Confort De CN39 Otoño Mujeres Oficina US8 Casual Pu De Ons RTRY Carrera Traje Noche amp;Amp; UK6 Soles Lace Uplow Luz Bowknot amp;Amp; amp;Amp; Parte EU39 Mocasines De Slip Boda Primavera w1Yq7

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120
MAR 2005, VOL. 30 Nº 3
Keywords: /
Eleginops /
Eleginopidae / Feeding Shifts / Osmoregulation / South America /
Mujeres Parte Lace De Noche Confort Traje Carrera De Otoño Pu Mocasines Uplow Bowknot Ons Slip Soles US8 EU39 RTRY Boda De amp;Amp; UK6 amp;Amp; Luz Primavera amp;Amp; CN39 Casual Oficina 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
amp;Amp; Primavera EU39 Mujeres amp;Amp; amp;Amp; Uplow Luz UK6 Pu Ons Soles Confort Oficina Parte RTRY Slip De Carrera Boda Casual US8 Noche Lace De Bowknot Traje CN39 Otoño Mocasines De 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
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0.97
Inderminate
1
0.002
1
0.97
Bryozoa
81
78.64
Indet. ovoid structures
519
0.851
57
55.34
Filaments
44
42.72
Plants
48
46.60
Scirpus californicus
(Cyperaceae)*
139
0.228
29
28.16
Inderminate
46
44.66
TOTAL
60985
103
* Seeds
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Figure 1. Geographic location of sampling stations, within the estuarine system of the
Valdivia River, Chile. a: Las Mulatas, b: Los Pelúes.
122
MAR 2005, VOL. 30 Nº 3
stomachs (F%) were the crustaceans
(93.2%), followed by ramose bryozoans
(78.64%), insects (69.9%), lake plants
(46.6%), gastropods (19.42%) and, fi-
nally, a bony fish (0.97%, Table I). In
relation to the number of individuals per
group (N%) the class Crustacea repre-
sented 97%, followed by Insecta (1.5%)
and bryozoans, lake plants, gastropods
and Teleostei, each at proportions below
1% (Table I). A grand total of 98.9%
(N, N%) of the items recorded in the
stomachs were of animal origin, with
less than 1.1% of plant origin.
Taxonomic analysis of the stomach
contents by systematic group
Statistically
significant
differences were observed among the
abundances (N) of the different food
items analyzed (Kruskal-Wallis test:
H(15, N=1599)= 949.94 p<0.01).
The taxa showing the
statistically greatest abundances were 1)
the corophiid amphipods (mostly
Para-
corophium hartmannorum
), 2) Diptera:
Chironomidae, 3) bryozoans, and 4) lake
plants (Multiple Comparison Kruskal-
Wallis test, p<0.01). Each of the preced-
ing groups demonstrated absolute, el-
evated abundances, and distinct tenden-
cies among themselves (Table I).
1) Class Crustacea: In this group the
main taxon in numerical abundance
(N%) as well as in frequency of occur-
rence in stomachs (F%) was shown by
the lacustrine amphipod
Paracorophium
hartmannorum
,
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represented
97% of the individual prey species,
and was found in 93.2% of the stom-
achs analyzed (Table I). Other crusta-
cean items included Tanaidacea (Ma-
lacostraca), Ciprinidae (Ostracoda),
Hemigrapsus crenulatus
(Decapoda),
and Idotheinae (Isopoda, Valvifera)
which as a group represented less than
1% of the total individuals counted.
The tanaids, ciprinids, and
H. crenu-
latus
gave frequencies of occurrence of
between 2.9 and 13.5%. Finally, a bra-
chyuran zoea larva was encountered,
representing less than 1% both in abun-
dance and frequency.
2) Class Mollusca: Only one species of
gastropod,
Littorina cumingii
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, was re-
corded, which had a frequency of occur-
rence of near 18.4%, and an abundance
of less than 1%. A few bivalve veliger
larvae were also observed.
3) Class Insecta: The most important
taxon of this group were Diptera of the
family Chironomidae, with an abundance
of 1.5%, and a frequency of occurrence
of 67.9%, making it the second most
common item eaten by the fish. Also
identified were trichopteran tubes and a
hygrobatid mite, representing less than
1% in abundance and 1.9% in frequency
of occurrence.
4) Subdivision Teleostei: Only one indi-
vidual was recorded, and this was in an
advanced stage of digestion, remaining
unidentified. This represented less than
1% in frequency of occurrence and
abundance among the items analyzed.
5) Ramose invertebrates: Due to their
advanced state of digestion, specific
identification of this material was im-
possible, although its tubular structure,
dichotomous ramification and presence
of ovoidal structures in the external
walls suggested it to be assigned to
“bryozoa”. These remains were found in
78.64% of the stomachs, but with an
abundance near 1%. Quantification of
this material was difficult due to clump-
ing, but undoubtedly represented a fre-
quent item in the stomachs of
E.
maclovinus
.
6) Lacustrine plants: 46.6% of the
stomachs contained remains of lake
plants, including both vegetal portions
and seeds: the latter were determined
to be seeds of
Scirpus californicus
(Cyperaceae) and had a frequency of oc-
currence of 28.1% and an abundance of
less than 1% (Table I; Ramírez
et al
.,
1976).
7) Nematode parasites (Table II): The
main nematode parasite in the stomachs
of the fish was
Primavera UK6 Mujeres amp;Amp; Luz RTRY US8 Parte Noche Casual Uplow Oficina Pu Mocasines Confort Traje Boda Bowknot CN39 amp;Amp; Soles Lace Otoño Ons amp;Amp; EU39 De De De Carrera Slip Ascarophis
sp. (Cystido-
colidae), with both mature males and fe-
males present. This nematode had a fre-
quency of 44.6% and an abundance of
75.7% (n= 87), and was the most nu-
merous of the helminths identified. Also
identified from the stomachs were ma-
TABLE II
FREQUENCY OF OCURRENCE (F, F%) AND NUMBER OF PARASITE
NEMATODS (N, N%) IDENTIFIED WITHIN THE STOMACH CONTENTS
OF
Eleginops maclovinus
IN THE VALDIVIA RIVER
Parasites
N
N(%)
F
F (%)
Ascarophis
spp. (Cystidicolidae)
87
75.7
46
68.7
Anisakids
28
24.3
21
31.3
Total
115
100
67
100
Figure 2. Variation in the stomach contents of
Eleginops maclovinus
. a: common items,
b: less common items (lower occurrence and presence).
MAR 2005, VOL. 30 Nº 3
123
ture anisakids, at a frequency of 20.3%.
This group included 15 larvae and 13
adults.
Analysis by size of fish
When the fish samples
were separated into size ranges of 1cm,
to give 13 ranges between 15 and 30cm
TL, no statistically significant differences
were observed in total species abundance
in stomachs from the different size
groups (Kruskal-Wallis test H(12, N=
1599)= 19.21559, p>0.05). However, a
decrease in abundance of the Coro-
phiidae, lacustrine plants (
S. californicus
),
bryozoan remains, Chironomidae, and Os-
tracoda was observed as total length of
the fishes increased (Figures 2a, b). In
contrast, the Idotheidae,
H. crenulatus
,
one teleost, and
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L. cumingii
were re-
corded in specimens over 19cm SL, and
increasing in the larger
E. maclovinus
(Figure 2b).
With the nematode para-
sites, greater numbers of anisakids were
found in the smaller fish specimens, con-
trary to the numbers of ascarophites
which were more common in the larger
fishes.
Comparison of the fish stomach
contents and river fauna
Items found in the
E.
maclovinus
stomachs were common at
both stations sampled in the Valdivia
River,
including
P.
hartmannorum
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Chironomidae, and Trichoptera. (Tables
II, III). There was, however, variation in
abundance and diversity of the four taxa
in relation to the sampling depth in the
river (shore
vs
. depth). Amphipods were
more abundant in shore samples at Las
Mulatas. In mid-river, the polychaetes
Prionospio
sp. and
P. gualpensis
were
more abundant, although they were not
recovered from the stomach contents of
the fish. Lower abundance and biomass
were found at Los Pelúes than at Las
Mulatas, where the oligochaete
Tubifex
sp. inhabited anoxic bottoms rich in or-
ganic matter. This species was not re-
covered from fish stomachs. Thus, some
of the potential preys are not used by
the fishes.
Discussion
Among the large variety
of food items present in the stomach
contents of
E. maclovinus
we found re-
mains of algae, land plants, crustaceans,
insects, mollusks and fishes.
The item with the high-
est frequency of occurrence was
Para-
corophium
hartmannorum
,
somewhat
similar to that recorded by Pequeño
(1979). It should be noted that Pequeño
(1979) considered specimens between
280 and 880mm TL, to be inhabitants of
marine or mixohaline habitats. In the
present study samples obtained were be-
tween 180 and 400mm TL, and distrib-
uted in areas of strong limnetic affinity
and low salinity (Valdivia River surface
salinity= 0‰, bottom salinity= 5‰;
Wladimir Steffen, personal communica-
tion).
The Las Mulatas station
is at the limit of effect of the estuarine
salt wedge in the Valdivia River estuary,
with freshwater occurring to the head of
the estuary, and tidal motion noted up to
20km inland from the mouth of the estu-
ary (Pers. Comm. Wladimir Steffen).
The
majority
of
samples
of
E.
maclovinus
having stomach contents
CN39 Bowknot Uplow Carrera amp;Amp; Pu Parte Mujeres Mocasines Lace Ons Confort Luz Primavera amp;Amp; EU39 UK6 De Otoño US8 Casual Slip Traje Oficina Boda Noche RTRY De De amp;Amp; Soles (93%), the low degree of digestion of
the prey, and the similarities between
species ingested and those recorded
from the environment, allow the assump-
tion that Las Mulatas is a feeding area
used by the fishes to exploit resources
located near the rivers edge (Table I,
III).
Various species of poly-
chaetes, including
Perinereis gualpensis
and
Prionospio
sp
.
were found in the
sediment, but not among the stomach
contents although other investigators re-
corded the presence of polychaete re-
mains as well as remains of the oli-
gochaete
Tubifex
sp. (Ruiz, 1993). This
situation may be explained by the life
style of these annelids (buried, as
endofauna), and with soft body struc-
tures which are easily digested, imped-
ing their identification in the stomachs.
Another possibility is that they may be
negatively selected by the fish, based on
its feeding behavior which includes
grazing over sand or gravel, not appear-
ing to consume species which are in
lime-clay sediments containing decom-
posing organic material as typical of
Prionospio
sp. and
P. gualpensis
. This
situation would reflect a selective behav-
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and sandy areas, or in association with
small filamentous algae where benthic
grazing behavior is possible (
eg
. Tri-
choptera, Chironomidae, and
P. hartman-
norum
). The fish may be an opportunis-
tic predator (Morin, 1999) since it ex-
ploits the resource in major abundance
in the environment (
eg. P. hartman-
norum
).
The remains assigned to
bryozoa and lacustrine plants observed
in the stomach contents of
E. maclovinus
probably represent items accidentally
consumed during feeding on crustaceans
and/or insects due to the common be-
havior arthropods such as the amphi-
pods, isopods and insects in seeking ref-
uge in filamentous microhabitats such as
algae and other plants, reducing predator
pressure and indirectly increasing the
food offering of the substrate (Schneider
and Mann 1991a, b; Peñaloza, 1993).
Another aspect suggesting the accidental
nature of consumption of the bryozoans
was the low degree of digestion of this
material in the fish stomachs. The same
occurred for
Scirpus
californicus
, where
accidental ingestion of the seeds may be
related to sedimentary grazing on animal
prey, particularly the chironomids. The
accidental consumption of seeds may
lead to probable “ichthyochoria” or seed
dispersal by fishes as found in the Ama-
zon by Gottsberger (1978). This was
also noted by Guzmán and Campodónico
TABLE III
ABUNDANCE AND BIOMASS OF MACROBENTHOS SPECIES IN SECTORS*
OF LOS PELÚES AND LAS MULATAS AT THE VALDIVIA RIVER
Los Pelúes margin
Los Pelúes center
Taxa
Abundance /
Biomass
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Biomass
m
2
(gr/m
2
)m
2
(gr/m
2
)
Prionospio
sp.
63.14
0.006
357.77
0.08
Perinereis gualpensis
168.36
0.59
631.36
1.30
Paracorophium hartmanorum
841.81
0.07
2209.75
0.27
Tubifex
sp.
168.36
0.010
21.04
0.002
Las Mulatas margin
Las Mulatas center
Prionospio
sp.
105.23
0.019
3556.65
0.85
Perinereis gualpensis
526.13
0.73
1452.12
1.85
Paracorophium hartmanorum
2336.02
0.24
589.27
0.06
Trichoptera
21.04
0.09
0
0
Chironomidae
21.04
0.006
0
0
* The sectors are differentiated according to sampling locations, margin or center.
124
MAR 2005, VOL. 30 Nº 3
(1973) who reported seeds of graminea
in
E. maclovinus
stomach contents.
The
crustaceans,
in-
sects, and plants observed in the stom-
ach contents in this study, have only
been reported from limnetic or estua-
rine environments (see Stuardo, 1961;
Ramírez
et al
., 1976; Pequeño, 1979;
Artigas
et al
., 1985; Jaramillo
et al
.,
1985; Bertrán, 1989; Ruiz, 1993). This
suggested that the fishes sampled had
not migrated into brackish (Corral Bay,
9.2‰ surface, 33.7‰ bottom salinity)
or marine areas to feed, but rather con-
sumed prey from freshwater, upper
reaches of the river (0‰). This capacity
for tolerating low salinity and feeding
on limnetic species explains catches of
these fishes to more than 21km inland
from the mouth of the Valdivia River.
This aspect is corroborated by the lim-
netic fish fauna associated with the ar-
eas from which present samples were
obtained, such as
Austromenidia laticla-
via, Basilichthys australis, Oncorhyn-
chus mykiss, Mugil cephalus, Galaxias
maculatus, G. platei, Cheirodon
sp.
(Ruiz, 1993; Vila
et al.
, 1999). Of these
only
M. cephalus
is capable of life both
in the sea and in freshwater (Ruiz,
1993).
It has been recognized
that freshwater fishes have a diet simi-
lar to that of
E. maclovinus
in this
study in these habitats. Thus
Oncorhyn-
chus mykiss
and
Cauque mauleanum
feed principally on chironomid larvae
and pupae, Littorinidae, Trichopteridae,
Acarii, and Amphipoda (Artigas
et al.
,
1985; Klink and Eckmann, 1985).
The data showing that
as the fishes grew in size and weight,
corophiid
crustaceans
(
P.
hartman-
norum
) significantly decreased in the
stomach contents, as also found with
the ostracods, suggested a succession of
species taken by
E. maclovinus
with in-
crease in size, where smaller prey items
are progressively replaced by larger
ones. In spite of these changes in pre-
dation, the fish was observed to be
more of a carnivore than herbivore, in
agreement with Pequeño (1979), Turner
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(1988), Acevedo (1994), and Isla and
San Román (1995) and differing from
the hypothesis of Guzmán and Cam-
podónico (1973). Pequeño (1979) and
Parte RTRY De Mocasines UK6 Noche US8 Otoño De Soles Casual De EU39 Mujeres Traje Luz Carrera amp;Amp; Oficina Slip amp;Amp; Pu Uplow Confort Boda Lace CN39 Primavera Bowknot amp;Amp; Ons Acevedo (1994) recorded that in indi-
viduals of 240-280mm TL from marine
and mixohaline environments 84% of
the food items were of animal origin
(e.g. crustaceans, chordates) and over
11% of plant origin, increasing in the
present study to 98.9% animal, and
>1% plant remains. Algal remains cited
by Pequeño (1979) and Acevedo (1994)
and other studies included
Enteromor-
pha, Porphyra
, and
Ulva
which are spe-
cies which typically harbor crustaceans
and show little sign of digestion in the
digestive tract of the fishes, which
makes it doubtful that they serve as an
energy source (Isla and San Román,
1995). However, it is difficult to say at
what point microscopic algae, generally
present in the surface of other organ-
isms, may play a role in fish nutrition.
Pequeño (1979), Aceve-
do (1994), Ruiz (1993) and Isla and
San Román (1995) determined that
E.
maclovinus
Carrera UK6 US8 RTRY Boda Mocasines De Noche Uplow Otoño CN39 EU39 Primavera Mujeres Casual De Oficina Slip amp;Amp; Traje Parte Pu De amp;Amp; Lace Soles Bowknot Confort Ons Luz amp;Amp; was predominantly feeding
on crustaceans, since amphipods, iso-
pods, cumaceans, and decapods were
the most abundant prey found in indi-
viduals from 61 to 240mm TL and
from 180 to 700mm TL.
Although the results of
the present study concur with those of
Guzmán and Campodónico (1973) in
relation to the predominance of car-
nivorous feeding in
E. maclovinus
Confort Carrera Oficina Mocasines CN39 Slip amp;Amp; Bowknot Traje UK6 Otoño Mujeres Ons Parte De Soles RTRY Pu Lace De Primavera Luz Uplow Casual Boda amp;Amp; De amp;Amp; US8 EU39 Noche ,
those authors maintained that individu-
als of this species greater than 160mm
SL were basically herbivorous. They
mentioned that individuals from 160 to
410mm SL fed predominantly on algae,
which had a frequency of occurrence of
94% and occupied approximately 83.4%
of the volume of the stomachs.
The present study, al-
though showing a frequency of occur-
rence of plant material of 86.7%,
showed an abundance of significantly
less than 1% which was markedly dif-
ferent than that observed by Guzmán
and Campodónico (1973). This sug-
gested carnivorous behavior in the size
classes studied from the Valdivia River,
which may be a tendency maintained
over time in accordance with the stabil-
ity of food resources (Acevedo, 1994).
Gosztonyi (1979), simi-
larly to Guzmán and Campodónico
(1973) suggested that the
E. maclovinus
studied was an omnivorous species with
clear tendencies towards consumption
of plant material in all stages of its de-
velopment. However, he did not present
evidence for digestion of the plant ma-
terial placing doubts on its value as an
energetic input. Gosztonyi's (1979) ob-
Noche De CN39 amp;Amp; US8 Casual Traje De Mocasines amp;Amp; Carrera Oficina RTRY Parte Lace Soles Mujeres Ons De Confort UK6 EU39 Otoño Uplow Boda Luz Primavera Bowknot Pu amp;Amp; Slip servations have also been noted by
other authors. According to him fila-
mentous structures such as the form of
some bryozoans, provide refuge for
crustaceans, and as presently suggested
there is no evidence that the fish is a
primary consumer.
In addition to previous
studies concerning the broad scope of
feeding of
E. maclovinus
(Pequeño,
1979; Turner, 1988; Acevedo, 1994),
the present study shows its capacity to
feed in limnetic habitats as part of its
capacity for survival in freshwater. The
reduced number of species found in the
fish stomachs in the limnetic habitat
(14 items, present study) is a reflection
of the reduced species diversity of the
freshwater habitat compared with those
of the estuary (Beagle Channel, 24
items; Isla and San Román, 1995) and
marine habitats (Mehuín, 35 items;
Pequeño, 1979). This aspect is related
to the selectivity of the predator and
lower diversity of prey in inner beaches
of the estuary compared with the mouth
of the estuary of the Valdivia River
(Low, 1993; García and Ojeda, 1995),
together with the general tendency to-
wards lower species diversity in estuar-
ies than in seas or lakes (Kiely, 1999).
It was of interest that
mature nematodes of the genus
Ascaro-
phis
occurred in
E. maclovinus
, since
this fish had not been considered as a
definitive host for this nematode (Muñoz
and George-Nascimento, 2002). Our
records indicate that infection by these
parasites (anisakids and
Ascarophis
sp.)
occurred in
E. maclovinus
at sizes less
than 150mm SL, both in limnetic and
estuarine systems. This point was not
mentioned in the review of Marcogliese
(2002) although reported by Muñoz and
George-Nascimento (2002).
Another parasite,
Cys-
tidicola
sp. (fam. Thelaziidae), was
identified from
E. maclovinus
stomachs
by Szidat (1950). This parasite is only
known from freshwater habitats where
it infects intermediate and definitive
hosts, in contrast to
Ascarophis
sp.
which are found in hosts in both estua-
rine and limnetic habitats (Ronald,
1986). Identification of
Cystidicola
sp.
in this study demonstrates that these
fishes were feeding on freshwater crus-
taceans.
Marcogliese
(2002)
suggested that the definitive host for
this species could be fishes, birds, or
mammals, with the intermediate hosts
being mainly crustaceans, particularly
decapods of the genera
Pagurus
or
Carcinus
. Fagerholm and Butterworth
(1988) previously indicated that both
larvae and some adult stages of
Ascarophis
sp. were isolated from deca-
pods, isopods, and mainly amphipods of
18-20mm in TL in marine and estuarine
environments. The preceding two re-
ports suggest that the intermediate hosts
of
Ascarophis
sp. in the Valdivia River
may be
Hemigrapsus crenulatus
or
Paracorophium
hartmannorum
based on
their high frequency of occurrence in
the fish stomach contents, which merits
MAR 2005, VOL. 30 Nº 3
125
future study. The preceding
indirectly
confirms our observations on the occur-
rence of carnivorous feeding in
Ele-
ginops maclovinus
in the Valdivia River.
Marcogliese
(2002)
suggested
that
Ascarophis
sp. (Cystidicolidae) had
gadiform fishes as definitive hosts, and
this type of result should be tested in
E. maclovinus
because it is a perciform
fish
(Eleginopsidae:
Notothenioidae,
this study; Muñoz and George-Nasci-
Lace De EU39 Carrera Slip Soles Ons US8 amp;Amp; RTRY Luz Pu Primavera UK6 Bowknot Oficina Mujeres Uplow amp;Amp; Casual Boda Noche De Traje Parte Otoño Mocasines Confort CN39 De amp;Amp; mento, 2002). The parasitological re-
search needs to be broadened by ex-
tending the range of the area consid-
ered and using larger sample numbers
and a broad range of sizes, as well as
extending the parasitological analyses
and obtaining more information on the
food species availability. All this with
the object of better understanding the
ontogenetic variation and trophic behav-
ior of
E. maclovinus
within a referen-
tial framework which may provide new
light on the biological and phylogenetic
EU39 Traje Pu Mocasines RTRY US8 Lace De Confort Parte CN39 De Boda Oficina Noche amp;Amp; Slip UK6 Luz amp;Amp; Bowknot Ons Soles Mujeres De Otoño Carrera amp;Amp; Casual Primavera Uplow history of the suborder Notothenoidei.
The present results sup-
port our initial hypothetical idea, stated
in the Introduction, that
E. maclovinus
living in fresh waters has to eat fresh-
water organisms, despite the fact that
the species is well known as a marine
fish. The present study also opens pos-
sibilities to the hypothesis that this spe-
cies lives in freshwater for extended pe-
riods of time, without needing marine
salinity for survival. This behavior, to
some extent, contributes to the idea that
this species is probably one of the old-
est living species of notothenioid,
which, due to its Antarctic origin, must
have been initiated by individuals ca-
pable of living in areas with permanent
melting of ice, at very low salinities.
ACKNOWLEDGEMENTS
The
authors
express
their gratitude to León Matamala for
laboratory assistance at the Institute of
Zoology, Universidad Austral de Chile
(UACh). For their assistance in the
identification of specimens, to Carlos
Jara, Maritza Mercado, Alejandro Bravo
and Wladimir Steffen at the Institute of
Zoology; to Jorge Jaramillo, Carlos
Ramírez and Miguel Álvarez at the In-
stitute of Botany; to M. Teresa Gon-
zález and Daniel Ekblaw, Doctoral Pro-
gram in Sciences, all from UACh; and
to M. Eliana Ramírez and Melica
Muñoz Schick, Botany Section, Na-
tional Museum of Natural History,
Santiago, Chile. This study is part of
Project S-200223 of the Division of Re-
Boda De UK6 CN39 Pu Noche Luz Parte US8 Ons Oficina De Casual Soles Lace amp;Amp; Mujeres Slip Primavera Bowknot De Confort Carrera Traje Mocasines EU39 Uplow RTRY Otoño amp;Amp; amp;Amp; search and Development, UACh, Val-
divia, Chile.
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