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Sistema de Información Científica
Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
120
MAR 2005, VOL. 30 Nº 3
Keywords: /
Eleginops /
Eleginopidae / Feeding Shifts / Osmoregulation / South America /
Plano sandalias 5 talón mujeres oro US4 2 Plata CN33 EU34 UK2 Otros Las Casual 5 Otros PU de 4 verano Confort Received: 05/10/2004. Modified: 01/11/2005. Accepted: 02/04/2005.
Héctor Pavés.
Marine Biologist and Doctoral Student, Universidad Austral de Chile (UACh).
Germán Pequeño.
Ph.D., Oregon State University, USA. Professor, Instituto de Zoología
“Ernst F. Kilian”, Universidad Austral de Chile. Address: Casilla 567, Valdivia, Chile. e-mail: gpequeno@uach.cl
Carlos Bertrán.
M.Sc., UACh. Doctor, Universidad de Concepción, Chile. Professor, UACh.
Luis Vargas.
Marine Biologist, UACh. Doctoral Student, Universidad de Cadiz, Spain.
LIMNETIC FEEDING IN
Eleginops maclovinus
(VALENCIENNES, 1830)
IN THE VALDIVIA RIVER, CHILE
HÉCTOR PAVÉS, GERMÁN PEQUEÑO,
CARLOS BERTRÁN and LUIS VARGAS
leginops maclovinus
, Va-
lenciennes, 1830 is a
monotypic species of the
family Eleginopidae (Osteichthyes), sub-
order Notothenioidei. The species is
thought to be of Antarctic evolutionary
origin, and is one of the most euryther-
mic, euryhaline and stenobathic represen-
tative of the suborder (Pequeño, 1989).
This species is endemic to southern
Chile, southern Argentina and the Mal-
vinas Islands, where it occurs near oce-
anic beaches, and in large and small estu-
aries. In Chile it is found south of the
Aconcagua River (33ºS) and has been
caught in rivers of southern Chile, several
kilometers offshore of the river mouths
(eg. Valdivia River, this study), and over
20km upstream in low salinity (limnetic)
waters.
Previous observations of
the trophic relations of
E. maclovinus
had
been made on specimens obtained in ma-
rine and estuarine habitats. Although this
species has been generally considered as
an omnivorous predator, the literature re-
flects two contrasting variations on this
point, the first by Guzmán and Cam-
podónico (1973) and Gosztonyi (1979),
who postulated an ontogenetic change
from carnivorous behavior in early juve-
nile stages to a herbivorous one in adults.
The second opinion, held by Pequeño
(1979) and Turner (1988) is that the spe-
cies tended toward a carnivorous behavior
0378-1844/05/03/120-06 $ 3. 00/0
throughout its entire ontogenetic develop-
ment.
In the present study the
trophic relations between juveniles and
adults of
E. maclovinus
within a limnetic
habitat, namely the upper Valdivia River
estuary, are compared. It was also tested
whether
E. maclovinus
, the notothenioid
species that most commonly inhabits
fresh waters, preys upon typical freshwa-
ter species during its residence in this
habitat, and remains carnivorous as ob-
served in specimens studied from brack-
ish and marine waters. Parasitological
evidence obtained from the stomachs of
the fish is also used to evaluate the hy-
pothesis of carnivorous tendency in both
juveniles and adults of this species.
Materials and Methods
Sample collection
Samples of
E. maclovi-
nus
included 114 individuals obtained us-
ing a 1.75×30m gillnet with 32mm open-
ings. Catches were made from 17 to 20
March 2002, at Las Mulatas (39º50'S,
73º15'W), at a distance of about 16km
upstream from the Pacific Ocean, in the
Valdivia River estuary (Figure 1). Tidal
movement in this estuary takes place to
about 20km inland of the river's mouth,
and limits of salt water (salinity= 0.1‰)
reach about 14km inland. All the speci-
mens were measured for total length (TL,
live) and standard length (SL) using a
ruler graduated in millimeters. Weights
were obtained using a field balance
graduated to 0.1g. At the laboratory, the
fishes were initially fixed in 10% river
water formalin for 48h and stored in 70%
ETOH. The stomachs were removed from
each specimen and stored separately for
subsequent contents analysis.
Collection of bottom samples
Sampling of the bottom
fauna of the Valdivia River was carried
out at two stations, including Las Mulatas
and Los Pelúes (Figure 1). At each sta-
tion samples were obtained both near the
sandalias EU34 verano UK2 mujeres 5 de Confort Otros oro US4 5 2 Otros PU Casual Plata talón CN33 Las Plano 4 shore and at its deepest point, using cor-
ers hand-held by divers. Four replicate
samples were obtained at each sampling
point. These samples were collected on
the same dates as the fishes were.
Macrofauna were ini-
tially separated from the sediments using
a 0.5mm screen, fixed in 10% formalin,
and stored in 70% ETOH. These speci-
mens were subsequently separated under
a stereomicroscope and identified to the
closest possible taxonomic species level
using specialized keys. The species rich-
ness and relative abundance were deter-
mined on each of the samples (Morin,
1999). The samples were finally dried at
60ºC for 48h and weighed to determine
MAR 2005, VOL. 30 Nº 3
121
the approximate biomass per species in
each sample.
Stomach contents analysis
The determination of
stomach contents was made using a ste-
reomicroscope, aided by specialized
taxonomic identification keys (Stuardo,
1961; Yamaguti, 1961; Menzies, 1962;
Retamal, 1981), as well as with the aid
from the specialists from the Institutes
of Zoology and Botany at the Univer-
sidad Austral de Chile. The individuals
from the identified taxa were counted to
obtain the frequency distributions of spe-
cies and proportions of individual taxa
in each analyzed stomach (F: frequency
of occurrence per number of stomachs;
F%: frequency of occurrence expressed
in proportions of stomachs). The abun-
dance of prey items found indicated the
number of individuals of a given taxon
registered in all the samples analyzed
(N: abundance expressed per number of
individuals; N%: abundance expressed in
percentage of individuals).
Results
A total of 114 speci-
mens of
E. maclovinus
were obtained in
the samplings. These had a mean total
length (live) of 26.7cm (18-42cm, sd=
4.6cm) and a mean weight (live) of
224.9g (75-800g, sd= 146.7g). Most
specimens were immature males of 2-4
years of age (Gosztonyi, 1974; Calvo,
et
al
., 1992). The by-catch obtained in
sampling for
E. maclovinus
included the
salmoniformes
Oncorhynchus
mykiss
(exotic, introduced),
Galaxias maculatus
and
G. platei
, the smelts
Austromenidia
laticlava
and
Basilichthys
australis
(Atherinopsidae), and the cosmopolitan
mullet
Mugil cephalus
(Mugilidae).
Of all the
E. maclovinus
stomach samples, 103 (90%) could be
analyzed, while the remainder (11) were
in a degraded condition. The analyzed
specimens had mean total length (fixed)
of 25.0cm (18-40.1cm, sd= 3.3cm) and
their mean standard length was 22.0 cm
(15.5-30.2cm, sd= 2.8cm).
Almost all the samples
from which the complete digestive tract
could be extracted (93%, n=96) had
stomach contents present. In these it was
possible to identify species or high taxo-
nomic levels of plant and animal re-
mains. Only 7 (7%) of the stomachs
were empty. A total of 55 (53%) stom-
achs analyzed contained nematode para-
sites.
The analysis of the
stomach contents revealed a broad range
of food items, accompanied by appre-
ciable amounts of detritus such as sand
and rock grains (
eg
. schist, mica). Items
observed included algae, plant material,
gastropods, crustaceans, insects, and
fishes, mostly of estuarine or lacustrine
origin. Of the analyzed stomachs, 96
(93%) contained animal remains, and 89
(84%) contained plant remains (Table I).
The highest frequency group on the
TABLE I
FREQUENCY OF OCCURRENCE IN RELATION TO TOTAL NUMBER OF
STOMACHS ANALYZED (F, F%) AND NUMBER OF ITEMS (N, N%) IN THE
STOMACH CONTENTS OF
Eleginops maclovinus
IN THE VALDIVIA RIVER
Taxa
N
N%
F
F%
Crustacea
96
93.20
Corophiidae (Amphipoda)
59246
97.148
96
93.20
Tanaidacea (Malacostraca)
104
0.171
14
13.59
Ciprinidae (Ostracoda)
20
0.033
10
9.71
Hemigrapsus crenulatum
5
0.008
5
4.85
Idotheinae (Valvifera)
3
0.005
3
2.91
Zoea larvae
1
0.002
1
0.97
Gastropoda
20
19.42
Littoridina comingii
20
0.033
19
18.45
Bivalvia larvae
1
0.002
1
0.97
Insecta
72
69.90
Chironominae (Diptera:Chironomidae)
918
1.505
70
67.96
Hygrobatidae (Acarii)
2
0.003
2
1.94
Trichoptera (Tubo)
2
0.003
2
1.94
Inderminate
4
0.007
3
2.91
Teleostei
CN33 mujeres verano UK2 US4 Confort 4 Plata Plano talón oro Otros sandalias 5 2 PU Las de 5 Casual EU34 Otros 1
5 UK2 Plano Las PU 2 oro Casual sandalias mujeres Confort 4 verano CN33 Otros 5 US4 talón Plata EU34 de Otros Szidat L (1950) Los parásitos del róbalo (
Elegi-
nops maclovinus
Cuv. & Val.).
I Congr.
Nac. Pesquero Marítimo e Ind. Derivadas
.
Mar del Plata, Argentina. pp. 234-270.
Turner A (1988)
Relaciones tróficas de dos es-
pecies
bentófagas,
Cauque
mauleanum
(Steindachner,
1902)
y
Eleginops
maclovinus
(Valenciennes, 1830) (Pisces:
Osteichthyes) en el estuario del río Queule
(IX Región, Chile)
. Tesis. Facultad de
Ciencias, Universidad Austral de Chile.
Valdivia, Chile. 48 pp.
Vila I, Fuentes L, Contreras M (1999) Peces
límnicos de Chile
. Bol. Mus. Nac. Hist. Nat.
Chile 48
: 61-75.
Yamaguti S (1961)
Sistema Helminthum. Vol. III.
The nematods of vertebrates. Part I- II
.
Interscience. New York, USA. 1135 pp.
Motivo:Casual/Género:Mujer,
Categoría:sandalias, y parte superior de los materiales:PU,
Talón talón plano tipo:,
Tenemos fabricantes profesionales, sandalias de estricto control de calidad, buen servicio post-venta
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