.7-81.7	51.8±13.0
15-17	Adipose-lower caudal depth	20.5	47	20.5-25.2	22.6±1.1
Percents of Head Length
5-7	Head-eye length	35.6	47	35.2-41.5	37.8±1.3
4-5	Orbit diameter	13.5	47	12.5-16.8	14.3±1.0
1-4	Snout length	61.0	47	49.7-63.7	59.5±2.2
2-3	Internares width	11.8	47	10.5-14.7	12.2±0.9
5-6	Interorbital width	51.8	46	46.5-54.6	49.6±1.6
5'-6'	Dorsal interorbital width	35.0	47	34.4-39.3	36.7±1.2
7-12	Head depth	70.3	47	61.7-75.4	69.3±2.2
1-24	Mouth length	46.2	46	36.2-50.5	42.7±3.7
21-22	Mouth width	42.0	46	34.4-46.4	39.9±3.2
22-23	Barbel length	13.6	46	9.7-19.6	13.8±2.5

Oral disk round, maxillary barbels of moderate length (10-20% HL). Lips papillate; small patch of elongate fleshy papillae behind each dentary tooth row ( Fig. 2 ). Border of lips smooth, without papillae. Teeth spoon-shaped and unicuspidate or with very small lateral cusp. Premaxillary teeth 3-7 per ramus (mode 4), mandibular teeth 4-7 per ramus (mode 5). Premaxillary tooth rows angled at approximately 90°, dentary tooth rows acutely angled at approximately 50° or nearly parallel ( Fig. 2 ). small plates. Body with pronounced lateral ridge extending from cleithrum to posterior margin of fifth or sixth plate of the inframedian plate row, decreasing in prominence posteriorly. Trunk without elevated ridges. 7-8 plates on dorsal-fin base (mode 7), 5-7 plates between dorsal and adipose fin (mode 6), usually 1 azygous preadipose plate, 6-8 plates between adipose and caudal fin (mode 7), 2 plates on anal-fin base, 11-12 scutes between anal and caudal fin (mode 11), and 24-25 lateral plates (mode 25). Dorsal fin II,7-8 ( holotype II,7), pectoral fin I,6, pelvic fin i,5, anal fin i,4, caudal fin i,13-14,i ( holotype i,14,i). Spinelet triangular, dorsal-fin spine lock functional, posterior fin margin straight, margin of last two rays rounded. Dorsalfin origin closer to vertical line passing through pelvicfin origin than to vertical line passing through pectoralfin origin; not reaching adipose fin when adpressed. Last dorsal-fin ray without prolonged membrane. Adipose fin triangular; adipose-fin spine slanted posteroventrally, tip straight to curved ventrally, pointed; posterior margin of adipose-fin membrane concave to nearly vertical. Pectoralfin spine robust, membrane between spine and first ray without fleshy extension, distal fin margin straight. Pectoral fin, when depressed reaching 1/3 of pelvic fin. Pelvic-fin spine robust, distal margin slightly rounded, when adpressed reaching mid-length of anal fin. Caudal fin strongly forked; caudal-fin spines usually tipped with filaments of the length of the longest branched caudal-fin rays. Color in alcohol. Coloration of head, body and fins without bands or saddles. Base coloration varying from uniformly yellowish-white over light brown to dark brown or nearly black in different specimens. Small white dots (about 1/3 of the eye diameter) present on whole body and all fins; approximately one dot per plate; dots smaller on head. Dots faded to absent in preserved specimens, especially on trunk, but usually visible on fins. Caudal fin showing distinct dots or diffuse lighter markings. Fig. 2. Details of the mouth of Panaqolus nix : the dentary tooth rows are in an acute angle (below) or even nearly parallel (above) (MZUSP 114009, 68.8 mm + 76.2 mm SL). Scale bar = 5 mm. Head and body plated dorsally, except for small naked area around dorsal-fin base; some specimens with naked area at tip of snout. Supraoccipital bordered posteriorly by 2-3 (mode 3) plates on each side. Abdomen of adults ranging from incompletely plated (plates only in pectoral girdle, along sides, and posterior to pelvic fin) to nearly completely covered by small irregularly arranged platelets, with a small naked area around pelvic-fin origin and the urogenital orifice. Abdomen of juveniles of 70 mm SL or less naked or with only very few plates on the border with inframedian plates. Large naked area dorsally to pelvic-fin base, below ventral margin of inframedian plate row; sometimes showing 1-3 Color in life. Color of head, body and fins without bands or saddles. Base coloration varying from uniformly yellowishwhite over pale brown ( Fig. 3 ) to dark brown or nearly black in different specimens. In an aquarium, with clear water, light colored fish become dark in few days ( Fig. 4 ). Live specimens with small white dots (more or less 1/3 of the eye diameter) on whole body and all fins; approximately one dot per plate. Dots smaller on head. Caudal fin showing distinct dots or diffuse lighter markings. Sexual dimorphism. Mature males have longer odontodes on the pectoral-fin spine and on the caudal peduncle ( Fig. 5 ). The illustrated specimen was dissected and its gender was confirmed based on gonads examination. A large female (UFRO-I 19646) that was kept in an aquarium did not develop any conspicuously elongated odontodes over time. Some eggs were released during the process of preservation shortly after she died in captivity. Fig. 3. Variation in the color of Panaqolus nix : a) nearly white specimen (UFRO-I 10050, 90.4 mm SL) b), intermediately colored specimen (UFRO-I 7968, 81.4 mm SL) (Photos by B. S. F. Barros). Fig. 4. Live photo of the holotype of Panaqolus nix (INPA 39606; 110.1 mm SL). Distribution and Habitat. The known distribution of this species is the Madeira basin, including the Madeira, Mamoré, and Tambopata ( Madre de Dios drainage) rivers ( Fig. 6 ). Most of the specimens have been collected in cofferdams at the construction sites of the hydroelectric power plants of Santo Antônio and Jirau (former Santo Antônio and Jirau rapids), on the rio Madeira, by several technicians and ichthyologists hired by the two Consulting Environmental Companies responsible for the biological inventories in the area. Most of the remaining specimens have been caught in depths of 3.1 to 11 m (UFRO-I 6384, INPA 39605, MZUSP 114009) and 4.1 to 8.5 m (UFRO-I 6384) using trawl nets. This indicates that this species prefers deep-water habitats with strong current, which might help to explain its relative rarity in scientific collections. Etymology. From the Latin nix meaning snow, alluding to the color: in dark individuals the dots look like falling snowflakes, while pale individuals look like they have the whole body covered by snow; treated as a noun in apposition. Fig. 5 . Sexual dimorphic male of Panaqolus nix (INPA 41150 (#29859); 105.1 mm SL) with elongated odontodes on pectoral spine, caudal peduncle and caudal fin. Fig. 6. Distribution of Panaqolus nix . Open symbol: type locality. Symbols may represent more than one locality or lot. Ji = former Jirau rapids, SA = former Santo Antônio rapids. Remarks. ROM 92440 is not being considered in the type material as it is a dried specimen that disintegrated into several pieces. Zawadzki & Chamon (2013), in their list of Hypostominae of the rio Madeira, illustrated Panaque sp. 1 in page 312, and cited the lot UFRO-I 6384 as Panaque sp. 2, in page 315. In fact, there was a mistake in assigning the lots to the images. The illustration of Panaque sp. 1 shows in fact a specimen of Panaqolus nix and the correct number of this lot is UFRO-I 6384. The second illustration, Panaque sp. 2, is a different species and the correct numbers of the lots for this species are UFRO-I 6383 and UFRO-I 13109. So, Panaqolus nix was already known, but not named, as part of the ichthyofauna of the rio Madeira. Conservation status. The species seems to be widely distributed along rio Madeira, Mamoré and Tambopata as well. Despite the fact that part of its distribution includes two hydroelectric power dams, Jirau and Santo Antônio, the area of occurrence of Panaqolus nix goes well beyond the dams. Thus, considering that important threats to the species were not detected yet, P. nix should be classified as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014). In the last years parts of the known habitats have been severely altered by the construction of these hydroelectric power plants, destroying the former Santo Antônio and Jirau rapids and transforming more than 200 km of the rio Madeira, enlarging the riverbed and reducing the current. Additional collecting efforts should be conducted in that region in order to better understand the impacts of these constructions on the population of Panaqolus nix and to be able to adjust (if necessary) the evaluation of the conservation status of the species.