Rhinotocinclus isabelae, Reis & Lehmann, 2022

Reis, Roberto E. & Lehmann A., Pablo, 2022, A new genus of armored catfish (Siluriformes: Loricariidae) from the Greater Amazon, with a review of the species and description of five new species, Neotropical Ichthyology (e 220002) 20 (2), pp. 1-100 : 51-56

Rhinotocinclus isabelae , new species urn:lsid:zoobank.org:act:6A076A5D-9972-41D4-9BEE-036C45B7102F

( Figs. 29–30 ; Tab. 5 )

Holotype. MUSM 69737 , 17.6 mm SL, Río Nanay, between Puerto Almendra and Tarapoto , Iquitos, Loreto, Peru, 03°48’15”S 73°23’53”W, 5 Aug 2019, E. Mejia & Ornamental fishers .

Paratypes. Loreto, Peru: MUSM 69738 , 4, 14.6–17.2 mm SL (4 measured), MCP 54222 , 5, 14.1–17.3 mm SL (4 measured, 14.8–17.3 mm SL), collected with holotype . MCP 50154 , 4, 14.6–17.9 mm SL (3 measured, 17.0– 17.9 mm SL), aquarium shop , imported from Iquitos, obtained 12 Mar 2016, R. E. Reis. MCP 54755 , 2, 16.8–16.9 mm SL (2 measured) + 1 cs, MZUSP 125878 , 3, 15.4–17.6 mm SL, ROM 104102 , 16, 14.8–19.0 mm SL (1 measured, 17.9 mm SL) + 5 tissue vouchers + 1 cs, Río Tigre near community of Intuto, estimated 03°29’34.3”S 74°46’13.9”W, Jan 2018, Ornamental fishers for Oliver Lucanus (most fixed in ethanol).

Diagnosis. Rhinotocinclus isabelae is distinguished from R. acuen , R. bockmanni , R. chromodontus , R. dani , R. dinizae , R. hera , R. jumaorum , R. pentakelis , R. loxochelis n. sp., and R. marginalis n. sp. by possessing an adipose fin (vs. adipose fin absent), and by having a Y-shaped light mark from the snout tip to each nostril (Figs. 6A,B; vs. light mark V-shaped or present as two separate lines from snout tip diverging to each nostril). It is distinguished from R. collinsae , R. halbolthi , and R. hardmanni by lacking accessory teeth on both premaxilla and dentary (Figs. 5B,C; vs. accessory teeth present, Fig. 5A); the odontodes on the ventral surface of first pelvic-fin ray bent and pointing mesially (Fig. 9A; vs. odontodes aligned with main ray axis, Fig. 9B); a triangular dark spot on the anterior portion of the dorsal-fin membrane (Fig. 8C; vs. dorsal-fin spot absent); a Y-shaped light mark from snout tip to nostrils (vs. Y-shaped light mark absent); and a larger orbit, 29.4–34.3% snout length (vs. orbit 18.9–24.6% snout length). Rhinotocinclus isabelae is distinguished from the remaining congeners with an adipose fin, except R. variola , by having the dorsal-fin dark spot occupying more than half of the fin (Fig. 8C); and except for R. pilosus , by having 1–2 lateral abdominal plates (vs. 3–6 plates). It is further distinguished from R. variola by lacking dark dots smaller than a pupil diameter broadly distributed dorsally and ventrally on body (vs. dots present), and by having 21–29 premaxillary teeth (vs. 33–51 teeth); and from R. pilosus by having the abdomen fully plated (vs. abdomen mostly naked), and by the deeper caudal peduncle (8.1–8.8% vs. 6.3–7.5% SL). Rhinotocinclus isabelae is further distinguished from all congeners by its small body size (maximum standard length 17.9 mm).

Description. Proportional measurements in Tab. 5 . Dorsal profile of head straight to slightly concave from snout tip to area between nares, convex from that point to parieto-supraoccipital tip; straight to slightly convex from that point to origin of dorsal fin. Supraoccipital tip wih enlarged odontodes and slightly elevated. Dorsal profile of body mostly straight and descending from dorsal-fin origin to insertion of caudal fin. Trunk horizontally ovoid to roundly triangular and caudal peduncle vertically ovoid in cross section, vaguely flattened ventrally and compressed caudally. Body progressively narrowing posteriorly from cleithrum, more so behind dorsal fin.

Head widely flat between orbits; dorsal margin of orbit slightly elevated. Snout elongated, depressed, its anterior margin rounded in dorsal view, with small depression anterior to naris. Eye comparatively large, positioned dorsolaterally, with small to medium dorsal iris operculum. Posterior tip of parieto-supraoccipital with two keels of enlarged odontodes, fading in larger specimens. Slightly enlarged odontodes on snout border, especially on rostral and postrostral plates and on lower surface of pectoral and pelvic spines; enlarged odontodes curved and posteriorly oriented. Odontodes on trunk, especially posterior to dorsal fin, somewhat aligned. Canal cheek plate bent and elongated posteroventrally, contacting cleithum. Lips rounded, narrow, covered with minute papillae; papillae slightly decreasing in size towards lip margin. Lip margin with uniformly distributed papillae forming delicate fringe. Maxillary barbel mostly adnate to lower lip with small free distal portion. Teeth slender and delicate, bifid. Larger, medial cusp blade-like and slightly rounded, not elongated. Smaller, lateral cusp minute and pointed. Premaxillary teeth 21–29 (22); dentary teeth 18–24 (20); accessory teeth absent.

Body entirely covered by dermal plates except for ventral surface of head around lips, area around pelvic-fin insertion, and area around anus. Lateral plates arranged in five longitudinal series on trunk. Dorsal plate series complete, beginning at origin of dorsal fin, with 19 plates; mid-dorsal series incomplete, with 6–7 plates; middle series complete, with two ossified tubes and 23–24 plates. Lateral line on middle plate series with two ossified tubes, 7–9 plates bearing canal, 1–3 unperforated plates, 9–11 plates with canal, and 1–3 terminal plates without canal. Mid-ventral series incomplete with 12–16 plates; series terminating below or slightly anterior to adipose fin. Ventral series complete and continuous from pelvic-fin origin to caudal-fin base, with 18–20 plates. Predorsal plates forming two transverse rows anterior to nuchal plate. Preadipose azygous plates 1. Coracoid completely exposed ventrally, much longer than cleithrum; cleithrum exposed laterally with medial area and arrector fossa covered by skin. Lateral abdominal plates 1–3 (2/2). Middle abdominal plates arranged in 1–2 series, usually leaving unplated spaces between them and lateral abdominal plates. One or two preanal plates, usually anteriorly bordered by two plates. First anal-fin pterygiophore exposed in front of anal-fin as small, plate-like bone supporting odontodes. Total vertebrae 27, in two dissected specimens.

Dorsal-fin rays I,7; spine arched. Dorsal-fin origin slightly posterior to vertical through pelvic-fin origin. Dorsal-fin spinelet present, plate-like, roundly triangular dorsally and V-shaped anteriorly. Spinelet articulated to first dorsal-fin pterygiophore and dorsal-fin spine locking mechanism functional. Adipose fin present and well developed. Pectoral-fin rays I,6. Large spine slightly arched; tip of adpressed spine reaching distal third of pelvic fin. Pectoral-fin axillary slit present, with large slanted opening ventral to tip of posterior process of cleithrum. Pelvic-fin rays i,5, unbranbched ray shorter than branched rays, especially in females; fin short, with tip of adpressed fin almost reaching or reaching to anal-fin origin. Adult males with low fleshy flap along posterodorsal margin of thickened first pelvic-fin ray. Odontodes on ventral surface of thickened first pelvic-fin ray bent and oriented mesially. Anal-fin rays i,5. Caudal-fin rays i,14,i, with lower unbranched ray slightly longer than, or equal to upper.

Color in alcohol. Dorsal portions of head and trunk yellowish cream, cream to pale yellow ventrally. Dorsal and lateral surface of snout and cheeks mostly dark brown, sometimes with clear bar from nostril to ventral margin of snot. Light Y-shaped mark from snout tip diverging towards nostrils. Compound pterotic and most of parietosupraoccipial behind eyes dark brown. Posterior tip of parieto-supraoccipital and predorsal region yellowish cream and not forming inverted Y-shaped mark. Trunk with four conspicuous dark brown bars; bars 1 and 2 coalesced in wider bar; bars 4 and 5 very close or coalesced. Bars extending transversely from dorsal midline and narrowing ventrally, ventral tip of bar 2–4 reaching to ventral midline. Ventral surface mostly pigmented. Patches of dark chromatophores scattered on ventral head, especially on cheeks, dorsal surface of upper and lower lips, and gular region behind lower lip; branchiostegal membrane reddish brown. Tooth cusps reddish brown. Abdomen with heavy sparkling of dark chromatophores, caudal peduncle with dark brown pigmentation from lateral bars. Fins with transverse, conspicuous brown bands formed by concentration of chromatophores on rays and membrane. Dorsal fin with large dark triangular spot on anterior portion; spine with anterior third dark or reddish brown, soft rays with anterior 2/3 dark brown. Pectoral-fin spine with 4–5 dark brown spots, branched rays with dark brown and reddish brown pigmentation forming 2 irregular dark bands. Pelvic fin with one irregular dark band as continuation of dark bar 1. Anal fin with anterior half to 2/3 dark brown as continuation of dark bars 2 and 3. Adipose fin with one dark spot on preadipose aziguous plate and on middle portion of spine; these marks sometimes united. Caudal fin with reddish brown transverse blotch at base – bar 5, and cospicuous reddish brown band on posterior third; heavier on lobe tips.

Sexual dimorphism. Males have a small urogenital papilla immediately behind the anus and a low skin fold along the first, unbranched pelvic-fin ray, both characteristics being absent in females. Males also have slightly longer pelvic-fin unbranched ray which is almost as long as first branched ray than females. Males also possess larger nostrils and a more elevated lateral proifile of snout than females.

Geographical distribution. Rhinotocinclus isabelae is known from two localities near Iquitos, Loreto, Peru, one in the nearby Río Nanay and other in the Río Tigre ( Fig. 15 ).

Etymology. Rhinotocinclus isabelae is named in honor to Isabela Alho dos Reis, younger daughter of the senior author. Isabela is an enthusiast of biodiversity conservation and interested in aquarium fishes since she was very young. A patronym.

Conservation status. Rhinotocinclus isabelae is endemic to Peru and is currently known from two localities, the Río Nanay near Iquitos and the Río Tigre, a tributary to the Río Marañon. As only two localities are known the Extension of Occurrence (EOO) can not be estimated. Despite the species is apparently common, based on the high number of specimens exported by the aquarium trade, the impact of this activity is not understood and R. isabelae is preliminarily categorized as Data Deficient (DD) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019).

Remarks. This species is heavily harvested for the aquarium trade in Loreto, Peru, having been exported for many years. It is common in aquarium shops in Europe and easily found in aquarium webshops, where it is commercialized as Parotocinclus sp. “ Peru ” or Bumble Bee Otocinclus .

Figures

FIGURE 15 | Geographical distribution of Rhinotocinclus species of the R. britskii group in central and northwestern South America. Rhinotocinclus britskii (white dots); R. discolor n. sp. (purple dots); R. eppleyi (orange dots); R. isabelae n. sp. (pink dots); R. kwarup (red dots); R. longirostris (blue dots); R. pilosus n. sp. (yellow dots); R. polyochrus (cyan dot); R. variola (black dots); R. yaka (light green dots). T = Type-locality; T1 = type-locality of Parotocinclus britskii, T2 = type-locality of P. amazonensis, T3 = type-locality of P. aripuanensis.

FIGURE 29 | Rhinotocinclus isabelae, holotype, MUSM 69737, 17.6 mm SL, female, Río Nanay, between Puerto Almendra and Tarapoto, Iquitos, Loreto, Peru.

FIGURE 30 | Live specimen of Rhinotocinclus isabelae photographed in aquarium. Photo by Daniel Konn-Vetterlein.