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Las presiones antrópicas que afectan los ecosistemas dulceacuícolas de Chile generan complejos efectos sobre la fauna de peces y lampreas. En este trabajo se analiza y resume la investigación científica que da cuenta de los impactos existentes y se propone una zonificación de amenazas basada en la distribución de las principales presiones antrópicas y los patrones distribucionales de las especies nativas de peces y lampreas de Chile. Esta evaluación permitió identificar las principales presiones a lo largo del país y los impactos empíricamente comprobados para esta fauna en los distintos niveles de organización, desde individuos a ecosistemas. El resultado de la evaluación revela que peces y lampreas de Chile están extremadamente amenazados por múltiples presiones antrópicas a lo largo del país y que se requiere de urgentes medidas efectivas de conservación para asegurar su persistencia. Por último, se propone un modelo de efectos en cascada desde la presión (actividad antrópica) que genera el impacto, a los cambios experimentados por la fauna de peces y lampreas a distintos niveles de su organización jerárquica y en distintas escalas espaciales y temporales. Esta propuesta de zonificación de amenazas y modelo de efectos en cascada pretenden ser una herramienta útil para facilitar la conservación de la valiosa fauna de peces y lampreas de Chile.

The global increase in human population is driving a continuous conversion of land to anthropogenic uses. This is a major threat to lotic ecosystems worldwide, as it compromises the biotic integrity and health of rivers and streams. Studies in the northern hemisphere have shown that the effects of urbanization on fish assemblages include decrease and/or loss of diversity and abundance of native species, and a proliferation of tolerant exotic species. Such effects have not been widely studied in developing countries like Chile, where urbanization has impacted several river ecosystems. Over decades, the lower zone of the Andalién River in Central Chile has gone over intense non-planned urbanization stemming from the city of Concepción, leading to several physical alterations. The native fish and lamprey fauna of this coastal river basin has been reported as very diverse, with a total of 16 native species. However, this fauna has been affected by multiple effects of different land uses and direct alterations in the riverbed. To study how these fish and lamprey assemblages have changed, this paper compiles records from 1919 to 2018 and analyzes them in relation to the direct and indirect anthropogenic alterations in the basin. The results show a significant reduction in richness and abundance of native species, with only nine species currently. The two migratory lampreys, one of them endemic (Mordacia lapicida), have been extirpated from the Andalién River basin. Conversely, the richness and distribution of introduced species has increased throughout the river basin. The invasive species Gambusia holbrooki, first registered in 1999, is currently the most abundant in the urban zone of the river. Although the more substantial direct alterations of the riverbed occurred in the lower areas, a steeper reduction in native species richness occurred in the middle areas subjected to a long history of agricultural and forestry land use. We suggest the loss of resilience of the river ecosystem, and that the collapse of biodiversity in this river system demonstrates the lack of urban planning and the inefficiency of environmental regulations in protecting native species and ecosystems with high conservation value in Chile.

Abstract An understanding of how genetic variability is distributed in space is fundamental for the conservation and maintenance of diversity in spatially fragmented and vulnerable populations. While fragmentation can occur from natural barriers, it can also be exacerbated by anthropogenic activities such as hydroelectric power plant development. Whatever the source, fragmentation can have significant ecological effects, including disruptions of migratory processes and gene flow among populations. In Chile, the Biobío River basin exhibits a high degree of habitat fragmentation due to the numerous hydroelectric power plants in operation, the number of which is expected to increase following new renewable energy use strategies. Here, we assessed the effects of different kinds of barriers on the genetic structure of the endemic freshwater fish Percilia irwini, knowledge that is critically needed to inform conservation strategies in light of current and anticipated further fragmentation initiatives in the system. We identified eight genetic units throughout the entire Biobío system with high effective sizes. A reduced effective size estimate was, however, observed in a single population located between two impassable barriers. Both natural waterfalls and human‐made dams were important drivers of population differentiation in this system; however, dams affect genetic diversity differentially depending on their mode of operation. Evidence of population extirpation was found in two river stretches limited by upstream and downstream dams. Significant gene flow in both directions was found among populations not separated by natural or anthropogenic barriers. Our results suggest a significant vulnerability of P. irwini populations to future dam development and demonstrate the importance of studying basin‐wide data sets with genetic metrics to understand the strength and direction of anthropogenic impacts on fish populations.

Longitudinal connectivity is the main attribute of river ecosystems and is essential for the maintenance of aquatic biota. When longitudinal connectivity decreases in a river network, abundance of some fish species decreases, and local extinctions may occur. Such abundance decreases and extinctions affect local assemblage structure (alpha diversity) and result in a high degree of dissimilarity among local assemblages (higher beta diversity). Specific ecological mechanisms that are behind these biodiversity changes induced by connectivity loss remain poorly understood. Here, we assessed the effects of fragmentation at the local and basin level, as well as local environmental variables on local fish diversity patterns in eight Andean river basins in central Chile (32–39° S). The results indicated that fish assemblages inhabiting pool habitats in highly fragmented basins were characterized by significantly lower species richness and alpha diversity mainly driven by absence of fish species with high dispersion capacities. Our results highlight the importance of the effects of barrier cascades upstream as drivers of local native fish diversity. Sustainable hydropower development necessitates system scale planning of the placement of future barriers and should consider both local and basin scale biodiversity indicators.

Abstract Background Fragmentation (establishment of barriers e.g., hydropower dams, reservoirs for irrigation) is considered one of the greatest threats to conservation of river systems worldwide. In this paper we determine the fragmentation status of central Chilean river networks using two indices, namely Fragmentation Index (FI) and Longest Fragment (LF). These are based on the number of barriers and their placement as well as river length available for fish movement. FI and LF were applied to eight Andean river basins of central Chile in order to assess their natural, current (2018) and future (2050) fragmentation at the doorstep of a hydropower boom. Subsequently, we exemplify the use of these indices to evaluate different placement scenarios of new hydropower dams in order to maximize hydropower use and at the same time minimize impact on fish communities. Results In the natural scenario 4 barriers (waterfalls) were present. To these 4 barriers, 80 new ones of anthropogenic origin were added in the current (2018) scenario, whereas 377 new barriers are expected in near future (2050). Therefore, compared to the ‘natural’ scenario, in 2050 we expect 115-fold increase in fragmentation in analysed river systems, which is clearly reflected by the increase of the FI values in time. At the same time, the LF diminished by 12% on average in the future scenario. The fastest increase of fragmentation will occur in small and medium rivers that correspond to 1st, 2nd and 3rd Strahler orders. Finally, case study on configuration of potential hydropower plants in the Biobío basin showed that hydropower output would be maximized and negative effects on fish communities minimised if new hydropower plants would be located in tributaries of the upper basin. Conclusions Fragmentation of Chilean Andean river systems is expected to severely increase in near future, affecting their connectivity and ecological function as well as resilience to other anthropogenic stressors. Indices proposed here allowed quantification of this fragmentation and evaluation of different planning scenarios. Our results suggest that in order to minimise their environmental impact, new barriers should be placed in tributaries in the upper basin and river reaches above existing barriers.

Body and head shape among fishes both vary between environments influenced by water velocity and across ontogeny. Although the shape changes associated with variation in average water velocity and ontogeny are well documented, few studies have tested for the interaction between these two variables (i.e., does ontogenetic shape variation differ between velocity environments). We use geometric morphometrics to characterize shape differences in Trichomycterus areolatus, a freshwater catfish found in high and low-velocity environments in Chile. We identify a significant interaction between velocity environment and body size (i.e., ontogeny). Ontogenetic patterns of shape change are consistent with other studies, but velocity environment differentially affects the ontogenetic trajectory of shape development in T. areolatus. Shape change over ontogeny appears more constrained in high-velocity environments compared to low-velocity environments.

Biotransport is often associated with migration patterns of species, including large, anadromous salmonids. Several studies have reported biotransport of persistent organic pollutants in the Northern Hemisphere, but there is no published information on biotransport ocurring south of the equator. Chile’s Patagonia is one of the last largely intact natural areas in the world. The objective of this study was to determine whether persistent organic pollutants are transported by the invasive Pacific Chinook salmon (O. tshawytscha) from the Pacific Ocean to Chilean Patagonia. Samples of juvenile and adult Chinook salmon were analyzed for polychlorinated biphenyls, pesticides and polybrominated diphenyl ethers. The results revealed that concentrations of POPs in adults migrating into Patagonian rivers were significantly higher than those found in juveniles migrating seaward. A mass balance analysis indicates that Chinook salmon are a source of persistent organic pollutants to Chilean Patagonia inland waters.Capsule: Biotransport of Persistent Organic Pollutants (POPs) by Chinook salmon (O. tshawytscha) from the Pacific Ocean to Chilean Patagonia has been confirmed by mass balance of POPs.

AimExotic species' introductions together with extinction of native species represent the main mechanisms driving biotic homogenization of freshwater fish assemblages around the world. While generally ichtyofaunistic realms transit towards biotic homogenization, for conservation purposes it is essential to understand what specific mechanisms are promoting it on particular areas or regions. Here, we report the occurrence of biotic homogenization in 29 Chilean watersheds, analyzing its β-diversity (including turnover and nestedness) and predicting future trends.LocationContinental Chile (18o-56o S).MethodsWe determined fish composition per basin for historical and current assemblages; extant native, exotic, and extinct species were recorded as 1 (presence) or 0 (absence) in two matrices basins × species. For each matrix, we calculated the turnover (βsim), nestedness (βnes), and β-diversity (βsor); then, we obtained Δβsim, Δβnes, and Δβsor, as the arithmetical difference between basin pairs over time. In addition, we search for explanatory variables correlating Δβsim, Δβnes, and Δβsor with geographical and land use variables. Finally, simulating events of species introduction (i.e., invasion) and extinction, we generated 15 hypothetical assemblages, looking to establish future trends towards biotic change in Chilean basins.ResultsSpecies turnover and β-diversity significantly decreased from historical to current assemblages (Δβsim = -0.084; Δβsor = -0.061, respectively), while the species nestedness did not show significant changes (Δβnes = 0.08). Biotic changes have been driven mainly by the introduction of 28 exotic species, with a minor role of extinctions (one species) and translocations (0 species) of native species. Changes in β-diversity were negatively correlated with area, elevation, and geographical distance between basins but not with land-use nor human population. Finally, the analysis of 15 future assemblages predicts a significant decrease of β-diversity and turnover, and an increase for species nestedness, this time promoted by an increase in the extinction of native species.Main conclusionChilean basins show a significant decrease of the distributional β-diversity and species turnover of the freshwater fish fauna, evidencing a trend towards biotic homogenization. This trend is shared with other Neotropical basins; however, specific mechanisms driving it show different magnitude. Changes in the β-diversity components do not show correlation with variables associated to land use, thus suggesting that casual introductions of freshwater fishes in Chile follow an opportunistic mode related to commercial use. According to future scenarios simulated, biotic homogenization should increase further, mainly as consequence of increased native extinctions.

Studies at local and global scales have showed that fish freshwater communities are going through a process of biotic homogenization, due mainly to exotic species introduced from other regions, and to the extinctions or extirpations of native species. Here we analyze the compositional changes among the contiguous biogeographic regions of continental Chile, expecting an important homogenization for being contiguous. By means of the spatial turnover (βsim index), we determined the patterns of the compositional change and biotic homogenization from “historical” (βsim,H; calculated before the introduction of exotic species by post-European colonization) to “current” (βsim,C; calculated after the introduction of exotic species carried out by European colonizers) time. The differential turnover (Δβsim) exhibited an average of −0.04 and showing a significant distribution, with a median different from zero (P

Abstract Aim River systems of Central Chile are short, steep and fast flowing. They are characterized by discharge regimes dominated by rainfall and snowmelt. Invertebrate fauna is highly endemic. This study aimed to describe the community structure of invertebrate in eight river systems in Central Chile (33-39°S) using species co-occurrence and niche sharing null models. Methods Invertebrate samples were collected from Central Chilean rivers (33-39°S), data were analyzed co-occurrence species and niche sharing null models for determine potential structuring patterns. Results The results revealed the presence of non-structured patterns in co-occurrence considering each site as well as all sites, that is most probably an effect of presence of many repeated species in the studied sites. Furthermore, we found the existence of niche overlap due to interspecific competition at each site and among all sites. The results obtained from these river systems corroborate observations from Chilean Patagonian Rivers. Conclusion This study contributes to understanding of biogeographical and ecological patterns of invertebrate communities in central Chilean Rivers and provide foundations for more complex ecological studies.

Galaxiid fishes from South America are represented by three genera (Aplochiton, Brachygalaxias and Galaxias) and eight species. Their genetic patterns have been studied over the last two decades to disentangle how historical and contemporary processes influenced their biogeographic distribution and phylogeographic patterns. Here we review and synthesize this body of work. Phylogeographic approaches reveal the important role played by orogeny and the expansion/melting of glacial ice during the Quaternary. Populations retreated to glacial refugia during glacial times and some systems experienced drainage reversals from the Atlantic to the Pacific following deglaciation. Although most species expanded their populations and increased their genetic diversity during the Holocene, the introduction of salmonids and the construction of dams are likely to lead to a decline in genetic diversity for at least some species. An improvement in our understanding of the processes that influenced historical and contemporary diversity patterns among galaxiid and other native fishes in South America is necessary for addressing the cumulative and synergistic impacts of human activity on this unique freshwater fauna.

South American galaxiids occupy both Patagonia and the ichthyogeographic Chilean Province, encompassing glacial Andean deep lakes, shallow plateau lakes, reservoirs, short Pacific rivers and long Atlantic rivers. The total fish fauna includes 29 species, comprising Neotropical fishes (siluriforms and characids), galaxiids, percichthyids, atherinopsids and mugilids, two lamprey species, and several exotic fishes (salmonids, Gambusia spp. and common carp). The family Galaxiidae shares a common ancestry with the Gondwanan temperate fish fauna, played a major role in the post-glacial colonization of Andean lakes and streams, and contributes key species to the food webs. Galaxiid species occupy an enormous latitudinal gradient, show a wide variety of life history patterns and are the southernmost native freshwater fishes of the world. Knowledge of South American galaxiids has improved notably, but new challenges arise due to climate change, biological invasions, damming, aquaculture and contamination. In this changing environment, the future of South American galaxiids should be carefully considered as a legacy of the old Gondwana and a unique attribute of the freshwaters of southern South America.

Body and head shape in fish responds to environmental factors such as water flow rate, food sources, and niche availability. However, the way in which fish respond to these environmental factors varies. In Central Chile, multiple river and lake systems along the coast provide an ideal study site to investigate these types of shape changes. We use geometric morphometrics to characterize shape differences in Galaxias maculatus (Jenyns) between river and lake populations. Lake fish converge on a shape with a more fusiform body, narrower head, and larger eyes, while river fish have a more robust body, rounder head, and smaller eyes. These shape changes are consistent with a shift to zooplanktivorous foraging in lakes, as evidenced in other systems. Unlike some fish species that develop polymorphisms in body shape after colonization (e.g., benthic and limnetic forms), G. maculatus in lakes exhibit a monomorphic limnetic form.

ABSTRACT We document movement patterns and home range of Diplomystes camposensis, an endemic and threatened freshwater catfish from Chile. We tracked the movements of seven individuals of different body size (13.5 to 19 cm SL) using portable radio telemetry equipment to investigate movement patterns in relation to day/night activity and habitat use in the San Pedro River (Valdivia Basin). Tracked movements and model-based analyses revealed that D. camposensis has a large home range and high mobility. The average home range was 0.068163 ± 0.033313 km2, and the average area of higher activity was 0.005646 ± 0.011386 km2. The mean linear home range was 387.4 m. The results also showed that movements were longer during the night, supporting nocturnal habits. Movements tended to be in an upstream direction for some individuals, although these differences were not significant when data was pooled. Large home range and movements suggest that the species may require large river areas to meet ecological demands, an aspect that could be severely affected by fragmentation. These results, along with previously published genetic data, suggest that the conservation of D. camposensis would be seriously threatened by hydromorphological alterations (e.g. lack of connectivity), such as those resulting from dam building.

La relación longitud-peso y el factor de condición (K) son descriptores de gran interés en la biología de poblaciones de peces, ya que aportan información fundamental sobre estrategias de crecimiento, estado nutricional y reproducción. También son parámetros ampliamente utilizados para comparar la condición de poblaciones que habitan en sistemas acuáticos con distintos grados de intervención antrópica. Por ello, conocer el comportamiento de poblaciones que habitan en ecosistemas prístinos, entrega información de base, relevante para comprender cambios o efectos en poblaciones sometidas a estas presiones. El río San Pedro de la cuenca del Valdivia, sur de Chile, es un sistema que se caracteriza por su actual bajo nivel de intervención, su alta diversidad íctica y baja abundancia de especies introducidas. En este trabajo describimos la relación longitud-peso y factor de condición de 12 especies de peces nativos del río San Pedro, durante más dos ciclos anuales, analizando sus estrategias de crecimiento y variabilidad estacional del factor de condición. Los resultados de la relación longitud-peso muestran que gran parte de las especies presentan un crecimiento isométrico, especialmente Diplomystes camposensis, Basilichthys australis y Brachygalaxias bullocki. Sin embargo, algunas especies presentan una tendencia a la alometría (Galaxias maculatus, Galaxias platei y Trichomycterus areolatus). Los valores de K muestran que especies como Percilia gillissi poseen una marcada variabilidad anual, posiblemente asociada a las épocas reproductivas y de mayor oferta de alimento. Entregamos esta información como base para entender el funcionamiento de poblaciones ícticas en condiciones naturales y para ser utilizada en la evaluación de futuros proyectos que puedan impactar estos ecosistemas.The length-weight relationship and condition factor (K) are useful descriptors in population fish biology, because they provide essential information on growth strategies, nutritional status and reproduction. They are also parameters widely used to compare the condition of aquatic systems with varying degrees of human intervention. Therefore, understanding the dynamics of populations in pristine ecosystems, provides relevant basic information to understanding changes or effects in populations under these pressures. The San Pedro river (Valdivia basin), southern Chile, is a system characterized by its current low intervention level, high fish diversity and low abundance of introduced species. We describe the length-weight relationship and condition factor of 12 native fish of the San Pedro river, for over two annual cycles, analyzing their growth strategies and seasonal variability in condition factor. The results of the length-weight show that the most of species exhibit isometric growth, especially Diplomystes camposensis, Basilichthys australis and Brachygalaxias bullocki, however, some species have a tendency to allometry (Galaxias maculatus, Galaxias platei and Trichomycterus areolatus). The values of K show that species such as Percilia gillissi have a strong annual variability, associated with the breeding season and greater supply of food. We give this information as baseline data to understand the functioning of fish populations in natural conditions and to be used for the evaluation of future projects that may impact these ecosystems.

En sistemas fluviales, las comunidades biológicas están estructuradas principalmente por el hábitat físico. Conocer el tipo de hábitat que ocupa cada especie a lo largo de su vida es fundamental para comprender su ecología en sistemas naturales y definir estrategias de conservación en sistemas alterados. Por ello, aquí caracterizamos el uso de hábitat de 12 especies de peces nativos del río San Pedro. Se capturaron 37334 individuos de las 13 especies nativas presentes en el río. Los hábitats más muestreados y con mayores capturas totales fueron pozas someras y rápidos someros. Las especies más abundantes fueron Percilia gillissi, Galaxias maculatus, Galaxias platei y Trichomycterus areolatus. Se observa un uso diferenciado del hábitat por especie, en que los Galáxidos son más abundantes en zonas de baja velocidad (pozas) y los Siluriformes en zonas de alta velocidad (rápidos). Además, reconocemos el uso diferenciado del hábitat con la talla en Aterinópsidos y Percichthys trucha, en que los adultos ocupan principalmente los ambientes lacustres y sus juveniles las zonas fluviales ribereñas.In fluvial systems, the biological communities are mainly structured by the physical habitat. Knowing the habitat that each species use throughout its life is fundamental to understand its ecology in natural systems and to define conservation strategies in altered systems. For that reason, here we characterize the habitat use of 12 native fish species of the San Pedro River. 37344 individuals of the 13 native species occurring in the river were caught. Shallow ponds and shallow rapids were the most sampled habitats and had the largest captures. The most abundant species were Percilia gillissi, Galaxias maculatus, Galaxias. platei and Trichomycterus areolatus. A differentiated habitat use per species is notices, where the Galaxiids are more abundant in areas of slow velocity (ponds) and the Silurids in areas of high velocity (riffles). Moreover, we recognized a differentiated habitat use based on the size of Atherinopsidae and Percichthys trucha, where adults mainly occur in the lake and their juveniles occur in the borders of fluvial zones.

El río San Pedro corresponde al sistema fluvial que desagua la cadena de ocho lagos andinos de la cuenca del río Valdivia (Región de los Ríos). Este sistema recorre 40 km entre el desagüe del lago Riñihue y su confluencia con el río Collileufu, donde cambia de nombre a río Calle Calle. En él se proyectó construir la "Central Hidroeléctrica San Pedro", cuyo muro se ubica 14 km aguas abajo del desagüe del lago Riñihue y la cual transforma 12,5 km de río en embalse. Ello generó la necesidad de elaborar un Estudio de Impacto Ambiental, el cual fue desarrollado por el Centro de Ciencias Ambientales Eula Chile (Universidad de Concepción). En relación a la ecología del río, dicho estudio puso especial énfasis en generar el conocimiento de detalle sobre su ictiofauna, con el fin de efectuar una evaluación de impactos especie específica. En este artículo presentamos los fundamentos y aproximaciones metodológicas para llevar a cabo el estudio intensivo, cuyos resultados dan origen a esta publicación monográfica y a la descripción de la distribución, abundancia, uso de hábitat, patrones de desplazamiento, relaciones de longitud-peso, primeros estadíos de vida y estructura genética de la ictiofauna del río San Pedro.The San Pedro River is the fluvial system being drained by the chain of eight Andean lakes in the Valdivia River Basin (de los Ríos Region). This system covers 40 km from the outlet of Riñihue Lake to its confluence with the Collileufu River, where it is renamed as Calle Calle River. In the San Pedro River, the "Central Hidroeléctrica San Pedro" (San Pedro Hydroelectric Plant) is planned, whose dam is located 14 km downstream from the outlet of the Riñihue Lake, which will transform 12.5 km of river in a reservoir. This generated the need for an Environmental Impact Assessment, which was developed by the Center for Environmental Sciences EULA-Chile (Universidad de Concepción). In relation to the river ecology, the study placed special emphasis on generating detailed knowledge about their ichthyofauna, in order to make a species-specific impact assessment. In this issue, we present the foundations and methodological approaches to undertake the intensive study, whose results give rise to this monograph and to the description of the distribution, abundance, habitat use, movement patterns, length-weight relationships, early life stages and genetic structure of the fish fauna of San Pedro River.

Basado en muestreos de tres años consecutivos y revisión de literatura, describimos la composición, singularidad y estado de conservación de la ictiofauna del río San Pedro, en la cuenca del río Valdivia. Además, analizamos los posibles orígenes de esta ictiofauna, postulando que parte de la cuenca del río Valdivia ha funcionado como un sumidero, principalmente su parte alta, con aportes de fuentes tanto costero-Pacíficas como del Este de Los Andes. Concluimos que el río San Pedro es de particular valor ictiofaunístico por su alta riqueza específica, endemismos y características biogeográficas.Based on three consecutive years of sampling and bibliographic revision, the composition, singularity and conservation status of the San Pedro River ichthyofauna is described. In addition, the potential origin of this Valdivia River ichthyofauna was analyzed and this basin is proposed to have worked like a sink, mainly the higher zone, having been colonized both from Coastal-Pacific as from Eastern Andes sources. It is concluded that this river has a particular conservation value due to its high species richness, endemism and biogeographic characteristics.

Los peces nativos chilenos se caracterizan por ser de tamaño pequeño (The Chilean native fish are characterized for having small sizes (< 30 cm). Due to this, they are generally described with a low swimming capacity and movement; nevertheless, there is no empirical study to show it. In this study we describe the movement patterns of six native species in the San Pedro River (Aplochiton taeniatus, Galaxias maculatus, Galaxias platei, Diplomystes camposensis, Basilichthys australis y Percilia gillissi) by using marking-recapture techniques with elastomeric inks and Pit tags. Our results suggest that most of the species show passive movements, crossing distances up to about 40 km in the flow direction. Movements between river banks were also frequent, even in zones of high turbulence of the river. Active movements upstream were note clear, but the analysis of the results altogether with information of the genetic structure, abundances and distribution of the species in the watershed, allows us to conclude that the movement patterns of all species studied are relevant for the maintenance of their metapopulation dynamics.

Los estadios de huevos, larvas y juveniles de los peces de agua dulce nativos de Chile son prácticamente desconocidos. Conocer su estacionalidad, morfología y uso de hábitat es relevante para comprender su biología y permitir la conservación de esta ictiofauna altamente amenazada. Asimismo, los primeros estadíos del ciclo de vida de los peces determinan la persistencia de las poblaciones en el tiempo. Dado esto, el objetivo del presente trabajo fue dar a conocer y describir los resultados de intensivos muestreos (465 días) destinados a encontrar los primeros estadíos de las 14 especies nativas que habitan el río San Pedro (cuenca del Valdivia). Los muestreos se efectuaron desde octubre de 2005 a marzo de 2008. Se encontraron huevos, larvas y juveniles de Galaxias maculatus, Basilichthys australis y Percilia gillissi; larvas y juveniles de Geotria australis y Trichomycterus areolatus, y juveniles de Diplomystes camposensis, Percichthys trucha y Cheirodon australe. En cada caso se describe la época y hábitat de ocurrencia, así como sus características morfológicas generales, lo cual para P. gillissi constituye la primera descripción de sus estadíos de desarrollo embrional y larvario. En general, se aprecia una segregación espaciotemporal de las épocas de desove y crianza de larvas marcada por el uso de las planicies de inundación como sitios de crianza. La extensión temporal de este estudio a escala de ambientes ribereños sugeriría que los esfuerzos de búsqueda de aquellos primeros estadíos no detectados podrían enfocarse en ambientes más profundos o correntosos.Eggs, larvae and juveniles stages of the Chilean native freshwater fish are practically unknown. To know their seasonality, morphology and habitat use is relevant to understand their biology and to allow the conservation of this highly threatened ichthyofauna. Likewise, the early stages of fish's life cycle are highly labile and their success determines the persistence of the populations over time. For this reason the aims of this work is to report and describe the results of intensive samplings performed to find the early stages of the 14 native species that inhabit in the San Pedro River (Valdivia river Basin). Samplings were done during 465 days along the river, from October 2005 to March 2008. We found eggs, larvae and juveniles of Galaxias maculatus, Basilichthys australis and Percilia gillissi, larvae and juveniles of Geotria australis and Trichomycterus areolatus; and juveniles only of Diplomystes camposensis, Percichthys trucha and Cheirodon australe. We describe the season and habitat of occurrence, as well as their general morphological characteristics. This is the first description of embryonic and larval development stages for P. gillissi. A spatial-temporal segregation of the spawning and larvae rearing is observed, mainly marked by the use of the floodplain as rearing sites. The temporal extention of this study at riparian scale suggests than efforts in search of early stages of knowless species would be focus in deeper and/or rushing environments.

El conocimiento de la dinámica natural de las comunidades biológicas en sistemas fluviales es relevante para la conservación de estos complejos ecosistemas. El río San Pedro, ubicado en la zona sur de Chile (39°46' - 39°51' S), es un sistema que posee una alta naturalidad dado el bajo nivel de perturbaciones antrópicas significativas. En una condición natural como ésta, el régimen de caudal determina en gran medida la dinámica de sus hábitats en el sentido longitudinal, lateral y temporal del río, influyendo a su vez en la distribución de las especies. De esta forma, la diferenciación hidrogeomorfológica a lo largo del río así como la variación a través del año, genera ensambles altamente dinámicos, tanto a nivel espacial como temporal. Con el fin de conocer la dinámica natural de las comunidades ribereñas de peces, estudiamos la estructura comunitaria a lo largo de tres zonas hidrogeomorfológicas del río San Pedro, denominadas macrozonas. También analizamos la dinámica temporal de los ensambles de peces para conocer cambios estructurales entre las épocas de alto y bajo caudal, asociados a la dinámica de las planicies de inundación. Para la determinación de los patrones espacio-temporales, se realizaron muestreos periódicos en el río San Pedro durante dos ciclos anuales (2006-2007) y se estimaron índices de diversidad clásicos y análisis de agrupamiento basados en similitud. Complementariamente, se realizaron muestreos en diferentes sectores de la cuenca para comparar las tres macrozonas presentes en el río y determinar el grado de singularidad del sistema. Los resultados sugieren la presencia de ensambles ícticos diferenciados a lo largo del río, principalmente entre la macrozona 1 (primer tramo) y 2 (segundo tramo), debido a la predominancia de ambientes más lénticos en la primera y de grandes rápidos en la segunda. Temporalmente, el aumento en las precipitaciones origina ambientes inundados en áreas terrestres. Esto influye en una reducción de la abundancia y diversidad de especies de peces en la época de alto caudal. En contraste, en la época de bajo caudal dominan los ambientes someros, y aumentan tanto el número de individuos como la riqueza específica. La ictiofauna del río San Pedro difiere en su composición y estructura de aquella que habita en otros sectores de la cuenca, lo cual lo convierte en un ecosistema altamente singular.The knowledge of the natural dynamic of the biological communities in fluvial systems is relevant for the conservation of these complex ecosystems. The San Pedro River, located in the South of Chile, is a system that has a high naturalness due to the absence of significant anthropogenic intervention. In systems under a natural dynamic like this one, the flow regime determines mostly the habitat dynamics, affecting also the species distribution. This generates highly dynamic assemblages at the spatial and temporal levels. Hence, we studied the fish community structure along three hydrogeomorphological zones of the San Pedro River, named macrozones, to understand the natural dynamic of the freshwater fish communities. In addition, we analyzed the temporal dynamics of the fish assemblages in order to know structural changes between high and low flow seasons, associated to the dynamic of floodplains. Periodic fish samples were done in the San Pedro River during two annual cycles (23 months) to determine the spatial-temporal patterns, and to asses classic diversity indexes and clustering analysis based on similarity. Complementarily, fish samples were collected in different places of the basin to compare the three macrozones occurring in the river and to determine the degree of singularity of the system. The results suggest the occurrence of different fish assemblages along the river, mainly between the macrozone 1 and 2, due to the predominance of lentic habitats in the first one and large rapids in the second one. Temporarily, the augment in rainfall cause flooded habitats in dry land areas, increasing the extent and heterogeneity of the river habitats. This produces a reduction in the fish species' abundance and diversity during the high flow season. In contrast, shallow environments are dominant during the low flow season, and there is an increment both in the number of individuals and in the specific richness. The San Pedro River's ichtiofauna differs in composition and structure to those in other sectors of the basin, which makes it a highly singular ecosystem.

Estudiamos los niveles y patrones de variabilidad genética de ocho especies de peces nativos de la cuenca del río San Pedro (cuenca del río Valdivia, Región de los Ríos, Chile), con el objetivo de evaluar diferencias microevolutivas en especies sometidas a similares condiciones ecológicas e históricas. Las especies consideradas fueron: Diplomystes camposensis, Percilia gillissi, Galaxias platei, G. maculatus, Basilichthys australis, Percichthys trucha, Aplochiton taeniatus y A. zebra. Para ello comparamos indicadores de diversidad genética tanto intra como inter-zonas, e indicadores de estructuración, basados en secuencias de la región de control, para diferentes tramos a lo largo del desarrollo del río. También recuperamos relaciones de parentesco entre haplotipos y su distribución espacial, para cada especie, a partir de redes construidas por parsimonia estadística. Además estimamos indicadores de comportamiento demográfico en el pasado (D de Tajima, Fs de Fu y distribución de frecuencias de diferencias pareadas). Los resultados sugieren que, tanto los patrones de diversidad genética en el río, como las respuestas demográficas, son especie específicos. Las especies más variables, conjuntamente con un alto grado de estructuración y bajo flujo génico en el río son G. maculatus y A. taeniatus. P. trucha mostró altos niveles de estructuración pero valores menores de variabilidad que el par de especies anterior. Las especies menos variables y menos subdivididas en la cuenca son Diplomystes camposensis y P. gillissi. Las demás especies mostraron niveles de variabilidad y estructuración intermedios entre los patrones extremos señalados para las especies anteriores. Las diferencias entre especies se atribuyen a atributos biológicos idiosincráticos tales como nivel de especialización en el uso de hábitat acuático, abundancias poblacionales históricas y comportamientos migratorios. En el caso de Galaxias maculatus, los altos niveles de variabilidad son atribuidos a la mantención histórica de altos tamaños poblacionales, gracias a la posibilidad de usar tanto hábitats marinos como dulceacuícolas. Mientras que los bajos niveles de diversidad e indicadores de variación histórica de tamaños efectivos poblacionales, sugieren que Diplomystes camposensis y Percilia gillissi fueron especies más sensibles y sometidas a reducciones poblacionales en el pasado. Se discuten los resultados en torno a factores ecológicos, biológicos e históricos.We studied the levels and patterns of genetic variability in eight species of native fishes from the Valdivia River Basin (Región de los Rios, Chile), with the aim to estimate microevolutionary differences in species with similar ecological and historical conditions. The species considered were Diplomystes camposensis, Percilia gillissi, Galaxias platei, G. maculatus, Basilichthys australis, Percichthys trucha, Aplochiton zebra and A. taeniatus. We compared genetic diversity indexes both intra and inter-zones, and genetic structure, based on sequences of the control region for different sections along the river. In addition, we recovered relationships among haplotypes and their spatial distribution for each species, based on statistical parsimony networks. Estimators of past demographic behavior (D Tajima, Fs-Fu and mismatch analysis were also obtained. The results suggest that both patterns of genetic diversity in the river such as demographic responses are species specific. The most variable and strongest structured species in the river were G. maculatus and A. taniatus. P. trucha showed high structure values but its genetic variation was lower than the first two species. The less variable and less subdivided species were D. camposensis and P. gillissi. The remaining species showed levels of variability and structure intermediate between the two extreme patterns mentioned above. The differences among species are attributed to idiosyncratic biological attributes such as level of specificity in the use of aquatic habitat, population abundances, and historical migration patterns. In the case of G. maculatus, high levels of variability are attributed to the historical maintenance of high and stable effective population sizes, due to the ability to use both marine and freshwater habitats. Low levels of genetic diversity and indicators of historical reduction in effective population size, suggests that D. camposensis and P.gillissi were more sensitive and more exposed to population reduction. Results are discussed regarding ecological, biological, and historical factors.

Los ecotonos transicionales entre lagos y ríos han recibido menor atención que aquellos de ecosistemas terrestres, y pueden reunir características particulares de gran importancia para la conservación de la biodiversidad dulceacuícola. Con el objeto de evaluar lo anterior, se estudió la dinámica espacio-temporal de las abundancias y tallas, de poblaciones de 13 especies de peces nativos chilenos, presentes en la zona ecotonal Lago Riñihue - Río San Pedro, ubicada en la cuenca hidrográfica del río Valdivia (Chile). Se muestrearon mensualmente 35 sitios localizados en tres zonas hidromorfológicas del área de estudio (número de sitios por zona: Ml = 9, M2= 17, M3= 9). Los muestreos se llevaron a cabo el año 2006. De manera complementaria, se realizaron muestreos en todos los sitios los años 2007 (enero - febrero, junio - agosto y diciembre) y 2008 (enero - marzo). Los resultados de este estudio muestran la presencia de un ecotono muy dinámico tanto espacial como temporalmente, apoyando la hipótesis que estas zonas transicionales poseen características especiales que deben ser tomadas en consideración para la conservación de la biodiversidad.The transitional ecotones between lakes and rivers have received less attention than those of terrestrial ecosystems and can meet particular characteristics of great importance for freshwater biodiversity conservation. In order to evaluate this, we studied the spatio-temporal dynamics of the abundances and body sizes of the populations of 13 species of Chilean native fishes, in the ecotonal area Riñihue Lake - San Pedro river, located in the Valdivia river basin (Chile). Thirty five sites were sampled monthly, located in three hydromorphological zones of the study area (number of sites by area: M1 = 9, M2 = 17 M3 = 9). The results of this study show the presence of a dynamic ecotone both spatially and temporally, supporting the hypothesis that these transitional zones have special characteristics that must be taken into account for conservation of biodiversity.

La presencia de salmón Chinook asilvestrado se ha reportado en Chile desde 1995 con un aumento de la frecuencia de las corridas hacia ríos patagónicos y el consecuente asentamiento temporal de poblaciones juveniles. Con el fin de comprender las implicancias ecológicas de la presencia de estas nuevas poblaciones de juveniles de Chinook en ríos y lagos patagónicos, estudiamos la dieta, condición y edad de individuos de 4 cuencas del sur de Chile (río Puelo, Blanco, Aysén y Futaleufú). Para ello analizamos 104 individuos, 67 provenientes de lagos y 37 provenientes de sistemas fluviales. Algunos juveniles capturados en las cuencas de Aysén (río Aysén) y Futaleufú (lago Yelcho) presentaron edades mayores a 1 año, los cuales corresponden a poblaciones "stream type". Por el contrario, en las cuencas del Blanco, Puelo y Futaleufú (sistemas fluviales) se encontraron juveniles únicamente de edad 0+. Individuos de ambas edades sólo coexistieron en el lago Yelcho. Los individuos de edad 1+ presentaron altos factores de condición y dietas piscívoras, basada en galáxidos nativos. Los individuos menores a 1 año presentaron factores de condición inferiores y una dieta basada principalmente en insectos de origen alóctono. Entre los individuos de edad 0+, sólo aquéllos mayores a 8,5 cm de largo total presentaron peces en sus estómagos. Concluimos que los juveniles de Chinook ingresan a los sistemas patagónicos como depredadores a partir del año de edad, aun cuando si alcanzan tallas mayores a 8,5 cm antes del año también se comportan como ictiófagos. En todos los casos, los peces presa correspondieron a peces nativos. Ello implica una nueva interacción negativa para la fauna íctica nativa patagónica, mediada por el tamaño de los peces introducidos, la cual se manifiesta tanto en depredación como eventualmente por competencia por organismos alóctonos, los cuales son una fuente importante de energía en sistemas oligotróficos como los patagónicos.The presence of feral Chinook salmon has been reported in Chile since 1995, since when it has been reported an increase in the frequency of runs into rivers of Patagonia and the consequent temporary settlement of juvenile populations. In order to understand the ecological significance of the presence of these new populations of juvenile Chinook in rivers and lakes, we analyze the diet, condition and age of individuals present in four basins of southern Chile (Puelo, Blanco, Aysen and River basins). We analyzed 104 individuals, 67 from 37 from lakes and river systems. Some juveniles caught in the Aysén watershed (river Aysén) and (lake Yelcho) had ages greater than 1 year, which correspond to "stream type" populations. By contrast, in the basins of Blanco, Puelo and Futaleufú (river systems) only age 0 + individuals were found. Juveniles of both ages coexisted only in lake Yelcho. The individuals of age 1 + showed high condition factors and piscivorous diets, based in native Galaxids. Individuals of less than 1 year showed lower condition factors and diets based mainly on insects of allochthonous origin. Among individuals of age 0 +, only those greater than 8.5 cm in total length had fish in their stomachs. We conclude that age 1 juvenile Chinook enter Patagonian systems as piscivore predators, and if they reach sizes greater than 8.5 cm before the completion of the first year they also behave as piscivores. In all cases, prey fish were composed of native fish. This suggests a new negative interaction for the native fish fauna of Patagonia, mediated by the size of exotic fish, such as predation, and possibly also competition for allochthonous organisms, which are an important source of energy in oligotrophic systems as the Patagonian.

Behavioral and physiological mechanisms of thermoregulation in ectotherms are conditioned by thermal constraints. These mechanisms may be even more restrictive when environmental conditions are unfavorable for individuals, especially when sexual dimorphism segregates the sexes spatially. In order to understand behavioral and physiological regulation mechanisms, we investigated the thermal biology of Phymaturus palluma (Molina, 1782), a sexually size dimorphic, high-mountain lizard that inhabits extreme climatic conditions. P. palluma showed a bimodal activity pattern, a major peak in the morning (11:00-13:30h) and in the afternoon (15:30-18:00 h). The lizards were more active when substrate temperatures were between 25 and 28º C. The highest abundance was found around 27º C (between 11:00-12:30). Females showed greater activity than males in the early morning. Sub-adults and juveniles did not show differences in their activity pattern. There was a positive relationship between body temperature and air and substrate temperatures, suggesting typically thigmothermal regulation.

Las comunidades de peces de agua dulce presentan grados de resistencia y resiliencia a actividades antrópicas, los cuales se relacionan positivamente con su diversidad específica y negativamente con los niveles de intervención previa. Los ríos costeros de la zona Centro-Sur de Chile se caracterizan por albergar una diversa ictiofauna, principalmente en sus zonas bajas. En particular, el sector de potamón de los ríos Andalién y Nonguen, ambos insertos en la ciudad de Concepción, son de alto valor de conservación de su biodiversidad. En estos sectores, los eventos recurrentes de inundación de zonas residenciales, construidas en las planicies de inundación, han llevado a que ambos cauces sean dragados y semicanalizados. Las respuestas de las comunidades de peces a este tipo de intervención no han sido estudiadas en Chile. Postulamos que dada su alta diversidad, y bajo nivel de intervención previa, las comunidades ícticas de los ríos Andalién y Nonguen son resistentes y resilientes a los efectos del dragado. Para entender la respuesta comunitaria en ambos ríos, en este estudio primero analizamos los cambios en la estructura en las situaciones previo al dragado, con acciones de dragado y posterior a las mismas. En segundo lugar, analizamos las respuestas especie-específicas, para explicar los cambios comunitarios y conocer la sensibilidad de las distintas especies a esta intervención. Inmediatamente después del dragado se produjo una disminución de la diversidad específica, generándose la dominancia de una única especie, Cheirodon galusdae. Posteriormente, se evidenció una recuperación parcial de los parámetros comunitarios. Basados en las respuestas especie-específicas a este tipo de perturbación identificamos 3 especies resistentes, 3 especies resilientes y 8 especies sensibles. De estas últimas, Nematogenys inermis es la de mayor relevancia en términos de conservación.The freshwater fish communities present degrees of resistance and resilience to human activities, which have a positive relationship with species diversity, and a negative relation with levels of previous intervention. The costal rivers in the Central-Southern zone of Chile are characterized by a diverse icthyofauna, principally in the low zones. Particularly, the potamon areas of the Andalién and Ñonguen rivers, both running through the city of Concepción, have a high conservation value of biodiversity. In these areas, the reoccurring flooding in residential zones constructed over the fioodplain has caused both channels to be dredged and semi-canalized. The fish community's response to this type of interventions has not been studied yet in Chile. We propose, given its high diversity and low level of previous intervention, that the fish community of the Andalién and Nonguen rivers is resilient to the effects of the dredge. To understand the community response in both rivers, we first analyzed the changes in the structure in situations before the dredge, with dredge actions, as well as after the dredge. Second, we analyzed the species-specific response to explain the community changes and be able to understand the sensibility of the different species to this intervention. Immediately after the dredge, a decrease of the species diversity occurred, generating the dominance of a single species, Cheirodon galusdae. Later, a partial recovery of the community parameters was noted. Based on species-specific responses of this type of perturbation, we identified 3 resistant species, 3 resilient species and 8 sensitive species. Among these last species, Nematogenys inermis has the highest relevance in conservation terms.

Field observations revealed, for the first time, cases of predation on Gordius austrinus by Salmo trutta in Risopatrón Lake, Aysén Region, Chile. Reinvestigation by SEM of the characteristics of the posterior end and of the cuticle of the specimens of horsehair worms collected inside the stomach of brown trout allow us to assign the specimens to the species Gordius austrinus. Also we could show that in some specimens the cuticle of mid body and terminal end presented structural alterations, due to the action of the digestive juices of the fish. This finding implies the extension of the distribution range of G. austrinus.En trabajos de campo se pudo observar, por primera vez, casos de depredación de Salmo trutta sobre Gordius austrinus en el Lago Risopatrón, Región de Aysén, Chile. El análisis ultraestructural (MEB) realizado sobre los especímenes de gordiidos, colectados dentro del estómago de la trucha café, sobre las características del extremo posterior y la cutícula, permitieron asignarlos a la especie Gordius austrinus. Asimismo, mostró que en algunos especímenes la cutícula de la región media del cuerpo y el extremo posterior presentaban alteraciones en su estructura, probablemente debidas a la acción de los jugos digestivos del pez. Este hallazgo implica la ampliación del rango de distribución de G. austrinus.

La ictiofauna nativa de los sistemas límnicos de Chile se compone de 11 familias, 17 géneros y alrededor de 44 especies, incluyendo dos lampreas. De éstas, 81% son endémicas de la provincia biogeográfica chilena y 40% se encuentran clasificadas en peligro de extinción. Los grupos más representados corresponden a los órdenes Siluriformes (11 especies), Osmeriformes (9 especies) y Atheriniformes (7 especies). También están representados en Chile los ciclóstomos Petromyzontiformes (2 especies), y los teleósteos Characiformes (4 especies), Cyprinodontiformes (6 especies), Perciformes (4 especies) y Mugilifromes (1). Latitudinalmente, la mayor riqueza de especies ocurre en la zona centro-sur de la provincia Chilena, en tanto que los extremos norte y sur son de baja riqueza específica. Dado su origen, porcentaje de endemismo y retención de caracteres primitivos, este conjunto ictiofaunístico es de alto valor biogeográfico y de conservación. Existen sin embargo importantes vacíos de conocimiento sobre su sistemática, distribución y biología.The Chilean native freshwater ichthyofauna is composed of 11 families, 17 genera and about 44 species, including two lampreys. The Chilean biogeographic province has 81% of the species endemic, 40% of which are classified as endangered. The most abundant groups are the siluriforms (11 species), osmeriforms (9 species) and atheriniforms (7 species). Other groups represented in Chile are the cyclostomous Petromyzontiformes (2 species), and the teleostean characiforms (4 species), cyprinodontiforms (6 species), perciforms (4 species) and mugiliforms (1). The South Central area of the Chilean Province has the highest species richness, whereas the northern and southern areas are poorer in species numbers. Due to its origin, percentage of endemism and primitive characters, the ichthyological fauna of Chile has a high biogeographic and conservation value, however, there are important knowledge gaps in the systematics, distribution and biology of these freshwater fishes.

Doce de las dieciséis especies de peces presentes en la cuenca del río Itata ingresan al menos en una época del año a los canales de riego, constituyendo un hábitat frecuentemente utilizado por la ictiofauna nativa. Sin embargo sólo el siluriforme Trichomycterus areolatus se encuentra en altas abundancias todo el año, siendo la especie dominante de estos ambientes fluviales artificiales. Entre los factores que pueden dar cuenta de su éxito relativo dentro de los canales están sus hábitos bentónicos y adaptación a ambientes ritrales, una oferta de recursos tróficos concordante con sus hábitos alimentarios y una menor abundancia de depredadores. En este estudio se analiza comparativamente la ecología trófica de esta especie en 174 individuos que habitan en el río Itata (Octava Región de Chile) y 231 de canales de riego que nacen de este sistema fluvial. Además se analizan las relaciones de talla-peso y frecuencia estacional de estados reproductivos, con el fin de inferir acerca del estado de las poblaciones y su condición de residentes en canales de riego. La dieta de las poblaciones de canales incluye una mayor riqueza de táxones y una mayor cantidad de presas consumidas respecto a las del curso natural. El análisis de selectividad muestra que T. areolatus prefiere, tanto en el río como en los canales de riego,presas tales como Chironomidae, Baetidae, Elmidae, Plecoptera y Hyallela. Además, en los canales de riego prefiere presas de mayor biomasa como los lumbricúlidos. Si bien las poblaciones locales de canales presentan, al igual que los ejemplares de río, un crecimiento de tipo isométrico, éstos alcanzan mayores tallas y pesos corporales que los individuos de los cauces naturales. De acuerdo al análisis de estados reproductivos de 345 ejemplares en diferentes períodos del año, las poblaciones de ambientes de canal se reproducen sincrónicamente con las del río, aunque con un leve retardo en la actividad reproductivaTrophic ecology and reproductive aspects of Trichomycterus areolatus (Pisces, Trichomycteridae) in irrigation canal environments. Twelve of the sixteen species of fishes present in the Itata river basin enter the irrigation canals at least once a year, constituting a habitat that is frequently utilized by the native fish assemblages. However, only Trichomycterus areolatus, a native siluriform, is found in great number throughout the entire year, being the dominant species of such artificial environments. Among the factors that could explain the relative success of T. areolatus are its benthonic habits, adaptation to rithral habitat, an offer of trophic resources that is in line with its feeding habits, and a lower abundance of predators in the canals. In this study, the trophic ecology of this species in 174 individuals inhabiting the Itata river (Octava Región, Chile) and 231 from irrigation canals that arise from this river are analyzed and compared. In addition, the length-weight relationship and seasonal frequencies of reproductive status are analyzed, with the purpose of inferring on the status of these populations and their possible condition of resident in these canals. In canals, its diet includes a greater number of different taxa as well as total number of preys consumed in comparison with the river populations, including items of greater biomass, such as lumbriculides. The selectivity analysis showed that T. areolatus prefer prey items like Chironomidae, Baetidae, Elmidae, Plecoptera and Hyallela. Although both the river as well as canal populations show an isometric type growth, they reach greater body lengths and weights in the latter. According to the reproductive states analysis in different periods of the year, populations inhabiting canal environments reproduce synchronically with those of the river, although these latter tend to show a slight delay in the reproductive activity. Rev. Biol. Trop. 53(1-2):195-210. Epub 2005 Jun 24

El sistema fluvial Quilque (orden 3) recibe las descargas de aguas servidas de una población aproximada de 115.000 habitantes y de 19 industrias. Estos residuos se vertían sin tratar directamente al curso del río hasta fines del año 2002, cuando se puso en marcha una planta de tratamiento de aguas servidas. Para analizar los efectos de estas descargas sobre la fauna de peces, se estudió la calidad del agua y estructura comunitaria de la ictiofauna a lo largo de ocho estaciones ubicadas desde aguas arriba de los vertidos hasta 300 m aguas abajo del efluente de la planta de tratamiento. Tanto la calidad del agua como la fauna de peces mostraron una leve mejoría luego de cinco meses de operación de la planta de tratamiento. Aun cuando se redujeron las concentraciones de DBO5, sólidos suspendidos, nitrógeno y coliformes fecales, el río conduce una carga contaminante importante desde aguas arriba y mantiene remanentes en los sedimentos del lecho del río. La ictiofauna se encuentra empobrecida, pero evidencia un proceso de recolonización del sistema, desde las partes altas hacia el tramo inferior que recibía las descargas. Sin embargo, aún se mantienen sectores sin peces, debido a las altas concentraciones de DBO5. Las primeras especies en recolonizar aguas abajo son nativas (Trichomycterus areolatus y Percilia irwini)The Quilque River (3rd order) receives urban wastewater discharge from a population of ca. 115,000 inhabitants and 19 industrial effluents. These residues were discharged without treatment until the end of 2002, when a wastewater treatment plant was constructed. To determine effects of wastewater and industrial effluents on the ichthyofauna, we studied water quality and fish community structure at eight stations distributed from upstream of the areas of the discharge to 300 m downstream of the effluent of the wastewater treatment plant. Both water quality and the fish community showed a slight improvement five months after the treatment plant began operation. Concentrations of BOD5, suspended solids, nitrogen, and fecal coliforms decreased; however, the river contained a significant pollution load from upstream areas, and remnants in the sediments of the riverbed. The fish fauna is impoverished, but there appears to be evidence of a recolonization from upper reaches towards the lower zone receiving the pollution discharges. Areas without fishes still exist due to high concentrations of BOD5. The first species recolonizing the polluted areas are the native fishes Trichomycterus areolatus and Percilia irwini

RESUMEN El estero Nonguén (orden 3), tributario de la zona inferior del río Andalién (región del Bío-Bío), presenta una marcada diferencia entre su parte alta ritral, bien conservada y con un bosque secundario de Nothofagus, y su parte baja potamal, de uso urbano y de aguas con contaminación orgánica. Este contraste podría implicar la alteración de los patrones normales detectados en la ictiofauna chilena descritos para diversos sistemas fluviales. Tales patrones consisten en un aumento del número de especies, individuos y diversidad en el sentido de la corriente, así como en un incremento de las tallas corporales de los individuos que habitan las zonas bajas. Se estudió la composición específica de peces del estero Nonguén y sus patrones comunitarios a lo largo del sistema fluvial en un ciclo anual. Se encontró un incremento en la riqueza específica, desde cuatro especies en el ritrón a diez en el sector de desembocadura. Tanto la diversidad, abundancia y distribución de los peces varió según la época del año, reflejando los desplazamientos asociados a la ontogenia, reproducción y alimentación de la fauna íctica. Las estaciones de la zona media y baja del estero presentaron un ensamble con individuos de menor tamaño que los que se encuentran en la cabecera, consistentemente con la dominancia de salmónidos de mayor talla en la parte alta. Los resultados sugieren que: (i) la alteración del área potamal no modifica significativamente los patrones característicos de la ictiofauna de sistemas fluviales, y que (ii) el estero Nonguén es un sistema de reproducción y crianza de juveniles de especies nativas e introducidas, las cuales conforman asociaciones permanentes en este sistema fluvial.ABSTRACT The Nonguén stream (order 3) is a lower zone tributary of the Andalién river coastal mountain basin (Bio-Bío region) which displays a marked difference between its rithral sector (well-conserved and with a secondary Nothofagus forest) and its potamal area (urbanly-used and organically polluted waters). This contrast could imply an alteration in the normal pattern of Chilean ichthyofauna, as described for a variety of fluvial systems in the country: a downstream increase in numbers of species, individuals, and diversity downstream, as well as increased corporal sizes of individuals in the lower zones of the river. Species composition of fishes of the Nonguén stream and their community patterns along the fluvial system within an annual cycle have been studied. The results show a high number of species in the lower parts, i.e. four species in the rithron and ten in the river mouth. The diversity, abundance and distribution of the fishes varied according to the season of the year, reflecting displacements associated with the fauna's ontogeny, reproduction and feeding. The sampling stations of the middle and lower zones of the river presented an assemblage with smaller individuals than those found at the head of the river, with the consistent dominance of larger salmonidae in the upper zone. Accordingly, it is suggested that: (i) the alteration of the potamal area does not significantly modify the characteristic patterns of ichthyofauna in fluvial systems, and (ii) the Nonguén stream is a reproduction and growth system for juveniles of both native and introduced species which make up permanent associations in the fluvial system.

Con el objetivo de conservar la fauna íctica nativa y como medida de mitigación al impacto generado por la interrupción del libre desplazamiento de peces en el río Laja (Región del Biobio), se llevó a cabo un programa de translocación de peces nativos. Entre los años 1997 y 2000 se estudió la composición y estructura comunitaria y poblacional de la ictiofauna del área, determinando la necesidad de transferir ejemplares de tres especies nativas con problemas de conservación: Diplomystes nahuelbutaensis, Trichomycterus areolatus y Percilia irwini. La campaña de translocación se llevó a cabo en enero de 2001, capturando un total de 1835 ejemplares, de los cuales 1.653 se reubicaron vivos. La sobrevivencia obtenida en las tres especies fue alta durante las tres etapas de la campaña (toma de datos, mantención y traslado), siendo superior al 90% en cada una de ellas. Se capturaron 852 ejemplares de P. irwini y se translocaron 760; 643 individuos de T. areolatus, de los cuales se reubicaron 591 y 340 de D. nahuelbutaensis, de los que se transfirieron 302. En las tres especies la mayor mortalidad ocurrió en los estados juveniles. Tanto T. areolatus como P. irwini, presentaron mayor mortalidad durante la toma de datos (peso y longitud), en tanto que D. nahuelbutaensis resultó más sensible al traslado. En todos los casos esta mortalidad por etapa fue inferior al 7%. Para aumentar la eficiencia de esta estrategia de conservación se sugiere: (a) evitar la extracción de ejemplares juveniles, (b) eliminar la etapa de toma de datos de cada individuo capturado (c) reducir el tiempo de mantención de los peces en recipientes aireados, y (d) transportar los ejemplares en bajas densidades por contenedorIn order to conserve the native ichthyofauna and as mitigation procedure to prevent the impact generated by the interruption of the free displacement of fish in the Laja river (Biobio Region), a translocation program for native fish was carried out. Between the years 1997 and 2000 the species composition, communitary and population structure of the ichthyofauna were studied, determining the need to transfer individuals of three native species with conservation problems: Diplomystes nahuelbutaensis, Trichomycterus areolatus and Percilia irwini. The translocation campaign was carried out in January of the 2001, capturing a total of 1835 fishes, of which 1653 was restocking. The number of survivals of the three species was high during the three phases of the campaign, being upper 90% in each one of them. 852 P. irwini were captured and 760 restocked; 643 T. areolatus were captured and 591 restocked, and 340 D. nahuelbutaensis were captured and 302 restocked. In the three species the highest mortality occurred in the juveniles. T. areolatus and P. irwini showed greater mortality during data recording (weight and body length), while D. nahuelbutaensis resulted more sensitive to the transfer. In all the cases, this mortality was lower to 7%. To enlarge the efficiency of this strategy of conservation we suggested: (a) to avoid the juvenile extractions, (b) to eliminate the phase of taking data of each specimen captured, (c) to reduce the time of fish stored in containers, and (d) to transport the fishes in low densities