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Copeia,
1991(2),
pp. 323-328
Rivulus immaculatus,
a New Killifish from Venezuela
(Cyprinodontiformes,
Rivulidae)
JAMIE
E. THOMERSON,
LEO
G. NICO
AND DONALD C. TAPHORN
Rivulus immaculatus n. sp. is described from small upper tributaries of the Rio
Venamo (Essequibo River drainage) in the Sierra Urapan Tepuy, Estado Bolivar,
Venezuela. It fits Parenti's definition of her informal group "Rivulus," but it is
a non-annual species. Females are marked with many scattered dark dots, but
they do not have a "rivulus spot." Males have conspicuous black margins on
their unpaired fins, and two or three contact organs on the margin of each lateral
body scale. Specimens were collected from cascading clear-water mountain
streams, pH 6.5, temperature 21.5-24 C. Rivulus magdalenae, which the new
species somewhat resembles, and R. bondi also fit Parenti's "Rivulus" definition,
but R. waimacui, R. cryptocallus, and R. deltaphilus are confounding.
Se describe Rivulus immaculatus de pequeiios alfluentes del Rio Venamo (cuen-
ca del Rio Esequibo) del la Serrania Urapan Tepui, del estado Bolivar, en el
sureste de Venezuela. Rivulus immaculatus cabe in el grupo "Rivulus" propuesta
por Parenti, pero no es una especie anual. Las hembras se caracterizan por
numerosos puntos negros en los costados del cuerpo, pero carecen de la mancha
ocelada en el pedunculo caudal superior que tipifica la mayoria de las hembras
del genero Rivulus. En los machos las aletas impares tienen bordes negros, y
tienen dos o tres organos de contacto en las escamas de los costados. Los ejem-
plares fueron colectados de cascadas cristalinas en las montafias con agua re-
lativamente fria (21,5 a 24 grados C) y de un pH de 6,5. La parecida especie, R.
magdalenae, y R. bondi tambien son miembros del grupo "Rivulus" como difinido
por Parenti, pero R. waimacui, R. cryptocallus, y R. deltaphilus no concordan
bien.
THE Neotropical aplocheiloid killifish genus
Rivulus Poey includes some 65 nominal
species (Lazara, 1984, 1986), and a number of
unidentified or undescribed forms are known
to aquarists and ichthyologists. The latest at-
tempt at a comprehensive revisionary study of
the genus was published by Hoedeman (1959,
1961), who recognized 45 nominal forms, but
was able to examine material of only 16. Fur-
thermore, it is likely that several of Hoedeman's
identifications were incorrect. Because species
of Rivulus are morphologically conservative,
with few clear-cut interspecific differences in
body shape or meristic characters, Hoedeman
(1961) used head squamation patterns to define
groups of related species. Unfortunately, this
character is not as useful as he had hoped (Tap-
horn and Thomerson, 1978; Parenti, 1981), and
the reality of his major subgeneric groups is not
well established.
Some 27 species of Rivulus have been de-
scribed since 1961 (Lazara, 1984, 1986), form-
ing a catalog of distinctive forms that has con-
tributed little to our understanding of rivulid
phylogeny. Even so, this effort is well justified
by the rapid loss of Neotropical biodiversity,
and has served the needs of killifish hobbyists
and regional biologists.
Parenti (1981), in her phylogenetic analysis
of the killifishes, places the New World aplo-
cheiloid killifishes in the putative monophyletic
family Rivulidae. Parenti examined only five
species of nominal Rivulus: R. cylindraceus
(the
type species), R. marmoratus,
R. tenuis, R. harti,
and R. stellifer. She characterized the first three
species as having ossified first interhyal ele-
ments, six pelvic-fin rays, and rounded dorsal
and anal fins in both sexes; and the latter two
species as having unossified interhyal elements,
seven pelvic-fin rays, and males with somewhat
elongate dorsal and anal fins. She retained Ri-
vulus as the generic name for the monophyletic
group including the first three species, and rec-
ognized this redefined Rivulus as the plesiom-
orphous sister group of the rest of the Rivuli-
dae. She used "Rivulus" as an informal name
? 1991 by the American Society of Ichthyologists and Herpetologists
COPEIA, 1991, NO. 2
Fig. 1. Rivulus immaculatus
n. sp.: A) Holotype, MBUCV 19092, female, 53.6 mm; B) Allotype, MBUCV
20290, male, 52.2 mm.
for a group including R. harti and R. stellifer,
and interpreted possession of unossified inter-
hyal elements and seven pelvic-fin rays as syn-
apomorphies linking "Rivulus" and the more
advanced rivulid genera, for example, Pterole-
bias and Cynolebias.
In addition to R. stellifer and R. harti, R. bondi
Schultz, R. magdalenae Eigenmann and Henn,
the new species described here, and probably
R. holmiae Eigenmann would fall into Parenti's
"Rivulus." On the other hand, we find wide
variation in the number of pelvic-fin rays, often
within a single individual, in other rivulus spe-
cies; such observations do not support formal
recognition of "Rivulus." We have thus re-
ferred the new species to Rivulus Poey sensu
lato, as it was understood prior to the work of
Parenti (1981).
METHODS
Standard length (SL) is used throughout.
Measurements were made with Helios dial cal-
ipers. Measurements and counts follow Hoede-
man (1959), with the exception that head depth
(HD) was measured at the posterior margin of
the preopercle. Measurements not taken by
Hoedeman include prepelvic-fin insertion length
(PP2L), snout length (SnL), and orbit diameter
(OD). Greatest body depth (GBD) is as mea-
sured by Hoedeman; not body depth at the
anal-fin insertion. Ratios are expressed in thou-
sandths so that the reader can reconstruct mea-
surements to the precision with which we re-
corded them. Fin-ray counts were made on
preserved specimens using a dissecting micro-
scope, with light transmitted through the fins,
and include all discernable fin-rays. Four para-
types, and comparative material as listed, were
cleared and stained following Dingerkus and
Uhler (1977). Color descriptions are based on
field notes, color slides and observations of wild-
caught fish in the aquarium. Institutional ab-
breviations follow Leviton et al. (1985).
Rivulus immaculatus n. sp.
Fig. 1.
Holotype.-MBUCV 19092, female, 53.6 mm,
La Mejicana, km 105, road between El Dorado
and Sta. Elena de Uairen, Bolivar State, Ven-
ezuela, 06'03'N, 61'23'W, 26 July 1966 Mosco,
R. Campos-V., C. J. Sanchez and L. Juare (Fig.
1A).
324
THOMERSON ET AL.-NEW RIVULUS
Allotype.-MBUCV 20290, male, 52.2 mm, data
as for holotype (Fig. 1B).
Paratypes.-MBUCV 3983, 33, 22.7-51.3 mm;
FMNH 99282, 2, 55.3 and 55.8 mm; FMNH
99282, 4 (cleared and stained) 28.5, 29.0, 44.6,
51.4; USNM 308411, 2, 52.1 and 59.6 mm;
CAS 69412, 2, 48.7 and 49.1 mm; data as for
holotype. MCNG 18987, male, 43.8 mm, km
110, road between El Dorado and Sta. Elena de
Uairen, 18 Aug. 1988,J. Thomerson, L. Nico,
E. Hoigne and E. Sutton. MCNG 21355,6, 32.6-
54.1 mm, km 110, road between El Dorado and
Sta. Elena de Uairen, 21 July 1988, J. Thom-
erson, D. Taphorn, L. Balbas.
Diagnosis.-The new species differs from some
other species of Rivulus by having unossified
interhyals, usually seven pelvic-fin rays, and
slightly elongate dorsal and anal fins in both
sexes. It differs from species of Rivulus known
to have the above combination of characters by
lack of the "rivulus spot" in females of all sizes,
body pattern of scattered dark dots in females,
black margins on the unpaired and pelvic fins
in males, and presence in males of two or three
contact organs on the margins of lateral body
scales. Miller and Hubbs (1974) reported that
in R. robustus,
which usually has seven pelvic-fin
rays, males have a single contact organ per scale.
Description.-Meristic and morphometric val-
ues are given in Table 1. In addition to these
data, the four cleared and stained paratopo-
types (FMNH 99282) have unossified interhyal
elements, 13-15 abdominal vertebrae + 19-20
caudal vertebrae to give 33 or 34 total verte-
brae. Dorsal fin inserted over vertebra 20, 21
or 22; anal fin inserted below first abdominal
vertebra (centra 14, 15 or 16), to give five or
six vertebra between origins of dorsal and anal
fins.
Pigment pattern of preserved specimens is
shown in Figure 1. Life colors of females similar
to Figure 1
A, but lateral spots relatively darker
and more sharply defined. Number and density
of lateral spots increasing as females grow.
Ground color grey to brownish-grey, belly light
grey to dusky white. Fins more hyaline than
seen in preserved specimens. In life, anterior
third of body of male yellowish tan, grading to
dark grey-brown dorsally and posteriorly; lat-
erally color darkens to dark grey, with uniform
green to steel-blue iridescent sheen. Scattered
burnt-orange spots covering one to several scale
centers distributed along ventrolateral surface
of body from about tip of depressed pectoral
fin onto caudal peduncle; spots represented by
lighter scales on preserved male (Fig. 1B). Fins
light grey, with more hyaline areas toward prox-
imal tip of anal fin and in center of caudal fin.
Band of dusky yellow paralleling black margin
of anal fin. Unpaired fins unevenly margined
with jet black; these margins of allotype (Fig.
1B) less developed than those of most males.
One live male with hyaline margin of anal fin.
Central portion of caudal fin margin hyaline in
most males, but one live male with jet-black
border of the caudal fin wider in center than
above and below. Pelvic fins with dusky to black
margin in males. Unpaired fins of males with
bluish sheen in reflected light.
Large males with two or three small spicule-
like contact organs on margin of each lateral
body scale; organs absent on scales on caudal
peduncle, dorsum and belly. Holotype with
d-pattern head squamation, with f-scale on one
side also exposed. Allotype with d-pattern, one
paratopotype with d-e', one with e-d' and four
other with e-pattern.
Etymology.-The specific epithet, immaculatus,
is derived from the Latin in, meaning "with-
out," + maculatus, meaning "spotted" (i.e.,
"unspotted"), in reference to the absence of the
"rivulus spot" in this species.
DISCUSSION
Rivulus immaculatus is a large, distinctively
patterned rivulus that falls into Parenti's (1981)
"Rivulus" by having unossified interhyal ele-
ments, usually seven pelvic-fin rays, and slightly
elongate dorsal- and anal-fin rays in both sexes.
Parenti speculated that all "Rivulus" species
would prove to be annual fishes (Myers, 1952);
but, as Fromm (1986) pointed out, there is little
evidence for annualism in what we know of rivu-
lus life histories. Annualism in "R." stellifer is
well known (Thomerson and Turner, 1973; Ko-
ran, 1986), but neither "R." harti (Fromm, 1986;
pers. obs.) nor the new species described here,
show any evidence of embryonic developmental
diapauses, the defining characteristic of an an-
nual killifish (Wourms, 1972a, 1972b, 1972c).
Rivulus bondi Schultz and R. magdalenae Eigen-
mann and Henn also fit Parenti's "Rivulus" def-
inition. We have cultured both these species
through several generations, and the latter spe-
325
COPEIA, 1991, NO. 2
TABLE 1. MEASUREMENTS, PROPORTIONS, AND COUNTS FOR 10 MEMBERS OF THE TYPE SERIES OF Rivulus
immaculatus N. SP.
Character Holotype Allotype Minimum Average Maximum
Sex female male (five of each sex)
SL mm 53.6 52.2 44.6 60.0 55.8
TL/SL 1.231 1.257 1.231 1.256 1.274
PDL/SL 0.603 0.587 0.586 0.594 0.603
PAL/SL (F) 0.498 0.476 0.471 0.489 0.506
PP2L/SL (F) 0.414 0.390 0.390 0.400 0.415
GBD/SL 0.159 0.175 0.154 0.170 0.184
CPD/S 0.105 0.101 0.094 0.104 0.117
P1L/SL 0.141 0.155 0.128 0.145 0.162
P2L/SL 0.075 0.087 0.069 0.078 0.087
DL/SL 0.165 0.178 0.141 0.170 0.184
DB/SL 0.079 0.088 0.074 0.079 0.088
AL/SL (M) 0.250 0.268 0.243 0.264 0.284
AB/SL (M) 0.161 0.174 0.153 0.163 0.178
HL/SL (F) 0.246 0.255 0.238 0.253 0.269
HW/HL 0.720 0.684 0.667 0.702 0.743
HD/HL 0.549 0.575 0.517 0.581 0.677
OD/HL 0.303 0.312 0.288 0.319 0.328
SnL/HL 0.201 0.199 0.177 0.210 0.263
Dorsal-fin rays Anal-fin rays
Number of rays 8 9* 12 14* 15
Specimens 3 7 1 4 5
Pectoral-fin rays Pelvic-fin rays
Number of rays 15* 6 7*
Specimens 10 1 9
Lateral scales Transverse scales
Number of scales 34 37 38* 39 40 10* 11
Specimens 1 2 3 1 3 8 2
Predorsal scales (8 specimens only)
Number of scales 26 27 28* 29 30
Specimens 1 1 3 2 1
(M) and (F) indicate that five of the six largest values were from males or females, respectively. Counts for Holotype are italicized, counts for
Allotype indicated by *.
cies has been cultured by aquarists for more
than 20 yr (R. harti even longer), and we are
unaware of any report that their eggs undergo
diapause. Thus, except for "R." stelifer, Par-
enti's (1981) suggestion of a correlation be-
tween "Rivulus" and annual life history is un-
supported.
Embryonic development and survival over
periods as long as 60 d were reported for R.
urophthalnus by Vaz Ferreira and Sierra (1973),
and indirect evidence of embryonic diapause
was reported for R. marmoratus
(one of the spe-
cies retained in Rivulus by Parenti) by Ritchie
and Davis (1986) and for R. luelingi by Liiling
(1984).
Rivulus waimacui, R. deltaphilus, and R. cryp-
tocallus all have highly variable numbers of pel-
vic-fin rays (Table 2). Because the latter two
species lack ossified interhyals (condition in the
former unknown), "Rivulus" predicts that they
should ordinarily have seven pelvic-fin rays.
Thus the "Rivulus" hypothesis of relationship
is not well supported by a concordant synapo-
morphy of seven pelvic-fin rays, nor is seven or
326
THOMERSON ET AL.-NEW RIVULUS
TABLE 2. PELVIC-FIN RAY COUNTS ON SEVERAL
Rivulus SPECIES
WITH UNOSSIFIED INTERHYALS. Presence of
unossified interhyals not verified for Rivulus holmiae
or R. waimacui. Contrary to Parenti (1981), these R. tenuis
specimens
had unossified
interhyals.
Number of pelvic-fin rays
Species n 5,5 5,6 6,6 6,7 7,7 7,8 8,8
R. harti 13 13
R. stellifer 8 5 21
R. immaculatus
n. sp. 10 1 9
R. bondi 41 39 2
R. magdalenae 4 4
R. deltaphilus 13 1 2 3 4
R. cryptocallus 4 1 2 1
R. tenuis 7 1 6
R. holmiae 10 1 1 8
R. waimacui 7 3 1 3
more pelvic-fin rays a unique synapomorphy for
the more advanced rivulid genera.
Females of Rivulus species are traditionally
thought of as having a caudal "rivulus spot"
lacking in males (Parenti, 1981), but of the 47
forms analyzed by Fromm (1986; Table 1), 10
are said to lack the rivulus spot in both sexes.
In some species (i.e., R. harti; pers. obs.) all ju-
veniles have rivulus spots. These are lost in the
process of sexual differentation in males, and
may be lost by very large females. The rivulus
spot is not present in either sex ofR. immaculatus
at any life stage.
The type series of R. immaculatus was taken
with rotenone. Other fishes in the same collec-
tion included trichomycterid catfishes, an au-
chenipterid catfish, Ancistrus sp. (Loricariidae),
Deuterodon af. potaroensis
(Characidae), and the
lebiasinids Lebiasina sp. and Pyrrhulina sp. In
1988, R. immaculatus was recollected at the type
locality (km 105) and from two other small
streams crossing the road at km 103 and km
110. It was not taken from a stream at km 108.
The km 11-0 site was recollected in 1989. All
collection sites were between Piedra de La Vir-
gen to the north and Salto El Danto to the south,
in the region known as "La Escalera" (aquarists
call this species the "La Escalaera rivulus").
These clear-water (pH 6.5, temperature 21.5-
24 C), high-gradient streams, tributaries of the
Rio Uaia that drain the eastern slope of the
Sierra Urapan Tepuy, are part of the Essequibo
River drainage. At the collection sites, they drop
approx. 30 m/100 m, with cascades over many
boulders and rock ledges. The 1988 and 1989
collections were made with handnets. With the
exception of MCNG 18987, the 19 fish collect-
ed in 1988 were pooled and kept alive for fur-
ther study. A few trichomycterid catfishes that
strongly resembled female R. immaculatus in
body size, shape and pattern, were also taken
in 1988 and 1989.
Guts of the cleared and stained specimens
(FMNH 99282) contained several ants and small
wasps. Fecundity ofR. immaculatus
in the aquar-
ium seems low in comparison to other rivulus
species (Fromm, 1986). Eggs are similar in ap-
pearance, size (1.8-2.3 mm diameter) and de-
velopment to eggs of R. harti, but fry have grown
slowly in comparison to fry of R. harti raised
under similar conditions.
COMPARATIVE MATERIAL EXAMINED
The following collections include the speci-
mens listed in Table 2. Rivulus harti:
Trinidad-
CAS 69413 (1), SU24044 (2), 64066 (16);
FMNH 50096 (3), 50098 (4), 50099 (8, 2 cleared
and stained), 50100 (10, 2 cleared and stained),
58856 (1); MCNG 8238 (9). Rivulus stellifer:
Venezuela-FMNH 99513 (2 cleared and
stained), MCNG 23646 (6 cleared and stained).
Rivulus bondi: Venezuela-MCNG 23647 (2
cleared and stained), 16758 (23), 16782 (3),
17163 (32). Rivulus magdalenae: Colombia-
AMNH 57471 (12, 4 cleared and stained). Rivu-
lus deltaphilus: Venezuela-MCNG 23648 (9
cleared and stained), 17244 (5 cleared and
stained). Rivulus cryptocallus: Martinique-
ANSP 128517 (10, 4 cleared and stained). Rivu-
lus holniae: Guyana-CAS SU21777 (1), 44217
(4). FMNH 7519 (1), 50192 (1), 52711 (4), 53535
327
COPEIA, 1991, NO. 2
(1). Rivulus waimacui:
Guyana-CAS 11760 (5),
FMNH 52712 (2), 53536 (1). Rivulus tenuis: Be-
lize-FMNH 99514 (2 cleared and stained),
99515 (5 cleared and stained).
ACKNOWLEDGMENTS
We thank F. Mago Leccia, H. Lopez Rojas,
and A. Machado A. for permission to examine
material, and for many other courtesies ex-
tended to us. We also thank curators at AMNH,
ANSP, CAS and FMNH for loan of material
and for other courtesies. L. Balbas, E. Hoigne
and E. Sutton assisted with field work. We thank
the Oficina Nacional De Pesca del Ministerio
de Agricultura y Cria for permission to make
scientific collections in Venezuela. This mate-
rial is based work supported by the Graduate
School and the School of Sciences, Southern
Illinois University at Edwardsville, CONICIT
proyecto de investigacion #S-1978 and by the
National Science Foundation under Grant No.
INT-8901678.
LITERATURE
CITED
DINGERKUS,
G., AND L. D. UHLER. 1977. Enzyme
clearing of alcian blue stained whole small verte-
brates for demonstration
of cartilage. Stain Tech.
52(4):229-232.
FROMM,
D. 1986. Rivulus as live animals. J. Amer.
Killifish Assn. 19(1):4-53.
HOEDEMAN,
J. J. 1959. Rivulid fishes of Suriname
and other Guyanas,
with a preliminary
review of
the genus Rivulus.
Studies of Suriname and other
Guyanas
3(7):44-98.
. 1961. Studies on cyprinodontiform
fishes.
Preliminary
key to the species
and subspecies
of the
genus Rivulus.
Bull. Aquat. Biol. 2(18):65-74.
KORAN, D. 1986. Rivulus stellifer Thomerson and
Turner, 1973;
the annual
Rivulus.
J. Amer. Killifish
Assn. 19(1):97-102.
LAZARA, K. J. 1984. The killifish master index: a
checklist of oviparous cyprinodontiform fishes.
American Killifish
Association, Cincinatti,
Ohio.
. 1986. A review of Rivulus Poey, 1860. J.
Amer. Killifish
Assn. 19(1):54-65.
LEVITON,
A. E., R. H. GIBBs,JR., E. HEAL
AND C. E.
DAWSON. 1985. Standards in herpetology
and ich-
thyology: Part I. Standard
symbolic codes for in-
stitutional resource collection in herpetology and
ichthyology. Copeia 1985(3):802-832.
LULING,
K. H. 1984. Der Biotop von Rivulus luelingi
Seegers, 1984 (Pisces, Rivulinae) suestlich vonJoin-
ville (Santa Catarina). Bonn Zool. Beitr. 34(4):343-
350.
MILLER,
R. R., AND C. L. HUBBS. 1974. Rivulus ro-
bustus, a new cyprinodontid fish from southeastern
Mexico. Copeia 1974(4):865-869.
MYERS,
G. S. 1952. Annual fishes. Aquar. J., San
Francisco 23(7):125-141.
PARENTI,
L. R. 1981. A phylogenetic and biogeo-
graphic analysis of cyprinodontiform fishes (Te-
leostei, Atherinomorpha). Bull. Amer. Mus. Nat.
Hist. 168:335-557.
RITCHIE, S. A., AND W. P. DAVIS. 1986. Evidence for
embryonic diapause in Rivulus marmoratus: labo-
ratory and field observations. J. Amer. Killifish Assn.
19(1):103-108.
TAPHORN,
D. C., AND
J. E. THOMERSON.
1978. A
revision of the South American cyprinodont fishes
of the genera Rachovia and Austrofundulus,
with the
description of a new genus. Acta. Biol. Venez.
9(4):377-452.
THOMERSON,J.
E., AND
B.J. TURNER. 1973. Rivulus
stellifer, a new species of annual killifish from the
Orinoco Basin of Venezuela. Copeia 1973(4):783-
787.
VAZ-FERREIRA,
R., AND
B. SIERRA. 1973. Notas sobre
comportamiento y sobre desarrollo con diapausa
de Rivulus uropthalmus Gunther, 1866. Bol. Soc.
Zool. Uruguay 2:43-48.
WOURMS,J.
P. 1972a. Developmental biology of fish-
es. I. Stages in the normal development of Austro-
fundulus myersi
Dahl. J. Exp. Zool. 182:143-168.
. 1972b. Developmental biology of fishes. II.
Naturally occurring dispersion and reaggregation
of blastomeres
during the development of annual
fish eggs. Ibid. 182:169-200.
. 1972c. Developmental biology of fishes. III.
Pre-embryonic and embryonic diapause of variable
duration
in the eggs of annual fishes. Ibid.
182:389-
414.
(JET) DEPARTMENT OF BIOLOGY, SOUTHERN IL-
LINOIS UNIVERSITY AT EDWARDSVILLE, ED-
WARDSVILLE, ILLINOIS 62026; (LGN) DE-
PARTMENT OF ZOOLOGY, UNIVERSITY OF
FLORIDA, GAINESVILLE, FLORIDA 32611; AND
(DCT) MUSEO DE CIENCIAS NATURALES,
UNELLEZ, GUANARE, PORTUGUESA, 3310,
VENEZUELA.
Accepted 5 June 1990.
328
