Juan P. Barriga

Spatial and temporal distribution of landlocked Galaxias maculatus and Galaxias platei (Pisces: Galaxiidae) in a lake in the South American Andes

Abstract Galaxiids are present in many of the Andean lakes in southern South America. We studied landlocked Galaxias maculatus (Jenyns) and Galaxias platei Steindachner populations in a deep oligotrophic lake (Lake Gutiérrez, Patagonia, Argentina). Their temporal and spatial distribution, intralacustrine movements (horizontal and vertical), and spawning periods were analysed using several sampling techniques (ichthyoplankton net, seine net, gill net, and baited benthic taps). We identified the early life stages of both species based on their morphology and otolith shape. The free embryos of both species migrate to the limnetic zone, where they coexist as larvae, facing the same food availability and probably the same predation risk. Each species then moves on to its own juvenile and adult habitat: the littoral and benthic zone for G. maculatus and only the deeper benthic zone for G. platei. Their adult habitats and part of their spawning periods partly overlap.

Distribution of introduced and native fish in Patagonia (Argentina): patterns and changes in fish assemblages

The interaction between native fishes and salmonids introduced in Patagonia at the beginning of the 20th Century, developed at the same time as the environmental change. The phenomenon of global warming has led to the formulation of predictions in relation to changes in the distribution of species, in the latitudinal dimension, both at intralacustrine, or small streams levels. The aim of the present work includes three main objectives: a) to compose a general and updated picture of the latitudinal distribution range of native and alien fishes, b) to analyze the historical changes in the relative abundance of Percichthys trucha, Odontesthes sp., and salmonids in lakes and reservoirs, and c) to relate the diversity and relative abundance of native and salmonid fishes to the environmental variables of lakes and reservoirs. We analysed previous records and an ensemble of data about new locations along the northern border of the Patagonian Province. We compared current data about the relative abundance of native fishes and salmonids in lakes and reservoirs, with previous databases (1984–1987). All samplings considered were performed during spring-summer surveys and include relative abundance, as proportions of salmonids, P. trucha, and Odontesthes sp. For the first time, we found changes in fish assemblages from twenty years back up to the present: a significant decline in the relative abundances of salmonids and an increase of P. trucha. We studied the association between the diversity and relative abundance of native and salmonid fishes and the environmental variables of lakes and reservoirs using Canonical Correspondence Analysis. Relative abundance showed mainly geographical cues and the diversity relied largely on morphometric characteristics. Relative abundance and diversity seem to have a common point in the lake area, included into the PAR concept. Native abundance and alien diversity were negatively related with latitude. Greater native diversity was observed in lakes with high PAR compared with salmonids. Historical changes such as southward dispersion, relative abundance changes, and geographical patterns for relative abundance and diversity are basic concepts needed not only in future research but also in management design for Patagonian fish populations.

Quantifying Predation on Galaxiids and Other Native Organisms by Introduced Rainbow Trout in an Ultraoligotrophic Lake in Northern Patagonia, Argentina: A Bioenergetics Modeling Approach

Abstract Exotic rainbow trout Oncorhynchus mykiss support an economically valuable recreational fishery in Patagonia but also create concern for impacts on native organisms. These concerns are intensified by the possibility of hatchery release programs in this region. We estimated losses of different prey from predation by rainbow trout in Lake Moreno, Rio Negro Province, Argentina, using a bioenergetics model combined with input data from directed sampling on growth, seasonal diet, distribution, and thermal experience. The fish community was sampled seasonally using gill nets, hydroacoustics, and ichthyoplankton nets. Pelagic galaxiid larvae and benthic juvenile and adult small puyen Galaxias maculatus were the most important components of the diet. Bioenergetics simulations showed that over a 6-year life span in the lake (ages 1–7), rainbow trout attained a body mass of 2.3 kg and consumed 74.7 kg of food, of which 20% consisted of galaxiid larvae and 16% consisted of adult small puyen. Based on an esti...

Intraspecific variation in diet, growth, and morphology of landlocked Galaxias maculatus during its larval period: the role of food availability and predation risk

Food availability and predation risk have been shown to affect phenotypes during early life history of fishes. Galaxias maculatus, a small fish widely distributed around the southern hemisphere, clearly exhibits a complex trade-off between feeding and predation avoidance during growth over the larval period. We studied the effect of different environmental variables on diet, growth, mortality, and morphology through field surveys and data revision in the literature for limnetic G. maculatus larvae in five oligotrophic lakes of Patagonia. Both number of food categories and prey ingested by larvae were directly related to zooplankton density. Larval growth rate was related with zooplankton density and temperature. Lakes with high zooplankton densities and low predation risk had larvae with deeper bodies and shorter caudal peduncles, while in lakes with less food and high predation risk larvae were slender with shallower bodies and longer peduncles. Food availability and predation risk seem to operate on the swimming performance of G. maculatus larvae through the slenderness of the body and the length of the caudal peduncle. The observed phenotypic variation in growth and morphology could be a key feature that has allowed this species to successfully colonize a wide variety of environments in the southern hemisphere.

Phylogeography of the catfish Hatcheria macraei reveals a negligible role of drainage divides in structuring populations

Southern South America provides a set of unusual geographic features that make it particularly interesting for studying phylogeography. The Andes Mountains run along a north‐to‐south axis and act as a barrier to gene flow for much of the biota of this region, with southern portions experiencing extensive historical glaciation. Geological data reveal a series of drainage reversals, shifting from Pacific Ocean outlets to Atlantic Ocean outlets because of glacier formation that dammed and reversed rivers. Once glaciers melted around 13 000 years ago, drainages returned to the Pacific Ocean. This geologic history predicts that aquatic organisms in Pacific rivers should have their closest relationships to their counterparts in Atlantic rivers immediately to their east. We tested this prediction in the trichomycterid catfish Hatcheria macraei from 38 locations using the mitochondrial cytochrome b gene. Our results show that most populations found in Pacific rivers were closely related to fish found in the adjacent Atlantic draining Río Chubut. Surprisingly, one documented drainage reversal (from Río Deseado into Río Baker) did not result in movement of H. macraei. Overall, we found the lowest levels of genetic structure between most Pacific rivers that are adjacent to the Atlantic draining Río Chubut. We also found low levels of population structuring among three of four contemporary river basins that drain to the Atlantic Ocean. Our findings suggest that drainage basin boundaries have historically not played an important long‐term role in structuring between nine of 11 drainages, an unusual finding in freshwater biogeography.

Freshwater fishes of Patagonia: conservation and fisheries

The absence of much literature on the Patagonian fish fauna in comparison with that of the neotropics, has previously been blamed on its poor species diversity. Knowledge of the fishes of Patagonia, however, rose sharply at the beginning of the present century, allowing for an understanding of the complex biogeographical history that has led to the present diversity and distribution patterns. There are several new and potential threats to biodiversity and conservation of Patagonian fishes, such as the introduction of exotic species, damming, climate change and changes geared to safeguard economic interests, often acting synergistically. A great amount of new information is now available and the aim of the present review is to articulate this knowledge in a comprehensive way in order to aid in the development of tools to face the increasing challenges posed by environmental change and human activity. Knowledge about fishes of Patagonia has grown at the same time as human actions, and presence.

Variation in vertebral number and its morphological implication in Galaxias platei.

Variation in the vertebral number of the puyen grande Galaxias platei was examined for specimens from 22 localities that span the entire distribution range of the species (from 40° to 55° S). The mean vertebral number (NMW ) increases towards high latitudes, i.e. Jordans rule is applicable to this species. Owing to the wide geographic variation of the species, not only in latitude but also in altitude, the most explicative variable for NMW was mean winter air temperature, showing negative dependence. Morphological data suggest that the increment in vertebral number lies in the pre-pelvic region of the trunk and in the caudal region, but not in the segment between pelvic-fin insertion and the origin of the anal fin. As these alterations in body shape have important consequences for hydrodynamics and swimming performance, vertebral number variation in G. platei also holds implications for both individual and population fitness.

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.

Reproductive strategy of the Patagonian catfish Hatcheria macraei

This study describes the reproductive strategy of the stream-dwelling catfish Hatcheria macraei in the Pichileufu River, Argentina. Gonad maturity phases, classified on the basis of histological analysis, stages of gamete development and the frequency distribution of oocyte size, were correlated with macroscopic features of the gonads. Hatcheria macraei has a cystovarian ovary, asynchronous oocyte development and lobular testes. Five oocyte and four spermatogenic stages were identified and related to macroscopic gonad characteristics, making it possible to divide gonad development into five phases for females and males. Mature oocyte diameter ranged from 922 to 1935 µm. Absolute fecundity in mature females varied from 115 to 480 oocytes. Hatcheria macraei has multiple spawning during a protracted reproductive season that extends from December to April. This, together with its small size, is characteristic of an opportunistic reproductive strategy, commonly found in species that inhabit adverse and unpredictable environments, such as the low-order rivers of Patagonia.

Diel locomotor activity and shelter use in the Patagonian catfish Hatcheria macraei under experimental conditions

Abstract Diel locomotor activity and shelter use was experimentally evaluated in Hatcheria macraei under three different light regimens: natural and inverted photoperiods, and during constant darkness. The results demonstrate clear nocturnal activity and highlight the negative phototactic behaviour of H. macraei, proving that light is the external factor that triggers the seeking of shelter and the subsequent hiding action. Locomotor activity was maximal in darkness, intermediate at dawn and dusk, and minimal (maximum shelter use) in full light. During free-running experiments (i.e. constant darkness) H. macraei continued to exhibit the same diel pattern of resting (or hiding) and swimming as under natural light conditions. Nocturnal activity and negative phototactic behaviour appear to be important mechanisms which have enabled H. macraei to withstand the effects of salmonid introduction in lotic environments where other native fishes have suffered negative effects.