Percichthys Trucha Research Articles

Anatomical distribution of scavenger endothelial cells in bony fishes (Osteichthyes)

The scavenger endothelial cells (SECs) of vertebrates are an important class of endocytic cells responsible for clearance of foreign and physiological waste macromolecules, partitioning in the immune system, functioning as a cellular powerplant by producing high energy metabolites like lactate and acetate. All animal phyla possess SECs, but the tissue localization of SECs has only been investigated in a limited number of species. By using a specific ligand for scavenger receptors (formalin treated bovine serum albumin), the study revealed that in all tetrapod species (amphibia, reptiles, birds and mammals) the SECs were found lining the sinusoids of the liver. No SECs were found in the liver of any of the bony fishes (Osteichthyes) investigated. Interestingly, we found the SECs not only to be located in the heart of marine species but also in some freshwater species such as Lota lota, Percichthys trucha and Perca fluviatilis. In some fish species, the SECs were found both in the heart and/or kidney in a number of marine and freshwater fishes, whereas in some marine, diadromous and freshwater fishes the SECs were confined only to the kidney tissue. However, from these results it can be suggested that there is neither a clear phylogenetic trend when it came to anatomical localization of SECs nor any pattern in terms of habitat (salinity preferences).

A regional scale study of parasites in Percichthys trucha, an endemic fish of southern South America: insights on diversity and distribution from two decades of field surveys.

The current conservation status of Percichthys trucha (Creole perch) is Least Concern, although the population trend is considered to be decreasing. We conducted an extensive survey of parasite fauna in this species over two decades in its distribution range in Argentina. Fish were collected using gill and trawl nets. Parasites were collected, identified, and counted to calculate prevalence and mean intensity. The present work reports the parasite species infecting P. trucha, using data from our own survey and from previously published records. This information enables us to evaluate infection and distribution patterns, assess the role of P. trucha as host, determine the specificity of the parasites, and evaluate the threat represented by introduced, invasive parasites. The data set consists of a total of 453 host-parasite-locality records, of which only 15 are exclusively bibliographic. We found 44 parasite taxa: 19 digeneans, 4 monogeneans, 5 cestodes, 8 nematodes, 4 acanthocephalans, 3 crustaceans, and 1 mollusk. The most represented families were Diplostomidae, Heterophyidae, and Dactylogyridae. This study increases the number of parasite species known from 25 to 44. It can be concluded that this parasite fauna is characterized by high diversity, particularly of digeneans, and most of the parasites reproduce within this host, a pattern which is related to the top position of this fish species in the trophic webs. Six parasite species (Allocreadium patagonicum, Homalometron papilliferum, Acanthostomoides apophalliformis, Duplaccessorius andinus, Pseudodelphys limnicola, and Hysterothylacium patagonense) exhibit high host specificity (only matures in Creole perches) and are widely distributed, which could now be considered as "biogeographical core helminth fauna." Some P. trucha populations are affected by the invasion of alien fishes like Cyprinus carpio and pathogenic parasites like Lernaea cyprinacea and Schizocotyle acheilognathi. Our findings emphasize the need for further research.

Hemiuroidean trematodes from freshwater Patagonian fishes: description of a new species, distribution and molecular phylogeny.

A new trematode species, Derogenes lacustris Tsuchida, Flores, Viozzi, Rauque et Urabe n. sp. (Derogenidae: Derogeninae), from freshwater fishes is described using morphological and molecular approaches in Argentinean Patagonia. D. lacustris is the most common hemiuroidean species in the Limay River basin and parasitizes almost all the native and introduced Patagonian freshwater fish. This new species could be considered as the unique freshwater species in the genus Derogenes Nicoll, 1910. Another hemiuroidean species, Thometrema patagonica Szidat (Archiev Hydrobiol 51: 542-577, 1956) Lunaschi et Drago 2000 (Derogenidae: Halipeginae), is found from Percichthys trucha (Perciformes) in the Neuquén River basin. Its diagnosis and molecular data are provided by the present study. In the molecular analysis of the Patagonian hemiuroideans, T. patagonica composes a group with halipeginean species in the phylogenetic tree of 28S rDNA sequences, while D. lacustris is not included in the same group. D. lacustris also shows low intraspecific variation in COI sequences regardless of the localities or host species.

The effects of trophic interaction between the Patagonian native Percichthys trucha and the invasive Oncorhynchus mykiss during the juvenile period

Introduced salmonids have invaded almost all Patagonian freshwater environments, and yet the effect they have had on native fish populations is difficult to evaluate due to a lack of data prior to their introduction. In this study we focused on evaluating trophic interactions during the juvenile period of Oncorhynchus mykiss, and the ecologically similar native Percichthys trucha. For this purpose, we evaluated the diet and size range of juveniles of both species in the Caleufu River over one yearly cycle. The functional response (FR: the relationship between prey density and consumption rate) and functional response ratio (FRR = attack rate/handling time) were estimated for each species, in mono-specific and multi-specific trials. Comparison of the diet of these species by season showed high similarity for spring and summer. It was also found that juvenile sizes of these species overlap during early ontogeny. Additionally, both species presented a type II FR in mono-specific trials, with similar functional curves. In multi-specific experiments O. mykiss juveniles were dominant, leading to a reduction in P. trucha food intake. FRR was higher for O. mykiss than for P. trucha in mono-specific experiments, a difference which increased in multi-specific experiments, indicating the high potential ecological impact of O. mykiss. Our results show it is very likely that O. mykiss and native P. trucha compete in lotic environments, O. mykiss being competitively superior, highlighting the potential detrimental effect they may have during the juvenile period, especially in habitats and seasons where food resources are scarce.

Multiple drainage reversal episodes and glacial refugia in a Patagonian fish revealed by sequenced microsatellites.

The rise of the southern Andes and the Quaternary glacial cycles influenced the landscape of Patagonia, affecting the phylogeographic and biogeographic patterns of its flora and fauna. Here, we examine the phylogeography of the freshwater fish, Percichthys trucha, using 53 sequenced microsatellite DNA markers. Fish (n = 835) were collected from 16 river systems (46 locations) spanning the species range on both sides of the Andes. Eleven watersheds drain to the Pacific, five of which are trans-Andean (headwaters east of Andes). The remaining five drainages empty into the Atlantic. Three analytical approaches (neighbour-joining tree, hierarchical AMOVAs, Structure) revealed evidence of historic drainage reversals: fish from four of the five trans-Andean systems (Puelo, Futalaufquen/Yelcho, Baker, Pascua) exhibited greater genetic similarity with Atlantic draining systems than with Pacific systems with headwaters west of Andes. Present-day drainage (Pacific versus Atlantic) explained only 5% of total genetic variance, while ancestral drainage explained nearly 27% of total variance. Thus, the phylogeographic structure of P. trucha is consistent with episodes of drainage reversal in multiple systems and suggests a major role for deglaciation in the genetic and indeed the geographical distribution of P. trucha in Patagonia. The study emphasizes the significant role of historical processes in the current pattern of genetic diversity and differentiation in a fish from a southern temperate region.

Diet of juvenile Percichthys trucha (Teleostei: Percichthyidae) in Northern Patagonia: the importance of the littoral zone

The creole perch, Percichthys trucha is endemic to southern South America. The objective of this work was to identify the food groups of juvenile perch (up to one year old) in its natural environment, the Espejo Chico Lake. A total 99 individuals fromwere caught, measured and weighed, and their condition factor (K) was calculated. In the diet analyses, nine different groups (orders) were found in the stomach contents: Diplostraca, Cyclopoida, Amphipoda, Diptera, Coleoptera, Ephemeroptera, Plecoptera, Hymenoptera and Odonata. Food items showed no correlation with fish size (<29, 30-49, 50-69 and 70-89 mm). Diptera and amphipods inhabiting littoral areas were the main food items of the juveniles. We can suppose that the Creole perch prefer the littoral zone as a nursery; this obviates the need to migrate to the limnetic zone, since the littoral zone provides better food, stable physical habitats and refuge, and a higher concentration of dissolved oxygen than deeper zones, both for macroinvertebrates and perch.

Seasonal and reproductive migrations in the Creole perch Percichthys trucha (Actinopterygii: Percichthydae) promote both intra-lake and inter-lake habitat connectivity

Fil: Fernandez, Maria Valeria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Fish thermal habitat current use and simulation of thermal habitat availability in lakes of the Argentine Patagonian Andes under climate change scenarios RCP 4.5 and RCP 8.5

Habitat use in relation to the thermal habitat availability and food source as a forcing factor on habitat selection and use of Percichthys trucha (Creole perch), Oncorhynchus mykiss (rainbow trout), Salmo trutta (brown trout) and Salvelinus fontinalis (brook trout) were determined as well as future potential thermal habitat availability for these species under climate change scenarios Representative Concentration Pathways 4.5 and 8.5. This study was conducted in three interconnected lakes of Northern Patagonia (Moreno Lake system). Data on fish abundance was obtained through gill netting and hydroacoustics, and thermal profiles and fish thermal habitat suitability index curves were used to identify current species-specific thermal habitat use. Surface air temperatures from the (NEX GDDP) database for RCP scenarios 4.5 and 8.5 were used to model monthly average temperatures of the water column up to the year 2099 for all three lakes, and to determine potential future habitat availability. In addition, data on fish diet were used to determine whether food could act as a forcing factor in current habitat selection. The four species examined do not use all the thermally suitable habitats currently available to them in the three lakes, and higher fish densities are not necessarily constrained to their “fundamental thermal niches” sensu Magnuson et al. (1979), as extensive use is made of less suitable habitats. This is apparently brought about by food availability acting as a major forcing factor in habitat selection and use. Uncertainties related to the multidimensionality inherent to habitat selection and climate change imply that fish resource management in Patagonia will not be feasible through traditional incremental policies and strategic adjustments based on short-term predictions, but will have to become highly opportunistic and adaptive.

Pseudodelphis eleginopsis n. sp. (Nematoda: Guyanemidae), a new tissue-dwelling parasite of the Patagonian blennie Eleginops maclovinus (Cuvier) (Perciformes: Eleginopsidae) in Argentina, with notes on related forms.

Based on light and scanning electron microscopical studies, a new nematode parasite, Pseudodelphis eleginopsis n. sp. (Dracunculoidea: Guyanemidae), is described from tissues behind the gills of the Patagonian blennie Eleginops maclovinus (Cuvier) (Perciformes: Eleginopsidae) off the Atlantic coast (San Matías and San José Gulfs) of Patagonia, Argentina. The new species is mainly characterised by the length of the body (males 10-13 mm, larvigerous females 31-59 mm), the number (14) and arrangement of cephalic papillae, the absence of a buccal capsule, the muscular to glandular oesophagus length ratio (1:3-4) of larvigerous females, the length of the spicules (48-63 µm) and the number (7 pairs) and arrangement of the caudal papillae in the male. Pseudodelphis eleginopsis n. sp. is the first species of this genus described from a marine fish in the Atlantic Ocean and the first known dracunculoid parasitising the fish host belonging to the family Eleginopsidae. As revealed by the examination of very young females of the new species, the female genital tract of Pseudodelphis spp. is monodelphic. The genus Syngnathinema Moravec, Spangenberg & Frasca, 2001 is considered a junior synonym of Pseudodelphis Adamson & Roth, 1990 and, consequently, S. californiense and S. chitwoodi are transferred to Pseudodelphis as P. californiensis (Moravec, Spangenberg & Frasca, 2001) n. comb. and P. chitwoodi (Moravec & Kuchta, 2013) n. comb., respectively. Two dracunculoid species, Pseudodelphis limnicola Brugni & Viozzi, 2006 and the previously established Philonema percichthydis Moravec, Urawa & Coria, 1997, both described from the same freshwater host species, Percichthys trucha (Valenciennes), in the same region (Patagonia), are considered to be identical; therefore, the valid name of this species is Pseudodelphis percichthydis n. comb. and P. limnicola becomes its junior synonym. A key to the species of Pseudodelphis is provided.

The influence of fish bone morphology on aquatic transport: An experimental approach through elements of Creole perch (Percichthyidae: Percichthys trucha; [Valenciennes, 1833

Many archaeological sites with fish remains are situated near ancient or current water courses. The origin of these time-averaged contexts requires an analysis considering possible non-human contributions and specifically the role of water as a highly selective agent. Element shape is a critical factor in all transport processes, but it has received little attention. The aim of this experimental work is to explore the hydrodynamic transport of fish bones considering the shape of anatomical elements. Different elements from Creole perch (Percichthyidae: Percichthys trucha; [Valenciennes, 1833]) individuals are utilized in dry conditions and under three different flow speeds. Transport groups, mode of transport and distance travelled are evaluated according to the shape of the elements. Fish vertebrae have the greatest transport potential. This experimental study indicates that hydrologic processes can impose biases giving a unique skeletal element composition in fish bone assemblages. A simplified differential transport model is proposed and an archaeological application of it is essayed.

Native and exotic fishes in a Patagonian reservoir with rainbow trout cage culture: spatial and trophic resource use

Although the interactions of exotic salmonids with native Patagonian fishes are well known, little is known about the ecology and impact of farmed fish escapees. Salmonid production in Argentina is largely concentrated in the Alicura reservoir in north Patagonia, where fish community studies have been scarce. Here, we assess and compare the spatial distribution, body size–condition and diet of the different fish species in this reservoir. Strong vertical segregation was observed between exotic rainbow trout Oncorhynchus mykiss (both escapees and wild), dominating the littoral zone, and native Percichthys trucha which dominate the medium and deep strata. Low piscivory–benthivory and high zooplanktivory were observed for rainbow trout, both traits being uncommon at a regional scale. Escaped farmed rainbow trout (ERT) diet included abundant indigestible items along with wild prey. Higher body condition of P. trucha close to farms, as well as the regionally unprecedented high incidence of Daphnia sp. in the guts of all the species suggest that farm nutrient discharges have had significant impacts. Finally, the high body condition of ERT, together with their wild food diet and the long dispersal distance observed, demonstrate post-escape success, drawing our attention to potential upstream dispersion affecting the biodiversity and fisheries of Patagonian rivers and lakes.

The effects of invasive rainbow trout on habitat use and diel locomotor activity in the South American Creole perch: an experimental approach

The effects of the introduced rainbow trout (Oncorhynchus mykiss) on both habitat use and diel locomotor activity of the native Creole perch (Percichthys trucha) were assessed. Experiments were performed with juveniles of both species during a 24-h period. Habitat use was measured in channels with different habitat categories, and diel locomotor activity was registered with an infrared sensor. Both species used mainly cobbles. In the absence of O. mykiss, P. trucha used macrophytes and gravel secondarily, during dusk and midnight, respectively. Oncorhynchus mykiss used gravel and macrophytes secondarily, during midday. In the presence of O. mykiss, P. trucha increased its use of macrophytes and decreased its use of less structured habitats. Percichthys trucha juveniles were more active during night. This pattern did not change in the presence of O. mykiss, nor was the intensity of movement affected. These results reveal the importance of structured environments for juveniles of both species. In particular, substrates of large size with interstitial spaces in between serve as shelter and reduce visual detection between individuals. Both the association of P. trucha juveniles with structured habitats and their nocturnal activity reduce predation risk.

The cephalic lateral line system of temperate perches (Perciformes: Percichthyidae) from Argentinean Patagonia

ABSTRACT The species of Percichthys (Percichthyidae) are endemic to southern South America. Some authors have pointed out that the genus includes four valid species, based on the morphology of the head, jaws, and fins. A phylogenetic analysis published by other authors suggests that three of them are morphotypes belonging to the same species, Percichthys trucha (Valenciennes, 1833). The aim of this study is to describe for the first time the morphology of the cephalic seismosensory system of Patagonian perches, and how these characters vary in the three morphotypes, in order to provide morphological elements to analyze the taxonomy of these fish species. Comparisons of the cephalic seismosensory system between juveniles and adults were also conducted. Juvenile and adult specimens were collected in the northwestern Argentinean Patagonia. Specimens were bleached in 5% H2O2 and the canal systems of their cephalic lateral line were filled with hematoxylin. Specimens were deposited in the Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Argentina. The cephalic lateral line of the studied specimens is a widened type of canal systems, is not connected to the trunk lateral line, and consists of preopercular-mandibular canal, infraorbital canal, supraorbital canal, temporal canal, supratemporal canal, and a supraorbital commisure. The number of pores increases during the ontogeny, while their diameters decrease. The number, position and size of infraorbital canal pores showed significant differences among morphotypes and juveniles. The interpopulation variation regarding the number, position, and size of pores seems to signal an ongoing process of speciation, which is the result adaptations to different environmental conditions. Our study contributes to the knowledge of the morphology of percichthids and describes for the first time the seismosensory system of temperate perches.

Trophic scaling of Percichthys trucha (Percichthyidae) in monospecific and multispecific lakes in western Patagonia

Percichthys trucha is a freshwater fish, endemic to southern South America and widely distributed in both, eastern and western sides of the Andes. P. trucha has been described as top native predator in lacustrine ecosystems, experimenting diet shifting during their life history development. Salmonid invasions have impacted their natural ecology through trophic niche interference and predation over alternative high quality prey. This study focuses on populations of P. trucha in western Patagonia, where its trophic ecology have been less understood. We hypothesised a diet shift between juveniles and adults from lower-trophic position prey towards higher-trophic position prey. Fish were collected from 7 lakes belonging to Puelo and Baker river basins, covering a high diversity of environmental conditions. Stomach content and δ 15 N stable isotope ratio of muscle tissues of 313 individuals were analysed. Results indicate significant differences in diet between juveniles and adults, shifting from planktonic/benthic preys towards benthic/piscivory, and concomitantly enrichment in heavier nitrogen isotope suggest trophic scaling. No trophic scaling was observed in populations inhabiting lakes with any other fish species present, essentially due to lack of Galaxias sp. as available prey and absence of cannibalism. Despite the fact that P. trucha and Galaxias sp. co-occur in studied river basins, no salmonid-free lakes harbouring this two native species were found, making it difficult to elucidate exact effects of salmonids on trophic scaling of P. trucha . Consumption of aquatic Odonata nymphs, however, arises as one of potential key mechanism for resilience of native food webs to salmonid invasion.

Susceptibility of native perca (Percichthys trucha) and exotic rainbow trout (Oncorhynchus mykiss) to high temperature in Patagonia: different physiological traits and distinctive responses

The aim of this work was to explore for the existence of a physiological basis for the apparent exclusion of salmonid fish from the littoral zone of lakes in Patagonia in response to increasing water temperature, to the benefit of the native perca (Perc- ichthys trucha). We conducted experiments on the thermal preferences of juvenile perca and rainbow trout collected in three sites of Northern Patagonia. We characterized the relationship between preferred and acclimation temperature (PT, AT) for perca and trout and analyzed between-sites variations in PTs. Both species responded with increasing PT to higher AT, but with differences in overall PT for perca from different sites (lower PTs for fish from cooler lake). In general, rainbow trout displayed lower PT and a narrower range of PT than perca. Our results provide the first comparative view of PTs of one important native fish and the main sport fish species of Patagonia. Native perca may be better equipped to cope with warmer waters than exotic rainbow trout, in agreement with their geographic distribution. Also, perca may have an advantage at the local level, particularly in littoral areas of lakes, through the alleviation of predation by and trophic competition with trout.

Modeling Prey Consumption by Native and Nonnative Piscivorous Fishes: Implications for Competition and Impacts on Shared Prey in an Ultraoligotrophic Lake in Patagonia

AbstractWe examined trophic interactions of the nonnative salmonids Rainbow Trout Oncorhynchus mykiss, Brown Trout Salmo trutta, and Brook Trout Salvelinus fontinalisand the main native predator Creole Perch Percichthys trucha in Lake Nahuel Huapi (Patagonia, Argentina) to determine the relative impact of each predator on their forage base and to evaluate the potential vulnerability of each predator to competitive impacts by the others. Using bioenergetics simulations, we demonstrated the overall importance of galaxiids and decapods to the energy budgets of nonnative salmonids and Creole Perch. Introduced salmonids, especially Rainbow Trout, exerted considerably heavier predatory demands on shared resources than did the native Creole Perch on both a per capita basis and in terms of relative population impacts. Rainbow Trout consumed higher quantities and a wider size range of Small Puyen (also known as Inanga) Galaxias maculatus than the other predators, including early pelagic life stages of that prey; as such, this represents an additional source of mortality for the vulnerable early life stages of Small Puyen before and during their transition from pelagic to benthic habitats. All predators were generally feeding at high feeding rates (above 40% of their maximum physiological rates), suggesting that competition for prey does not currently limit either Creole Perch or the salmonids in this lake. This study highlights the importance of keystone prey for the coexistence of native species with nonnative top predators. It provides new quantitative and qualitative evidence of the high predation pressure exerted on Small Puyen, the keystone prey species, during the larval to juvenile transition from pelagic to littoral‐benthic habitat in Patagonian lakes. This study also emphasizes the importance of monitoring salmonid and Creole Perch population dynamics in order to detect signs of potential impacts through competition and shows the need to carefully consider the rationale behind any additional trout stocking.

Selenium Species and Their Distribution in Freshwater Fish from Argentina

The distribution and speciation of selenium (Se) in freshwater fish (muscle and liver tissue) from lakes in Argentina was investigated. Three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), and one native species, creole perch (Percichthys trucha), were investigated. Values for total selenium in muscle ranged from 0.66 to 1.61 μg/g, while in the liver, concentrations were much higher, from 4.46 to 73.71 μg/g on a dry matter basis. Separation of soluble Se species (SeCys(2), selenomethionine (SeMet), SeMeSeCys, selenite and selenate) was achieved by ion exchange chromatography and detection was performed by inductively coupled plasma-mass spectrometry. The results showed that in fish muscle, from 47 to 55 % of selenium was soluble and the only Se species identified was SeMet, which represented around 80 % of soluble Se, while in the liver, the amount of soluble Se ranged from 61 to 76 % and the percentage of species identified (SeMet and SeCys(2)) was much lower and ranged from 8 to 17 % of soluble Se.

Diet of Breeding Neotropic Cormorants at the Carrileufu River, Patagonia: Is there Any Impact on Recreational Fish Resources?

Summary. Some cormorant species are perceived as negatively interacting with fish resources but conclusive evidence supporting such suggestions are scarce. Here we studied the diet of the neotropic cormorant and assessed its impact on recreational fish resources. A total of 33 pellets (regurgitated casts) and 73 regurgitations produced by the Neotropic cormorant were collected between 19 October 2006 and 24 February 2007 at a colony on the Carrileufu River, Patagonia, Argentina. Fish (94.3%) were the most abundant prey, followed by crustaceans (5.1%) and molluscs (0.6%). The Patagonian silverside Odontesthes hatcheri was the most frequent fish prey, followed by the rainbow trout Oncorhynchus mykiss and the creole perch Percichthys trucha. The contribution of fish species to the diet varied throughout the breeding season. The fish intake estimate for the colony based on parameters drawn from previous studies was 4.708 tons, which represents a consumption of 41,504 fish specimens. Native species were the ma...

The importance of substrate size and interstitial space in the microhabitat selection by the stream-dwelling catfish Hatcheria macraei (Actinopterygii, Trichomycteridae)

The study tests whether diurnal microhabitat use by Hatcheria macraei depends upon specific environmental parameters and/or the abundance of other fish. We carried out a 1-year field study in a low-order river of northern Patagonia, Pichileufu River, and used experimental trials to determine substrate preferences. Fishes were captured during daylight and physicochemical environmental variables were recorded. Headwater zones were dominated by rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta), while native fishes, H. macraei and the creole perch (Percichthys trucha) were more abundant downstream. H. macraei inhabited mostly shallow microhabitats with fast water velocity and substrates having significant interstitial spaces, independently of the abundance of other fishes. Experimental trials pointed out that H. macraei preferred mostly coarser substrates (>6 cm), avoiding fine ones. This study highlights the importance of erosional zones with high water velocity, large substrates, and suitable interstitial space in the microhabitat selection of H. macraei. The knowledge of microhabitat use by native fish populations is critical for management and conservation strategies and should be taken into account before any river modification.

Food web structure in a double-basin ultra-oligotrophic lake in Northwest Patagonia, Argentina, using carbon and nitrogen stable isotopes

Fish, benthic macroinvertebrates, macrophytes, biofilm, plankton, and terrestrial material were analyzed for stable nitrogen (δ15N) and carbon isotopes (δ13C) to study the food web structure of a double-basined, ultra-oligotrophic lake in northwest Patagonia. The δ15N values of all biota were consistently higher in Moreno East basin, probably caused by a higher anthropogenic impact; however, the estimated trophic positions of fish showed no differences between basins, indicating that fish are feeding from food chains with different δ15N baselines. Fish δ13C values were higher in Moreno West basin but no pattern was observed for the rest of the organisms analyzed. The different hydrogeomorphic characteristics between the basins could lead to these differences in the C signatures of fish. SIAR (Stable Isotope Analysis in R) mixing model was used to study possible food sources for adult fish and the results were contrasted with published gut content analysis. According to the model, in both basins small size fish such as Small Puyen (Galaxias maculatus) and juvenile fish, had the highest relative isotopic contribution to introduced Rainbow Trout (Oncorhynchus mykiss) and Brook Trout (Salvelinus fontinalis), which had lower contributions from other sources such as insect larvae, decapods, and snails. On the contrary, decapods and insect larvae were isotopically more important for the native Creole Perch (Percichthys trucha) than small fish in both basins. An ontogenetic shift in the carbon source and trophic level was observed in Puyen Chico and Rainbow Trout from the West basin.