Pablo H. Vigliano

Response of Rainbow Trout to Different Food Web Structures in Northern Patagonia: Implications for Growth, Bioenergetics, and Invasiveness

Abstract Rainbow trout Oncorhynchus mykiss have successfully colonized almost all available water bodies in Patagonia. Introduction and restocking practices have taken place since the beginning of the 20th century without prior consideration of differences between environments in terms of fish community composition and trophic food web structure. We assessed how observed growth, growth efficiency, production, and biomass of rainbow trout populations from four Patagonian lakes were influenced by food web structure and prey quality, and we evaluated the growth strategies adopted by this species in response to environmental differences. Fish communities vary in terms of species composition and dominance. Bioenergetics simulations showed that size and growth patterns of rainbow trout varied between lakes, mainly owing to dietary differences. Fewer and lower-quality food items led to low growth efficiency and stunted growth, while a more diverse and higher-energy diet base led to higher growth efficiency and l...

Selenium and Mercury in Native and Introduced Fish Species of Patagonian Lakes, Argentina

A survey of mercury (Hg) and selenium (Se) contents was performed in fish collected from lakes located in two National Parks of the northern patagonian Andean range. Two native species, catfish (Diplomystes viedmensis) and creole perch (Percichthys trucha), and three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis), were caught from lakes Nahuel Huapi, Moreno, Traful, Espejo Chico, and Guillelmo belonging to Nahuel Huapi National Park and from lakes Futalaufquen and Rivadavia, Los Alerces National Park. In lake Moreno, fish diet items were analyzed and rainbow trout grown in a farm. Hg and Se were measured in muscle and liver tissues by instrumental neutron activation analysis. The average concentrations in muscle of Hg for all species, ages, and lakes are between 0.4 to 1.0xa0μg g−1 dry weight (DW) with a few fish, mainly native, exceeding the United States Environmental Protection Agency health advisory for freshwater fish limited consumption, and from 0.8 to 1.5xa0μg g−1 DW for Se. Average concentrations in liver of Hg in all species range from 0.4 to 0.9xa0μg g−1 DW. Brown trout, the top predator in these lakes, showed the lowest average Hg burden in both tissues. Se concentrations in the liver of brown and rainbow trout, up to 279xa0μg g−1 DW, are higher than those expected for nearly pristine lakes, exceeding 20xa0μg g−1 DW, the threshold concentration associated with Se toxicity. These species show lower Hg contents in muscle, suggesting a possible detoxification of Hg by a Se-rich diet. Creole perch and velvet catfish livers have lower Se concentrations, with a narrower span of values (2.3 to 8.5xa0μg g−1 and 3.3 to 5.5xa0μg g−1 DW respectively).

Niche segregation facilitates coexistence between native and introduced fishes in a deep Patagonian lake

AbstractSpecies introductions force sympatry between species that did not coevolve.n Introduced salmonids have coexisted with native fish since the early 20th century inn Patagonian water bodies, thus generating questions about the mechanisms thatn facilitate their coexistence. We analyzed the trophic and spatial intra- andn inter-specific relationships established among native and salmonid species in a deepn oligotrophic lake of Patagonia in order to determine niche partitioning patterns asn strategies for their coexistence. Salmonids were more generalist feeders, whilen native species had narrower trophic niches. Native fish and introduced salmonidsn partitioned food, mainly through the consumption of the crayfish Samastacus sp. and the native galaxiid Galaxias maculatus, respectively. The diet of mostn species changed with body size, shifting from insects/amphipods to the largern G. maculatus and crayfish. Trophicn interactions varied with season, in association with prey seasonality. In general,n fishes feeding on the same prey were captured in the same depth strata, indicatingn common use of food and space. Our results provide new evidence on the trophicn ecology of a mixed fish community (exotic-native), supporting the idea that nativen and non-native fishes could be avoiding negative interactions (e.g., competition)n through trophic and spatial resource partitioning.

Heavy Metal and Other Trace Elements in Native Mussel Diplodon chilensis from Northern Patagonia Lakes, Argentina

Native mussels, Diplodon chilensis, were sampled from four lakes in Nahuel Huapi National Park, Northern Patagonia, Argentina in order to evaluate heavy-metal distribution in the region and to assess the contribution of this compartment of the trophic web to their circulation in the food chain. The concentration of potential pollutants Ag, As, Cr, Hg, Sb, and Se, and other nine elements of interest (Ba, Br, Ca, Co, Cs, Fe, Na, Sr, and Zn) were determined in Diplodon chilensis pooled samples. Digestive glands were analyzed separately from soft tissues. Geological tracers Sc, Ta, Th, and rare earth elements were also determined in order to discriminate lithophile contributions. Elemental concentrations of Ba, Br, Fe, Sr, Se, and Zn in total soft tissues samples do not show significant differences among sampling sites. Arsenic and Cr contents in total soft tissues and digestive gland pooled samples are higher in sampling points close to zones with human settlements. Silver contents in samples collected in Lake Nahuel Huapi were higher than in the other lakes studied, and up to 50-fold higher than the sample collected in Lake Traful, considered as the reference. Mercury highest concentration values measured in total soft tissues pooled samples from lakes Nahuel Huapi and Moreno were found to be similar to those observed in other reported Hg contamination situations, and they are three to five times higher than those of the reference samples collected in Lake Traful.

Salmonid Introductions in Patagonia: A Mixed Blessing

The fish communities of Argentine Patagonian basins are characterized by low species diversity. Their fish community structure and underlying intra- and interspecific dynamic relationships have been and are still poorly understood. Around 1904, 10 species from Northern Hemisphere hatcheries were introduced for sportfishing. Following the original introductions, unplanned stocking was widely practiced. Of all introduced species, Oncorhynchus mykiss, Salmo trutta, and Salvelinus fontinalis thrived; they colonized almost any available water body in Andean Patagonia. In addition, Salmo salar and Salvelinus namaycush established self-sustaining populations at a few locations. The various populations that inhabit different water bodies seem to have diverged and given rise to what are believed to be particular stocks. Some of these became world-class sportfisheries and attained importance as generators of economic improvement. Simultaneously, and although no detailed studies exist, it has been thought that salmonids have a tremendous negative impact on the native biota. Thus, in less than 100 years, salmonids have been perceived as trophy sportfish, ecological nemeses, and promoters of social well-being through sportfisheries- associated economic development. In addition, the Chilean salmonid aquaculture boom led people to believe that this could be replicated in Argentine Patagonia and fostered the establishment of mostly O. mykiss caged-fish farming facilities. This raised concerns about a possible decrease in the quality of Argentine wild-salmonid (those salmonids that have successfully colonized and adapted to local waterways) sportfish- eries due to negative effects associated with escapement of aquacultured fish. This scenario may be realized because escaped individuals of Salmo salar, O. gorbuscha, O. keta, O. kisutch, O. nerka, and O. tshawytscha, all introduced in Chile, may be finding their way into Argentine rivers that drain into the Pacific Ocean. These complexities have generated three interest groups: (1) people concerned with possible ecological damage upon the native biota, (2) promoters of sportfisheries as generators

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

Abstract We 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; ...

Rb-Cs ratio as an indicator of fish diet in lakes of the Patagonia, Argentina.

The ratios of Rb to Cs contents were studied in five fish species from seven lakes located in the Patagonia Andean Range, Argentina in order to trace fish diet. The species studied were native velvet catfish (Diplomistes viedmensis) and creole perch (Percichthys trucha), and exotic brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvenilus fontinalis). Rainbow trout specimens from two farms were also studied, as well as fish food items and native mussels (Diplodon chilensis). Rb and Cs concentrations were determined by instrumental neutron activation analysis. A positive correlation of Cs concentration in the muscle of velvet catfish with fish length was observed, probably associated with the long biological half-life of this element in this species, whereas the Rb concentration remained constant, hence inhibiting the use of Rb-Cs ratios as a tracer in this case. Seasonal variations observed for rainbow trout and Cs concentration background bias in one of the lakes studied are also a limiting factor to the use of Rb-Cs ratios as a diet tracer. Rb-Cs ratios allowed clear differentiation of rainbow trout raised in farms from the natural specimens that lived in the same environment, in agreement with Rb-Cs ratios determined in both diets. Rb-Cs ratios in rainbow trout showed significant differences between Rivadavia and Futalaufquen lakes compared to Moreno and Nahuel Huapi lakes, which could be associated with a higher participation of plankton in the diet in the first case. No relevant variations in Rb-Cs ratios of brown trout were observed, probably because of the similarity in the diet.

Trace elements as fingerprint of lake of provenance and of species of some native and exotic fish of Northern Patagonian lakes.

A survey of trace element contents in fish muscle and liver was performed in different lakes of two northern Patagonian national parks: Nahuel Huapi and Los Alerces national parks. The aim of the work was to obtain the first set of reference data on elements that are not liable to be disturbed by human activities and to identify compositional patterns related to the species and site of collection. The species studied are native creole perch and velvet catfish and exotic brown trout, rainbow trout, and brook trout. The elements analyzed are Br, Cs, Fe, Rb, Se, Na, and Zn. Trace elements in muscle of brown trout, rainbow trout, and creole perch showed statistical patterns that allow one to identify the national park of origin, as well as which of the lakes (Traful, Espejo Chico, or the Nahuel Huapi-Moreno system) of the Nahuel Huapi National Park from which they come. Contents in the liver provide similar but less clear patterns than contents in muscle; however, in some particular cases, they provide additional information. Trace element contents in muscle are also good indicators of the species collected within a lake.