Research Article |
Corresponding author: Wilson J. E. M. Costa ( wcosta@acd.ufrj.br ) Academic editor: Nicolas Hubert
© 2022 Wilson J. E. M. Costa, Axel M. Katz.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Costa WJEM, Katz AM (2022) A new catfish of the genus Trichomycterus from the Rio Paraíba do Sul Basin, south-eastern Brazil, a supposedly migrating species (Siluriformes, Trichomycteridae). Zoosystematics and Evolution 98(1): 13-21. https://doi.org/10.3897/zse.98.72392
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A new species of the catfish genus Trichomycterus is described from the Rio Paraíba do Sul, south-eastern Brazil. This species exhibits some morphological character states that are unique amongst congeners, including a robust opercle and a long interopercle with numerous odontodes (50–60 opercular and 90–100 interopercular), a black bar on the basal portion of the caudal fin and a dark brown flank with a well delimited dorsal yellow stripe. It also exhibits some morphological traits that are uncommon amongst congeners, such as the presence of nine pectoral-fin rays. The presence of a shallow hyomandibular outgrowth and a ventrally expanded pre-opercular ventral flap suggests that this species is closely related to T. melanopygius, T. pradensis and T. tete. The new species also differs from T. melanopygius, T. pradensis and T. tete by having an emarginate caudal fin and a single median supra-orbital pore S6. Anecdotal evidence suggests that T. largoperculatus and T. pradensis have migratory habits, a condition not previously reported for eastern South American trichomycterines.
Biodiversity, Brazilian Atlantic Forest, comparative osteology, fish migration, Neotropical Region, systematics
The Trichomycterinae, one of the eight subfamilies of the Neotropical catfish family Trichomycteridae, comprises a diversified group with most species inhabiting swift freshwater environments between southern Central America and southern South America (
Species of Trichomycterus from the Rio Paraíba do Sul and adjacent coastal basins have been studied and described since the nineteenth century (
This study focuses on a new species collected over 10 years ago in the main channel of the Rio Paraiba do Sul, noteworthy by exhibiting a distinctive colour pattern and some unique osteological features amongst eastern South American trichomycterines. Equally remarkable is the report of upstream migration during the collection, which is new for eastern South American trichomycterines. Due to the peculiar combination of morphological character states exhibited by the new species, making its phylogenetic positioning uncertain amongst trichomycterines, a formal description was not made before the conclusion of deeper phylogenetic studies on trichomycterines from eastern South America (
Morphometric and meristic data were taken following
UFRJ 6987, 77.8 mm SL; Brazil: Estado do Rio de Janeiro: Município de Além Paraíba: Rio Paraíba do Sul just below Ilha dos Pombos Dam, 21°50'36"S, 42°34'46"W, about 105 m a.s.l.; L. P. Bastos, 10 March 2009.
UFRJ 6988, 7, 35.2–91.5 mm SL; UFRJ 6989, 3 (C&S), 55.7–46.2 mm SL; CICCAA 02695, 2, 50.7–51.3 mm SL; all collected with holotype.
Trichomycterus largoperculatus is distinguished from all species of Trichomycterus s.s. by having more opercular odontodes (48–62 vs. 11–31), more interopercular odontodes (92–100 vs. 23–72) and a unique colour pattern consisting of a dark brown flank with a longitudinal pale yellow stripe on its dorsal portion (vs. never a similar colour pattern) and the presence of a black bar on the basal portion of the caudal fin (vs. absence).
Morphometric data are in Table
Holotype | Paratypes (n = 8) | |
---|---|---|
Standard length (mm) | 77.8 | 46.6–91.5 |
Percentage of standard length | ||
Body depth | 16.4 | 14.3–17.5 |
Caudal peduncle depth | 11.2 | 9.6–11.4 |
Body width | 9.2 | 9.6–14.7 |
Caudal peduncle width | 3.9 | 3.1–4.4 |
Pre-dorsal length | 60.4 | 58.0–62.9 |
Pre-pelvic length | 53.5 | 53.3–58.1 |
Dorsal-fin base length | 13.6 | 11.9–13.4 |
Anal-fin base length | 8.7 | 8.9–10.4 |
Caudal-fin length | 16.7 | 15.0–16.8 |
Pectoral-fin length | 15.5 | 13.8–17.0 |
Pelvic-fin length | 11.5 | 10.7–12.9 |
Head length | 21.9 | 21.9–25.1 |
Percentage of head length | ||
Head depth | 45.2 | 42.4–48.5 |
Head width | 81.8 | 73.9–83.6 |
Snout length | 48.4 | 42.1–45.9 |
Interorbital length | 24.3 | 21.6–28.3 |
Pre-orbital length | 15.8 | 13.2–16.4 |
Eye diameter | 11.7 | 12.2–16.1 |
Dorsal and anal fins subtriangular; total dorsal-fin rays 13 (iv + II + 7), total anal-fin rays 11 (iv + II + 5); anal-fin origin posterior to dorsal-fin base. Dorsal-fin origin at vertical through centrum of 16th or 17th vertebra; anal-fin origin at vertical between centrum of 22nd or 23rd vertebra. Pectoral fin subtriangular in dorsal view, posterior margin slightly convex, first pectoral-fin ray terminating in filament, its length about 20% of pectoral-fin length without filament; total pectoral-fin rays 9 (I + 8). Pelvic fin truncate, its posterior extremity reaching urogenital papilla; pelvic-fin bases medially separated by interspace about half-length pelvic-fin base; total pelvic-fin rays 5 (I + 4). Caudal fin emarginated, upper and lower corners rounded to slightly pointed; total principal caudal-fin rays 13 (I + 11 + I), total dorsal procurrent rays 18–22 (xvii–xxi + I), total ventral procurrent rays 14–16 (xiii–xv + I). Vertebrae 35 or 36. Ribs 11 or 12. Two dorsal hypural plates, corresponding to hypurals 4 + 5 and 3, respectively; single ventral hypural plate corresponding to hypurals 1 and 2 and parhypural.
Laterosensory system (Fig.
Mesethmoidal region and adjacent structures (Fig.
Jaw suspensorium and opercular apparatus (Fig.
Branchial arches (Fig.
Flank dark brown with longitudinal pale yellow stripe on dorsal portion, ventral portion yellowish white; in juveniles and most adult specimens (Fig.
Not recorded.
Trichomycterus largoperculatus is known only from the type locality, in the middle Rio Paraíba do Sul, south-eastern Brazil (Fig.
From the Latin, the name largoperculatus (with large opercle) refers to the broad opercular odontode patch resulted from the high number of odontodes (48–62) (Fig.
Osteological structures of Trichomycterus largoperculatus: A. Mesethmoidal region and adjacent structures, middle and left portion, dorsal view; B. Left jaw suspensorium and opercular apparatus, lateral view; C. Middle and left portion of brachial arches, ventral view of dorsal elements on left, dorsal view of ventral elements on right. Abbreviations: ac4, accessory cartilage basibranchial 4; b2–3, basibranchials 2–3; bc4, cartilaginous basibranchial 4; c1–5, ceratobranchials 1–5; e1–4, epibranchials 1–4; epf, expanded pre-opercular ventral flap; p3, pharyngobranchial 3; h1–3, hypobranchials 1–3; hog, hyomandibular outgrowth; pt4, pharyngobranchial 4 tooth-plate. Larger stippling represents cartilages.
Two conspicuous apomorphic conditions of the external morphology of T. largoperculatus include the presence of an emarginate caudal fin and nine pectoral-fin rays. Although these conditions may be present in different trichomycterine lineages, the occurrence of these morphological character states is uncommon amongst eastern South American trichomycterines. In the over 40 species included in the clade comprising Cambeva and Scleronema, which is sister to Trichomycterus s.s., the caudal fin is always truncate or subtruncate and there are eight rays or less in the pectoral fin, never nine (
Trichomycterus largoperculatus has a long maxilla that is conspicuously longer than the premaxilla (Fig.
Some morphological character states, here recorded as diagnostic for T. largoperculatus, are interpreted as autapomorphies. Firstly, in this species, the opercular and interopercular patches of odontodes are broad, with numerous odontodes. There are about 50–60 opercular and 90–100 interopercular odontodes, thus greatly surpassing the maximum of about 30 opercular and 70 interopercular odontodes in all other species of Trichomycterus s.s., as well as in all species of its sister group, the clade containing Cambeva and Scleronema. Secondly, no other trichomycterid has a flank colour pattern consisting of a dark brown flank crossed by a dorsal yellow stripe like that present in T. largoperculatus (Figs
The type series of T. largoperculatus was collected while fish were migrating upstream along the Rio Paraíba do Sul main channel (V. Abilhoa, pers. com.). Although migration for feeding, reproduction and spawning is a common feature amongst large species of Neotropical pimelodid catfishes (e.g.
The only exception amongst trichomycterines from eastern South America river basins was observed during field studies on February 2014, when hundreds of specimens of T. pradensis, about 20 mm of total length, were seen forming a continuous upstream flow in the lower Rio Jucuruçu (16°23'34"S, 39°17'09"W), eastern Brazil, just about 25 km from the sea (WJEMC, pers. obs.), thus contrasting with larger specimens, between about 40 and 110 mm SL that were only found in the upper section of the basin (
Special thanks are due to Vinicius Abilhoa for donating specimens of the new species for study. Thanks are also due to Donald Taphorn, Heok Hee Ng and Paulo Andreas Buckup for suggestions and criticisms. This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq; grant 304755/2020-6 to WJEMC) and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ; grant E-26/202.005/2020 to AMK and E-26/201.213/2021 to WJEMC). This study was also supported by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Finance Code 001) through Programa de Pós-Graduação em: Biodiversidade e Biologia Evolutiva /UFRJ; Genética/UFRJ; and Zoologia, Museu Nacional/UFRJ.