Diapoma potamohadros, Ito & Carvalho & Pavanelli & Vanegas-Ríos & Malabarba, 2022

Ito, Priscila Madoka M., Carvalho, Tiago P., Pavanelli, Carla S., Vanegas-Ríos, James A. & Malabarba, Luiz R., 2022, Phylogenetic relationships and description of two new species of Diapoma (Characidae: Stevardiinae) from the La Plata River basin, Neotropical Ichthyology (e 210115) 20 (1), pp. 1-30 : 13-19

Diapoma potamohadros , new species

urn:lsid:zoobank.org:act:2BD1065C-94DD-4CFA-80C8-273FAF8DB491

( Figs. 5–7 ; Tab. 2 )

Bryconamericus sp. 2. — Russo et al., 2004:176–179 (diet analysis; tab. 2 fig. 2B, photo from NUP 719; fig. 4B1, head in lateral view; fig. 4B2, premaxillary teeth arrangement in ventral view; Salto Caxias Reservoir, Capitão Leônidas Marques, Paraná, Brazil).

Bryconamericus sp. C. — Baumgartner et al., 2006: 2 (checklist, Reservatório Salto Osório, Quedas do Iguaçu, Paraná, Brazil; referred as the same species listed by Russo et al., 2004).

Cyanocharax aff. alburnus. —Baumgartner et al., 2012:96 (description, table with measurements and counts, photo of vouchers NUP 2461 and NUP 4123, Reservatório Caxias, Capitão Leônidas Marques, Quedas do Iguaçu, Paraná, Brazil). — Delariva et al., 2013: 894–899 (diet; tabs. 1–5, NUP 6620 and NUP 7248, Reservatório Caxias, Capitão Leônidas Marques, Quedas do Iguaçu, Paraná, Brazil).

Cyanocharax sp. Iguaçu. — Thomaz et al., 2015:16 (phylogenetic relationships; voucher UFRGS 27622).

Diapoma aff. alburnus. — Deprá et al., 2018:20 (listed in comparative material; voucher NUP 11174).

Diapoma sp. — Mezzaroba et al., 2021: 6 (listed for Iguaçu River, NUP 6620, same voucher used in Delariva et al., 2013).

Holotype. UFRGS 28700, male, 48.6 mm SL, Iguaçu River , Salto Osório Reservoir , Quedas do Iguaçú municipality, Paraná State , Brazil, 25 °30’49”S 53°00’04”W, 17 Sep 2005, GERPEL (Grupo de Pesquisas em Recursos Pesqueiros e Limnologia) .

Paratypes. All from the Iguaçu River basin. Argentina , Misiones Province : MACN-ict 10364, 7, 31.3–41.7 mm SL (2 males, 37.5–37.9 mm, 5 females, 31.3– 41.7 mm SL), Iguazu Falls National Park , above Iguazu falls , Ñandú Chico stream, near 25°43’16.9”S 54°25’37.3”W, 16 Oct 1975. MLP 11343, 1 female, 43.5 mm SL, Deseado stream, 25º40’15.3”S 53º56’1.8”W, 29 Apr 2010, J. Casciotta & A. Almirón. Brazil, Paraná State: MCP 41353, 13, 44.1–56.4 mm SL (6 males, 46.9–51.4 mm SL, 7 females, 44.1–56.4 mm SL), 2 c&s, 1 male, 51.4 mm SL, 1 female, 50.7 mm SL, collected with holotype. MCP 41541, 53, 39.5–52.0 mm SL (30 males, 39.5–50.7 mm SL, 23 females, 42.2–52.0 mm SL), Salto Osório Reservoir, Quedas do Iguaçú municipality, 25°30’49”S 53°00’04”W, Mar 2007, GERPEL. MCP 41542, 56, 37.2–53.0 mm SL (24 males, 39.5–49.0 mm SL, 32 females, 37.2–53.0 mm SL), Salto Osório Reservoir, Quedas do Iguaçú municipality, 25°30’49”S 53°00’04”W, Nov 2005, GERPEL. NUP 22687, 9, 40.8–53.4 mm SL, Quedas do Iguaçu municipality, Salto Osório Reservoir, 25°32’05”S 52°59’09”W, 1 Nov 2006, GERPEL. UFRGS 27622, 27, 37.5–53.2 mm SL, TEC 1827 (23 males, 37.5–53.0 mm SL, 4 females, 43.6–53.2 SL), Salto Osório Reservoir, Quedas do Iguaçu municipality, 25°32’05”S 53°00’33”W, 21 Nov 2010, C. S. Pavanelli .

Non-types. All from Brazil, Paraná State, Iguaçu River basin. NUP 7245, 259, 14.0–60.0 mm SL, Três Barras do Paraná municipality, Adelaide River , 25°27’18”S 53°18’26”W, 1 Aug 2009, Nupelia. Capitão Leônidas Marques municipality, Salto Caxias Reservoir: NUP 719, 52, 44.4–56.5 mm SL, 25°32’12”S 53°29’11”W, 13 Aug 1997, Nupelia. NUP 2461, 76, 28.3–71.2 mm SL, 25°32’12”S 53°29’11”W, 18 Jan 2000, Nupelia. NUP 6620, 11, 52.0–61.0 mm SL, 25°32’12”S 53°29’11”W, 1 Aug 2005, Nupelia. NUP 7247, 24, 54.0–60.0 mm SL, 25°32’12”S 53°29’11”W, 1 Jul 2000, Nupelia. NUP 7248, 16, 55.0–62.0 mm SL, 25°32’12”S 53°29’11”W, 1 Sep 2000, Nupelia. Quedas do Iguaçu municipality, Salto Osório Reservoir: NUP 4123, 75, 20.7–41.0 mm SL, 25°30’49”S 53°00’04”W, 17 Sep 2005, Gerpel. NUP 4129, 1, 27.0 mm SL, 25°30’49”S 53°00’04”W, 17 Sep 2005, GERPEL. NUP 4335, 23, 26.5– 33.2 mm SL, 23°30’48”S 53°00’04”W, 1 Feb 2005, GERPEL. NUP 4336, 6, 42.2–53.9 mm SL, 23°30’48”S 53°00’04”W, 1 Dec 2004, GERPEL. NUP 6229, 57, 24.5–56.4 mm SL, 25°30’49”S 53°00’04”W, 27 Jan 2008, GERPEL. NUP 11161, 8, 53.1–53.9 mm SL, 25°32’05”S 52°59’09”W, 1 Nov 2006, GERPEL. NUP 11162, 7, 50.3–55.1 mm SL, 25°32’05”S 52°59’09”W, 1 Jul 2007, GERPEL. NUP 11163, 7, 46.6–55.8 mm SL, 25°32’05”S 52°59’09”W, 15 Jan 2007, GERPEL. NUP 11164, 13, 46.2–57.1 mm SL, 25°32’05”S 52°59’09”W, 1 May 2007, GERPEL. NUP 11169, 1, 51.1 mm SL, 25°32’05”S 52°59’09”W, 1 Jul 2008, GERPEL. NUP 11174, 44, 48.6–57.0 mm SL, 25°32’05”S 52°59’09”W, 1 Jul 2008, GERPEL .

Diagnosis. Diapoma potamohadros can be distinguished from D. alburnum , D. dicropotamicus , and D. itaimbe by having discontinuous perforation of lateral line scales (vs. complete lateral line); and can be also distinguished from these species, except from D. alburnum , by having an unpigmented adipose fin (vs. darkly pigmented adipose fin in D. dicropotamicus and D. itaimbe ). Diapoma potamohadros can be distinguished from D. pyrrhopteryx , D. speculiferum , D. terofali , and D. thauma by the absence of modified scales in the caudal fin (vs. presence); and can be distinguished from D. pyrrhopteryx and D. speculiferum by the lack of a posterior elongation of opercular bones (vs. opercle and subopercle posteriorly extended). Diapoma potamohadros can be distinguished by the distal border of the anal fin concave in males (vs. convex in males of D. alegretense , D. tipiaia , and D. uruguayense , and nearly straight in males of D. guarani , D. lepiclastum , and D. obi ); by the lower number of scales forming the anal-fin sheath (5–12 vs. 12–18 in D. alegretense , 13–20 in D. lepiclastum , and 20–28 in D. uruguayense ); and by the number of branched anal-fin rays (20–26 vs. 29–35 in D. uruguayense ). Diapoma potamohadros can be distinguished from D. nandi and D. obi by a lower body depth (27.6–31.9% SL vs. 32.4–38.8% SL in D. nandi ; 35.5–44.1% SL in D. obi ). The new species is distinguished from D. tipiaia and D. pampeana by the presence of five or more cusps on the teeth in the inner series of premaxilla (vs. tricuspid teeth). Diapoma potamohadros can be further distinguished from D. alegretense and D. uruguayense by having a longitudinal black stripe extending posteriorly on the middle caudal-fin rays (vs. black stripe on middle caudal-fin rays absent); and from D. guarani by absence of a conspicuous black blotch on the caudal-fin base (vs. presence).

Description. Morphometric data are given in Tab. 2 . Largest specimen 56.4 mm SL. Body laterally compressed, maximum depth at vertical through dorsal-fin origin or at posterior tip of pelvic-fin rays when adnate to body. Dorsal head profile slightly convex or straight, dorsal body profile slightly convex from tip of supraoccipital spine to dorsal-fin origin, straight from this point to adipose-fin origin. Dorsal profile of caudal peduncle somewhat straight to slightly concave. Ventral body profile convex from tip of lower jaw to pelvic-fin origin, straight between pelvic and anal-fin origins, straight or slightly convex from this point to caudal peduncle. Ventral profile of caudal peduncle straight to slightly concave. Head with anterior region rounded. Anterior and posterior nostrils rounded, separated by skin fold from anterior nostril; posterior nostril opening larger, with double size than anterior nostril.

Mouth terminal or slightly superior, anterior tip of premaxilla slit at horizontal through 1/3 depth of eye. Premaxilla with two rows of teeth ( Fig. 6 ). Outer row with two (1), three (9), four* (18), or five (7) tricuspid teeth. Inner row with four (16) or five* (19) teeth; usually penta- to hexacuspid (rarely heptacuspid), with centralmost cuspid slightly larger than others. Maxilla with two (7), three* (10), four (14), five (3), or six (1) teeth ( Fig. 6 ); usually tricuspid (30) and rarely penta- or hexacuspid (4). Posterior tip of maxilla reaching vertical through anterior margin of eye. Dentary with six (3), seven* (9), eight (8), nine (5), 10 (6), 11 (1), or 12 (3) teeth; four anterior-most teeth large and pentacuspid, followed by conical, bi- or tricuspid teeth ( Fig. 6 ). Second anteriormost tooth slightly displaced ventrally in comparison with contiguous, similar sized teeth of dentary. First gill arch with six (11), seven* (14), or eight (9) gill rakers on epibranchial, 10 (1), 11 (9), 12* (16), or 13 (8) on ceratobranchial.

Dorsal-fin rays ii, eight* (35). Nine pterygiophores in dorsal fin (2 c&s). Dorsal-fin origin at vertical slightly anterior to anal-fin origin, often reaching posterior tip of pelvic-fin rays. Adipose-fin origin at vertical crossing posteriormost two to three anal-fin rays. Anal-fin rays iii (9), iv* (19), or v (7), 20 (1), 21 (1) 22 (8), 23 (11), 24* (10), 25 (3), or 26 (1). Twenty-seven pterygiophores in anal fin (2 c&s). Anal-fin origin at posterior half of body, usually posterior to vertical through dorsal-fin origin. Pectoral-fin rays i (35), eight (1), nine* (13), 10 (15), or 11 (6). Pectoral fin inserted immediately after the opercle, posterior tip at vertical surpassing pelvic-fin origin, usually reaching the half of elongated scale covering pelvic-fin origin. Pelvic-fin rays i,6* (35). Pelvic-fin origin at vertical between 9th or 12th scale of lateral line. Caudal fin forked with 10/9 principal rays (2 c&s).

Scales cycloid, almost all with the same size and form, except for anal-fin base with elongated scales. Most of specimens (28) with discontinuous lateral line, with tubed scales interspersed by non-tubed scales; five specimens with incomplete lateral line with canal of lateral line present until 11 to 19th scales, and two specimens with lateral line scales completely tubed. Absence of lateral-line canal on caudal-fin interradial membrane. Total number of scales in longitudinal series 35 (2), 37 (7), 38* (11), 39 (12), 40 (2), or 41 (1). Predorsal scales 12 (8), 13* (15), 14 (11), or 16 (1). Five (8) or six* (27) scale rows between dorsal-fin origin and row of lateral line. Three (5), four (5), or five* (24) scale rows between lateral line and pelvic-fin origin. Circumpeduncular scales 14* (20) or 15 (14). One row of scales forming sheath along anal-fin base with five (1), six (3), seven (4), eight (8), nine* (7), 10 (6), or 12 (1) scales. Scales along anal-fin base cover at least to 11th anal-fin branched ray. Caudal-fin lower lobe covered by a set of four or five large unmodified scales, not extending beyond anterior one-third of caudal-fin rays. Total number of vertebrae 36, 16 precaudal and 20 caudal (2 c&s).

Coloration in alcohol. Ground color pale or yellowish in preserved specimens. Black chromatophores delineating scale margins on latero-dorsal portion of body, forming a feeble chevron pattern on the lateral of body above anal-fin base. Black chromatophores concentrated along mid-dorsal region of head and anterior tip of snout and lower jaw. Infraorbitals and opercle bright silver. Black humeral blotch vertically elongated. Black and large midlateral stripe, more diffuse anteriorly near humeral blotch, wide and conspicuous from vertical through dorsal fin to caudal peduncle, extending posteriorly to proximal portion of middle caudal-fin rays. Caudal fin with scattered black chromatophores along dorsal, ventral, and posterior portion. Dorsal fin with diffuse black chromatophores on

interradial membranes. Adipose fin hyaline with few scattered black chromatophores. Anal fin dusky, with scattered black chromatophores on interradial membranes; distal region more darkly pigmented. First unbranched pectoral-fin ray pigmented with black chromatophores, other rays hyaline. Pelvic fin hyaline.

Sexual dimorphism. The presence of bony hooks was only observed in two adult males from the Ñandú Chico stream ( Fig. 7A ; MACN-ict 10364, male, 37.8 mm SL). The distal border of the anal fin is concave in both males and females, lacking the sexual dimorphism observed in other species of the genus (see Diagnosis). All pelvicfin rays of males (except the last one) have several pairs (usually one pair per segment) of short slender hooks extended mainly on the segmented region of each ray but also present on the unsegmented area of the middle rays. The pelvic-fin hooks are oriented anterolaterally on the inner border of each ray and its branches. The distal half of the anal-fin rays of males bears extremely tiny hooks that are arranged in one pair per each segment from the last unbranched ray until the 9th branched ray and are oriented nearly anteriorly or laterally on the posterior border of the rays. Gill glands were found in approximately the six to 10 anteriormost filaments of the lower branch of the

first branchial arch. The gill glands were not observed on females and in all unsexed examined specimens up to 25 mm SL.

Geographical distribution. Diapoma potamohadros is known from the lower Iguaçu River basin, a tributary to the Paraná River, downstream from the Salto Santiago Reservoir to the Iguaçu falls ( Fig. 4 ) .

Ecological notes. According to a previous study (Russo et al., 2004, tab. 3), this new species of Diapoma consumes mainly allochthonous resources, such as adults of Diptera (60% in April, flood period), macrophytes (79.4% in August, flood period), Hymenoptera (70.2% in September 54.8% in November and 58.8% in December) and adult Ephemeroptera (67.5% in May and 44.3% in October).

Etymology. We named the species Diapoma potamohadros in reference of Iguaçu River (Gr.: potamo = river; hadros = big, bigger), a noun in apposition of “Iguaçu” (“igua” = river, “açu” = big in tupi-guarani, Brazilian indigenous language).

Conservation status. The specimens were collected in a restricted area that is under influence of the reservoirs of Salto Osório, Salto Caxias and some tributaries upstream the Iguazu falls within the Iguazu Falls National Park in Argentina. Based on collecting sites, we estimate the EOO to be 5,197.778 km ² and AOO to be 343.000 km ², which

can be classified as Vulnerable (VU) with criteria B(B1: EOO <20.000 km ², B2: AOO <2.000 km ²). However, no specific threats were detected for the entire distribution of this species, and its population seems to be abundance in the nature, based in total of specimens collected and registered in the scientific collections. Therefore, this species can be classified as Least Concern ( LC) according to IUCN categories and criteria ( IUCN Standards and Petitions Subcommittee, 2019).

Figures

FIGURE 4 | Map of part of southern Brazil, Paraguay, Uruguay, and east Argentina showing the geographic distributions of Diapoma pampeana (white squares) and D. potamohadros (paratypes with pink circles, and non-types with plus sign in red). Stars indicate type localities.

FIGURE 5 | Holotype of Diapoma potamohadros, UFRGS 28700, male, 48.6 mm SL, Brazil, Paraná, Quedas do Iguaçu, Salto Osório Reservoir.

FIGURE 6 | Right premaxilla, maxilla and dentary of Diapoma potamohadros, UFRGS 41353, 51.4 mm SL, paratype.

FIGURE 7 | Anal fin of Diapoma potamohadros, MACN-ict 10364, A. Male, 37.8 mm SL; B. Female, 37.6 mm SL. Lateral view, left side. Scale bars = 1 mm.

Tables

TABLE 2 | Morphometric data for holotype and 34 paratypes of Diapoma potamohadros.

	Holotype		Males (N = 18)		Females and juveniles (N = 16)
		Range	Mean	SD	Range	Mean	SD
Standard Length (mm)	48.6	37.5–52.9	47.9		31.3–56.4	45.7	–
Percentages of standard length
Head length	22.7	20.4–22.9	21.3	1.8	20.3–24.6	22.6	2.3
Depth at dorsal-fin origin	29.1	28.6–31.9	29.8	0.9	27.6–30.7	29.0	1.0
Snout to dorsal-fin origin	52.0	51.0–55.9	52.6	1.4	50.8–57.01	54.1	2.0
Snout to pectoral-fin origin	23.8	21.7–27.5	23.4	1.4	22.1–27.8	24.4	1.8
Snout to pelvic-fin origin	45.1	43.2–46.2	44.6	0.9	42.7–47.8	42.4	1.5
Snout to anal-fin origin	59.2	59.5–63.4	61.2	1.2	59.6–64.9	61.9	1.6
Distance between dorsal- and adipose-fin origins	38.4	32.6–39.3	36.8	1.8	31.0–38.3	35.7	2.1
Dorsal -fin origin to caudal-fin base	50.2	46.6–52.6	50.3	1.4	45.3–52.3	48.9	2.1
Dorsal-fin length	22.6	20.7–24.1	22.2	1.0	20.4–23.9	22.2	1.1
Dorsal-fin base length	11.8	10.2–12.5	11.5	0.6	8.9–12.0	11.1	0.9
Pectoral-fin length	22.1	20.0–21.9	20.9	0.6	20.5–22.5	21.4	0.6
Pelvic-fin length	14.1	12.5–14.9	13.6	0.6	12.6–14.6	13.7	0.6
Anal-fin base-length	30.3	28.1–31.4	29.5	0.9	26.5–32.4	29.2	1.6
Caudal peduncle depth	9.9	9.2–10.9	9.7	0.5	8.9–11.6	10.1	0.7
Caudal peduncle length	11.8	11.5–14.1	12.8	0.7	11.1–13.4	12.6	0.7
Percentages of head length
Snout length	20.8	19.7–26.8	22.0	1.8	19.0–26.9	22.6	2.3
Horizontal eye length	42.3	39.6–44.6	42.6	1.2	39.4–45.3	42.5	1.7
Postorbital head length	37.7	33.0–40.8	36.8	1.8	34.2–38.3	36.1	1.1
Least interorbital width	33.8	33.2–37.3	35.1	1.2	31.3–39.1	35.0	2.0
Upper jaw length	37,5	37.5–42.2	39.5	1.5	38.3–43.0	40.2	1.4
Dentary length	39.1	38.5–46.2	40.7	1.9	39.1–45.4	41.5	1.9