A J Almeida

M Biscoito

M Segonzac

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15Vol. 10(1), 2001b
 New zoarcid fish species from deep-sea hydrothermal vents of the Atlantic
and Pacific Oceans
M. Biscoito1, M. Segonzac2 and A. J. Almeida3
1 IMAR - Museu Municipal do Funchal (História Natural), R. da Mouraria, 31, 9004-546 Funchal, Portugal
2 IFREMER, Centre de Brest, BP 70, 29280 Plouzané, France
3 IMAR – Laboratório Marítimo da Guia, Estrada do Guincho, 2750-642 CASCAIS, Portugal
 International Ridge-Crest Research: Biological Studies
Introduction
The fish family Zoarcidae has 45
genera, two of which have been re-
corded from active hydrothermal
vent fields, Pachycara Zugmayer,
1911 and Thermarces Rosenblatt &
Cohen, 1986.
The genus Pachycara contains
17 species occurring in the Pacific,
Atlantic, Antarctic and Indian
Oceans (Møller and Anderson,
2000).  Three of them, P. gymninium
Anderson and Peden, 1988, P. rimae
Anderson, 1989 and P. thermophil-
um Geistdoerfer, 1994, have been
collected in active deep-sea hydro-
thermal vents, the last two being
endemic to this type of environment
(Tunnicliffe et al., 1998).
To date, only one species of
Pachycara (P. thermophilum) has
been recorded from the Mid-Atlan-
tic Ridge hydrothermal vents. This
species was originally described
from Snake Pit (23°22´N, 3,480 m)
and subsequently found at Logatch-
ev (14°45´N, 3,000 m), TAG (26°N,
3,700 m) and Broken Spur (29°N,
3,020 m) (Parin, 1995; Anderson and
Bluhm, 1996; Geistdoerfer, 1997).
In contrast with Pachycara,
Thermarces has only 3 nominal spe-
cies, all of them restricted to chem-
osynthetically-driven environ-
ments: Thermarces cerberus Rosen-
blatt & Cohen, 1986, from 21°N,
13°N, 11°N and 9°N, in the East
Pacific Rise and also in the Galapa-
gos Ridge, T. andersoni Rosenblatt
& Cohen, 1986 from 13°N EPR [con-
sidered a doubtful species (Ander-
son, 1994)], and T. pelophilum
Geistdoerfer, 1999 from the Barba-
dos accretionary complex.
Collection of specimens
Mid-Atlantic Ridge  - (Pachycara
n. sp.).
In 1997 the newly discovered
Rainbow vent field, in the Mid-At-
lantic Ridge (36°13.8´N, 2270 – 2320
m) was first visited by biologists,
during Nautile’s diving cruise
MARVEL (Aug – Sept 1997, PIs: D.
Desbruyères and A-M. Alayse). In
one of the dives (PL 1197, 23/8/1997)
a zoarcid fish was seen dwelling
among mussels (Fig. 1). At that time
it was impossible to collect a speci-
men. One year later, during AMORES
cruise PICO (Jun – Jul 1998, PI: D.
Desbruyères) and the Franco-Por-
tuguese AMAR (Luis Mendes-Vic-
tor, FCT contract PRAXIS/2/2.1/
MAR/1748/95), cruise SALDANHA
(July 1998, PI: F. Barriga), Rainbow
vent field was revisited and explored
with Nautile. This time 6 specimens
were collected with the submersi-
ble’s slurp-gun, and preserved for
identification.
Figure 1. Pachycara sp. n. amongst mussels at Rainbow vent field. Photograph
taken from video recorded by the Nautile during MARVEL cruise (Atlantic
Ocean).
InterRidge News16
It is undoubtedly very closely
related to P. thermophilum Geistdo-
erfer, 1994, which also occurs in the
same type of environment, 1,100 km
south of Rainbow vent field. The
first major difference found in our
specimens is the presence of two
branches of the lateral line (medium-
lateral only in P. thermophilum).
Other differences include the
interorbitary width, which is con-
sistently higher in our specimens
than in P. thermophilum and the
number of caudal vertebrae and dor-
sal and anal fin rays, whose counts
are also higher in our specimens. In
fact the vertebral formula do not
coincide with any of the other 17
described species of Pachycara,
with the exception of P. bulbiceps,
Garman,1899, which can easily be
separated from our new species by
the absence of pelvic fins.
Colour, uniformly light brown
with whitish scale pockets, gives
the specimens a mottled appearance.
Outer margins of dorsal, anal and
pectoral fins are dark. Eyes bluish
and abdomen dark bluish brown. On
video images taken by the submers-
ible, the specimens appear almost
white, with dark dorsal, anal and
pectoral fins.
To date, this species is only
known from Rainbow hydrothermal
vent field, Mid-Atlantic Ridge
(36°13.8’N, 2 270 – 2 320 m).
Thermarces n. sp. (Fig. 4)
This new species, being de-
scribed elsewhere, is diagnosed by
the following characters: vertebral
formula 26-27+61=87-88, 79-81 dor-
sal fin rays, 15 pectoral fin rays and
four teeth in a single row on vomer.
Our two specimens can easily be
separated from T. cerberus and T.
pelophilum by the above mentioned
characters. Moreover, in all speci-
mens of T. cerberus examined, teeth
on vomer are not only more numer-
ous, but always arranged in a patch,
and not in a single row. Although
colour should not be used as a diag-
nostic characteristic, it is worthwhile
noting that our two specimens were
uniformly dusky brown, when cap-
Figure 2. Thermarces sp. n. at 9°50’N, EPR. Photograph taken from video
recorded by the Nautile during HOT’96 cruise (Pacific Ocean).
Figure 3. Pachycara sp. n. Drawing of the holotype, 247 mm SL.
Figure 4. Thermarces sp. n. Drawing of the holotype, 375 mm SL.
Two specimens were collected
with a baited fish trap during HOT 96
cruise (Feb – Mar 1996, PI: F. Gaill.)
(Nautile dive PL 1079, 08/03/1996) at
the East Wall site (9°50.6’N, 2530 m)
among mussels (many of them dead)
(Fig. 2).
Results
Pachycara n. sp. (Fig. 3)
This new species, being de-
scribed elsewhere, is distinguished
by the following characters: 31-
32+85-86=117 vertebrae, gill rakers
2+14, dorsal fin with 109 rays, anal
fin with 90-91 rays, pelvic fins
present, with 2 rays, their length
11.4-13.5% HL, lateral line with me-
dium-lateral and ventral branches,
the latter very inconspicuous,
scales absent from cheek, nape and
abdomen.
 International Ridge-Crest Research: Biological Studies: Biscoito et al., cont ....
East Pacific Rise, 9°N (Thermarces n. sp.).
17Vol. 10(1), 2001b
tured. After four years in preserva-
tive, they have more or less kept the
same colour. On the contrary, T.
cerberus when fresh, are very light
yellowish brown, sometimes mot-
tled. After an equivalent time in pre-
servative they become colourless.
Another remarkable difference is the
size of the body. Thermarces n. sp.
is noticeable more corpulent than T.
cerberus. Both differences, in col-
our and size, were confirmed by vid-
eo observations.
This new species is only known
with certainty from 9°N, 2520 m, East
Pacific Rise.
Ecological information
Pachycara n. sp. lives well in-
side the active areas, usually
amongst mussels and in between
small boulders at the base of chim-
neys. Direct observations showed
that these fish are usually solitary,
the minimum observed distance be-
tween two specimens being 1.5 m.
Consequently they seem not to be
very abundant. In general they are
not very active, unless disturbed.
The temperature measured with
Nautile’s probe in the exact place
where a specimen was collected at
Rainbow (marker PP37, 2287 m), was
15°C. Sea water temperature outside
the active site was 3.8°C.
Stomach content analysis in one
specimen revealed the remains of
shrimp Rimicaris exoculata (Crus-
tacea, Decapoda, Bresiliidae) to-
gether with orange-brown particles
of oxides, very characteristic of Rain-
bow vent field. Based on the infor-
mation available, Pachycara n. sp.
can probably be considered endem-
ic to Rainbow.
Thermarces n. sp. collected at
East Wall (EPR, 9°N) lives inside or
in the periphery of mussel beds
(Bathymodiolus thermophilus) cov-
ering certain depressions on the
basalts, bathed by mild temperature
hydrothermal fluids (6.7°C) coming
from diffuse vents (sea water tem-
perature was 1.7°C). At this site the
density of these fish was very low
(4-5 individuals over several tens of
square metres).
During the mission HOPE 99 (Apr
– May 1999, PI: F. H. Lallier), great
effort was made to obtain more spec-
imens of this new species. All vent
zoarcids collected at 13° and 9°N
belonged to the species T. cerberus,
which live in great numbers amongst
clumps of Riftia pachyptila. On vid-
eo images, all specimens observed
showed the typical whitish coloura-
tion, leading us to conclude that
they were all T. cerberus. At 9°N,
none of the specimens recorded on
video during the mission could be
assigned to this new species, nei-
ther at East Wall, nor at various
other sites extending 5 km further
north.
Conclusions
The finding of these new species
reinforces the position of the family
Zoarcidae, as the dominant fish taxon
in the hydrothermal vent environment.
In the description of Thermarces n.
sp., the authors will deal with the affin-
ities of the new species with the T.
cerberus/T. andersoni complex. In
future missions to the EPR, emphasis
should also be put in obtaining more
specimens from Thermarces n. sp.,
not only to obtain material for genetic
analyses in order to establish the rela-
tionship between the two species, but
also to ascertain their distribution.
We also expect to be able to collect
more specimens of Pachycara n. sp.
during the forthcoming ATOS cruise,
scheduled for June 2001, in order to
obtain material for genetic analyses.
Acknowledgements
The authors are indebted to
Françoise Gaill, Daniel Desbruyères,
Fernando Barriga and François Lalli-
er, Chief-Scientists of HOT 96, MAR-
VEL and PICO, SALDANHA and
HOPE 99 cruises respectively, for the
invitations to take part in these cruis-
es and collaboration on board. Thanks
are also due to the Captains and crews
of the French N/O Nadir and N/O
L’Atalante, the pilots and technicians
of the deep submersible Nautile, and
several colleagues for all their help at
various levels during the cruises. Hele-
na Encarnação of the Museu Munci-
pal do Funchal (História Natural) made
the fine illustrations.
This work was made possible
through funds obtained from the EU-
MAST3 funded AMORES (Azores
MOR Ecosystem Studies, Coordina-
tor D. Desbruyères, MAST III con-
tract MAS3-CT95-0040.) (Contract n°
MAS3 95-0040), Portuguese PRAXIS
XXI AMAR Project (Contract n°
PRAXIS/2/2.1/MAR/1748/95, and by
the URM 7 Ifremer and Dorsales Pro-
gramme. The examination of material
at the MNHN in Paris was sponsored
by the ICCTI-IFREMER Agreement in
Oceanology.
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 International Ridge-Crest Research: Biological Studies: Biscoito et al., cont ....


New zoarcid fish species from deep-sea hydrothermal vents of the Atlantic and Pacific Oceans

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New zoarcid fish species from deep-sea hydrothermal vents of the Atlantic and Pacific Oceans

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