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81
Verh. Ges. Ichthyol. Bd. 4, 2004
Verhandlungen der Gesellschaft für Ichthyologie Band 4, 2004, 81-90
A new species of Otothyrini
(Siluriformes: Loricariidae:
Hypoptopomatinae) from the Río Uruguay basin,
Argentina
Eine neue Art des Stammes Otothyrini (Siluriformes: Loricariidae:
Hypoptopomatinae) aus dem System des Rio Uruguay, Argentinien
María de las Mercedes Azpelicueta1, Jorge Casciotta1,
Adriana Almirón1 and Stefan Körber2
1División Zoología Vertebrados, Museo de La Plata, Paseo del Bosque, 1900 La Plata,
Argentina, e-mail: azpeli@museo.fcnym.unlp.edu.ar
2Friesenstr. 11, D-45476 Mülheim, Germany, E-Mail: pecescriollos@aol.com
Summary: A new species of the tribe Otothyrini is described from the Río Uruguay basin in
Misiones, Argentina. Epactionotus aky n.sp. was collected in the streams Fortaleza and Garibaldi; both
streams are headwaters of the arroyo Yabotí-Guazú. The new species is diagnosed by the following
combination of characters: 1) 21 to 23 lateral plates; 2) light stripes extended from snout tip to
supraoccipital level; 3) caudal fin with dark vertical stripes; 4) ventral surface of body completely
covered by small platelets; 5) 1-4 feeble serrae on distal portion of pectoral spine posterior margin.
Key words: Argentina, río Uruguay basin, Hypoptopomatinae, Otothyrini, Epactionotus
Zusammenfassung: Aus dem System des Rio Uruguay in Misiones, Argentinien, wird eine neue Art
der Tribus Otothyrini beschrieben. Epactionotus aky n.sp. wurde in den Bächen Fortaleza und Garibal-
di, beide Quellgewässer des Arroyo Yabotí-Guazú, gesammelt. E. aky n.sp. wird durch die folgenden
Merkmale charakterisiert: 1) 21 bis 23 Platten entlang der Seitenlinien; 2) helle Linien von der
Schnauzenspitze bis zur Höhe des Supraoccipitals; 3) Schwanzflosse mit dunklen vertikalen Streifen;
4) Bauchseite vollständig mit kleinen Platten bedeckt; 5) Präsenz von 1-4 schwach ausgebildeten
sägeartigen Fortsetzen auf dem äußeren Teil des hinteren Randes des Pectoralstachels;
Schlüsselwörter: Argentinien, Río-Uruguay-System, Hypoptopomatinae, Otothyrini, Epactionotus
Resumen: Se describe una nueva especie de la tribu Otothyrini, de la cuenca del Río Uruguay en
Misiones, Argentina. Epactionotus aky n.sp. fue recolectado en los arroyos Fortaleza y Garibaldi,
ambos arroyos son nacientes del arroyo Yabotí-Guazú. La nueva especie se define por los siguientes
caracteres: 1) 21 a 23 placas laterales; 2) líneas claras extendidas desde el hocico hasta la altura del
supraoccipital; 3) aleta caudal con lineas oscuras verticales; 4) superficie ventral del cuerpo comple-
tamente cubierta por pequeñas placas; 5) presencia de 1 a 4 sierras débiles en el margen posterior,
porción distal, de la espina pectoral.
Palabras claves: Argentina, cuenca del Río Uruguay, Hypoptopomatinae, Otothyrini, Epactionotus
1. Introduction
Within the loricariids the subfamily Hypopto-
pomatinae includes two tribes, the Hypop-
topomatini and the Otothyrini (Schaefer 1991,
1998). Many changes have been done in the last
years in the systematic of the genera within both
tribes; at present, they are diagnosed phyloge-
82
netically. Ten genera were included in the tribe
Otothyrini (Reis and Schaefer 1998). Within this
tribe, Eurycheilichthys and Hisonotus are the only
genera found in the Río Uruguay basin, in Ar-
gentina (Aquino 1997), Brasil (Reis and Schae-
fer 1998), and Uruguay (Aquino et al. 2001).
The aim of this paper is to describe a new
remarkable green species of Epactionotus col-
lected in two streams of the Río Uruguay ba-
sin, in the province of Misiones, Argentina.
2. Material and methods
Specimens were cleared and stained (C&S) fol-
lowing Taylor and van Dyke (1985). Mea-
surements were taken as straight line distances
using digital callipers, following Reis and Schae-
fer (1992). Counts include the holotype and
ten paratypes (one specimen cleared and
stained). Numbers in brackets indicate the
quantity of specimens. Values of the holo-
type are indicated by an asterisk. Institutional
abbreviations are Asociación Ictiológica, La Pla-
ta, Argentina (AI); Muséum d’ histoire natu-
relle, Genève, Switzerland (MHNG).
Comparative material examined: Hisonotus ma-
culipinnis, AI 122, 1 ex., 27.5 mm SL (C&S),
Argentina, Corrientes province, Río Paraná, Ita
Ibaté; Hisonotus maculipinnis, AI 123, 5 ex., 23.4-
27.0 mm SL, Argentina, Corrientes province,
Río Paraná basin, Esteros del Iberá, Rincón
del Diablo, Laguna Yacaré; Hisonotus sp., AI
120, 1 ex., 23.3 mm SL, Argentina, Misiones,
Río Uruguay basin, arroyo Oveja Negra; Hypo-
ptopoma inexpectatum, AI 119, 1 ex., 35.0 mm
SL, Argentina, Corrientes province, Río Paraná,
Puerto Abra; Otocinclus flexilis, AI 117, 2 ex.,
36.0-36.5 mm SL, Argentina, Entre Ríos pro-
vince, Arroyo Ñancay; Otocinclus vestitus, AI 118,
3 ex., 26.0-30.4 mm SL, Argentina, Corrientes
province, Río Paraná, Puerto Abra; Otocinclus
vittatus, AI 121, 1 ex., 27.0 mm SL (C&S), Ar-
gentina, Corrientes province, Río Paraná, Ita
Ibaté; AI 127, 1 ex., 26.2 mm SL, Argentina,
Buenos Aires province, Río de la Plata basin,
Arroyo El Pescado.
3. Results
Epactionotus aky n.sp. (Figs. 1, 2)
Holotype
AI 124, 30.5 mm SL, Argentina, Misiones, Río
Uruguay basin, Arroyo Garibaldi (26°38’46.1”
S – 53°59’55” W), coll. J. Casciotta, A. Almirón
and F. Ruiz Díaz, December 2002.
Paratypes
MHNG 2643.39, 2 ex. 32.2-32.6 mm SL, Ar-
gentina, Misiones, Río Uruguay basin, Arro-
yo Fortaleza at bridge of RP 21, from Paraíso
to Salto del Moconá, about 7 km down from
Paraíso, (26°45’57”S-54°10’56.5”W), coll. S.
Körber, J. O. Fernández Santos and R. Fili-
Fig. 1: Epactionotus aky, holotype, lateral view, 30.5 mm SL.
Fig. 1: Epactionotus aky, Holotypus, Seitenansicht, 30,5 mm SL.
83
Verh. Ges. Ichthyol. Bd. 4, 2004
Fig. 2: Epactionotus aky, holotype, dorsal view, 30.5 mm SL.
Fig. 2: Epactionotus aky, Holotypus, Aufsicht, 30,5 mm SL.
Tab. 1: Morphometric data of the holotype and 10 paratypes of Epactionotus aky n.sp. Standard
length (SL) is expressed in mm. HL: head length. SD: standard deviation.
Tab. 1: Morphometrische Daten des Holotyps und von zehn Paratypen von Epactionotus aky n. sp.
Die Standardlänge (SL) ist in mm angegeben. HL: Kopflänge. SD: Standardabweichung.
berto, 7. January 2001. AI 125, 8 ex., 25.0-35.0
mm SL, same collecting data as holotype.
3.1. Diagnosis
The new species is diagnosed by the follo-
wing combination of characters: 1) 21 to
23 lateral plates; 2) light stripes extended
from snout tip to supraoccipital level; 3)
caudal fin with dark vertical stripes; 4) ven-
tral surface of body completely covered by
small platelets; 5) 1-4 feeble serrae on distal
portion of pectoral spine posterior mar-
gin.
84
3.2. Description
Morphometrics of holotype and 10 paratypes
are presented in Table 1. Body elongated, head
not depressed. Greatest body depth at dorsal
fin origin. Head as wide as trunk. Dorsal pro-
file of head from snout tip to orbit level
straight; almost convex over supraoccipital.
Snout tip rounded in dorsal view, without
enlarged odontodes. Rostral median plates
with notch. A very small area anterior to nares
without plates. Eyes placed dorsolaterally,
horizontal eye diameter shorter than subor-
bital depth, and as large as nare diameter. Iris
diverticulum short. Three infraorbitals sur-
rounding orbit. Margins and surface of lips
covered with papillae. Maxillary barbels short.
Jaw teeth bifid, tooth slender with major cusp
oval or slightly truncate, expanded distally,
and a very minor cusp pointed or truncate.
Absence of accessory teeth on premaxilla and
dentary. One series of teeth, 12-17 (mode 15)
on premaxilla and 10-15 (mode 15) on den-
tary. Pterotic-supracleithrum showing very
large openings of swimbladder capsule. Pre-
opercular sensory canals directed toward pte-
rotic-supracleithrum.
Body covered by dermal plates except for naked
area around anus, lateral opening of swimblad-
der capsule, base of paired fins, and area between
pectoral girdle and lower lip. Lateral and anterior
rostral plates slightly reflected ventrally. Three or
four predorsal pairs of plates. Five lateral series
of plates on trunk (Fig. 3). Lateral plates 21-23;
21(1), 22(3*), 23(7). Plates bearing lateral-line
canal in two sectors, anterior one with 3-5; 3(1),
4(9*), 5(1), and posterior sector with 5-10; 5(1),
6(2*), 8(1), 9(4), 10(2), one specimen without
perforated plates on posterior portion. First two
trunk lateral line plates reduced to ossicles; pos-
terior portion of second ossicle and anterior
portion of third plate placed on rib of sixth
vertebra. Abdomen almost completely covered
by plates, variable in size and shape. Anal fin
preceded by 3 or 4 pairs of lateral plates, a wide
median plate between them separating two or
three posterior lateral plates. Coracoid and clei-
Fig. 3: Epactionotus aky, view of lateral plates of
trunk.
Fig. 3: Epactionotus aky, Ansicht der Platten auf
der Körperseite.
1 mm
thrum exposed ventrally, excluded arrector fos-
sae and area surrounding it.
Odontodes covering head, trunk, and fin rays.
Head and trunk odontodes uniformely dis-
tributed. Odontodes usually small on body,
except for somewhat enlarged odontodes on
ventral margin of snout, pectoral, pelvic, and
anal spines, and a tuft at posterior supraocci-
pital tip in some specimens, independently
from sex. Odontodes along anterior margin
of snout biserially arranged; dorsal and ven-
tral series not separated by a naked area.
Dorsal fin with one spine and seven branched
rays, its origin posterior to vertical through
pelvic-fin origin. Dorsal fin moved relatively
posterior to seventh vertebra. First dorsal-fin
proximal radial contacting eigth vertebra.
Adipose fin absent. Pectoral fin with one
spine and 6 branched rays, reaching half of
85
Verh. Ges. Ichthyol. Bd. 4, 2004
Fig. 4: Epactionotus aky, colour in life, lateral view.
Fig. 4: Epactionotus aky, Lebendfärbung, Seitenansicht.
pelvic-fin length. Pectoral spine with 1-4 feeble
serrae on distal tip of posterior pectoral
spine margin. Pelvic fin with one spine and
five branched rays, surpassing anal-fin origin
only in males. Caudal fin with fourteen bran-
ched rays. Presence of a large pectoral fin axil-
lary slit. Total vertebral number 29 (one C&S
specimen), including Weberian apparatus and
caudal complex centrum as one element. Neu-
ral spine of seventh vertebra not contacting
nuchal plate. Neural spine of seventh verteb-
ra narrow, without expansion.
3.3. Colour in life (Figs. 4-6)
Ground colour of dorsolateral surface of
body brilliant green, ventral surface of head
and trunk yellowish with small dark dots.
Two white stripes from tip of snout to the
eyes, continuing over eyes, and posteriorly
up to a vertical through posterior tip of su-
praoccipital. Both stripes ending in small
whitish dots. A light dot around supraocci-
pital tuft. A light area running on ventral
margin of snout, preopercle, opercle, and
partially on cleithrum. One series of small
dorsolateral dots placed from anterior area
of dorsal fin to level of middle anal fin;
those small dots whitish to yellowish. Dor-
sal and ventral whitish areas on caudal pe-
duncle; both areas extending on dorsalmost
and ventralmost caudal-fin rays. Green stripe
across middle caudal-fin rays. Paired fins
translucent, with white rays and small black
dots. Dorsal fin with greenish rays and black
dots.
3.4. Colour in alcohol
Ground colour of dorsolateral surface of
body brownish, ventral surface of head and
trunk pale brown. Two light stripes from
snout tip to the eyes, continuing posteriorly
reaching level of supraoccipital tip. Behind
the eyes, the stripes are narrower. Remains
of dorsal narrow light stripes extended
from dorsal fin origin to caudal peduncle.
Ventrolateral margin of snout and head
light brown. Posterior tip of supraoccipi-
tal with a triangular light area, usually bea-
ring enlarged odontodes. Pectoral, pelvic,
dorsal, and anal fins pale brown with dots
forming series of darker bands. Caudal fin
pale brown, with a dark irregular spot on
base and about two or three dark vertical
stripes.
86
Fig. 6: Epactionotus aky, colour in life, ventral view.
Fig. 6: Epactionotus aky, Lebendfärbung, Bauch-
ansicht.
3.5. Etymology
The specific epithet aky is a Guaraní word
meaning green.
3.6. Distribution
This species is known from the arroyos Gari-
baldi and Fortaleza. Both streams are head-
waters of the arroyo Yabotí-Guazú, which
flows into the Río Uruguay, in the argentinean
province of Misiones (Fig. 10).
3.7. Habitat
Arroyo Garibaldi (Fig. 7) is a stream about
4 m wide and 0.70 to 1.50 m deep, with
small falls and scarce submerged vegeta-
tion. The bottom had rocks and mud; the
water was turbid because of rainfall. Its
temperature in february was 20.6 °C, pH
6.7, dissolved oxygen 8.8 mg×l-1 and the
conductivity 36.6 µS×cm-1. The specimens
were collected with hand nets, in the mar-
Fig. 5: Epactionotus aky, colour in life, dorsolateral view
Fig. 5: Epactionotus aky, Lebendfärbung, seitliche Aufsicht.
87
Verh. Ges. Ichthyol. Bd. 4, 2004
gin of the stream near submerged vege-
tation.
Arroyo Fortaleza: The new species was only
caught downstream (Fig. 8) the bridge and it
was found in dense groups of Echinodorus sp.
This groups of plants formed green sub-
merged islands in the elsewhere sandy and
stony habitat. The individuals were not seen
by eye, but only seined out of the plants with
nets, as they were hanging on the trunks or
underneath the leaves. The depth of the stream
was variable, averaging about 0.50 m, with clear
and rapid flowing water. On January 7th, 2001,
the temperature at 10:00 am was 23.4 °C, pH
7.5, dissolved oxygen 12 mg×l-1 and conduc-
tivity 40 µS×cm-1. Arroyo Fortaleza is the type
locality of Bryconamericus uporas and Astyanax
paris and the habitat of the recently described
tetragonopterine Cyanocharax lepiclastus (Mala-
barba and Weitzman, 2003). These species were
found upstream and downstream the bridge;
the zone upstream the bridge presents a diffe-
rent kind of habitat, with no submerged vege-
tation, rocky buttom, and pools more than
2 m deep (Fig. 9).
Fig. 7: Arroyo Garibaldi, Misiones, Argentina,
type locality of Epactionotus aky.
Fig. 7: Arroyo Garibaldi, Misiones, Argentini-
en, Typuslokalität von Epactionotus aky.
Fig. 8: Arroyo Fortaleza, Misiones, Argentina, downstream the bridge of RP 21.
Fig. 8: Arroyo Fortaleza, Misiones, Argentina, flussabwärts der Brücke von RP 21.
88
3.8. Behaviour in aquarium
Epactionotus aky is reported to behave just as
most hypoptopomatine species which have
been known in aquaria for many years. It is a
peaceful species that usually hangs on the
trunks of Echinodorus sp. or similar aquari-
um plants which they can grap with their pel-
vic fins in a handlike manner. Although kept
by specialists in breeding loricariids during
more than a year, no attempts to reproduce
could be observed. The bright green colour
vanished during the first months and chan-
ged to brownish, but green reappeared for
short whiles. These colour changes seem to
happen due to mood and/or interindividual
relationships; the keepers exclude the possi-
bility that food or water chemistry could have
been the cause of these changes.
4. Discussion
The four known synapomorphies of the
tribe Otothyrini (Schaefer 1998) are present
in the new species: fourth infraorbital ex-
panded ventrally; rostral plates with notch;
ventral preopercular margin reflected ven-
trally; and channel between metapterygoid
and lateral ethmoid deeper than 50 % of its
length.
Among all genera belonging to this tribe,
Eurycheilichthys, Hisonotus, Microlepidogaster,
Otothyris, Parotocinclus, Pseudotocinclus, Pseudo-
tothyris, and Schizolecis, one undescribed
genus, and Epactionotus (Reis & Schaefer,
1998), the new species may be included in
Epactionotus.
Epactionotus aky shares the three synapomor-
phies of the genus, neural spine of seventh
Fig. 9: Arroyo Fortaleza, Mi-
siones, Argentina, upstream the
bridge of RP 21.
Fig. 9: Arroyo Fortaleza, Mi-
siones, Argentinien, flussaufwärts
der Brücke von RP 21.
89
Verh. Ges. Ichthyol. Bd. 4, 2004
vertebra not contacting nuchal plate dorsally,
first dorsal proximal radial contacting eighth
vertebra, and absence of expanded fleshy flap
on dorsal surface of first pelvic-fin ray of
males. Epactionotus aky also shares one of
the two additional characters, as light stripes
on head and trunk, but E. aky lacks the acces-
sory teeth.
The genus Epactionotus includes E. bilineatus,
E. itaimbezinho, E. gracilis (Reis & Schaefer,
1998), and E. aky described herein.
The number of lateral plates in E. aky (21-
23) is lower than that present in remaining
species of the genus (E. bilineatus 26-29, E.
itaimbezinho 27-29, and E. gracilis 27-31).
Epactionotus aky is differentiated from E. bili-
neatus, E. itaimbezinho, and E. gracilis by the
ventral surface completely covered with plate-
lets and the absence of unpaired predorsal
plates. The cleithral width, a measurement
that clearly separates the species of Epactiono-
tus (Reis & Schaefer, 1998), is not useful to
distinguish E. aky.
The three species of the genus Epactionotus
were described from coastal streams of
southern Brazil (Reis and Schaefer 1998).
Epactionotus aky comes from Uruguay river
basin, fact that enlarges the previously known
geographical distribution of the genus.
Acknowledgments
Authors thank C. Tremouilles (Museo de
La Plata) for help with drawings, Comisión
de Investigaciones Científicas de la Provin-
cia de Buenos Aires for support to JRC, M.
Rinas (Ministerio de Ecología de Misiones)
for collecting permissions, the board and
Fig. 10:Map showing
the collecting localities
of Epactionotus aky, 1:
Arroyo Garibaldi (type
locality); 2: Arroyo
Fortaleza.
Fig. 10:Karte mit den
Fundorten von Epactio-
notus aky, 1: Arroyo Ga-
ribaldi (Typuslokalität);
2: Arroyo Fortaleza.
90
members of GfI (Ichthyological Society,
German language area) for partly funding
the collection at Arroyo Fortaleza.
An earlier version of this paper benefitted
from critical comments of an anonymus re-
viewer and Dr. Hartmut Greven.
We also thank the German aquarists I. Seidel
and S. Hetz for their efforts to obtain more
information about the species in captivity. Fi-
gures 4 and 5 have been provided by I. Seidel.
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