Artificial Stream Research Articles

The impacts of increasing current velocity on the drift of Simulium monticola (Diptera: Simuliidae): a laboratory approach

Current velocity and associated physical forces are among the most important factors shaping lotic benthic communities. The recent increase in the frequency and intensity of flow alterations, especially related to hydroelectric use or irrigation, represents a key element of riverine environment deterioration. Numerous studies have investigated the effect of current velocity increases on macrobenthic fauna, underlining that, in most cases, these increases enhance the drift, i.e. the abandonment of the substrate by macroinvertebrates. The purpose of this study is to examine the drift propensity of Simulium monticola (Diptera: Simuliidae) under different water velocities. Simuliidae are one of the most characteristic components of fast-flowing environments in rivers. Experiments were conducted in an artificial stream in the laboratories of Politecnico di Torino, analysing the drift of organisms at different current velocities. The observed variability of drift appears to be related to velocity increases: interestingly, we evidenced an inverse relationship between velocity and drift propensity, with low amounts of drifting organisms at higher velocities. This tendency was not related to the size of Simuliidae larvae: when comparing the size of drifting organisms with velocity, no significant correlations were detected. We hypothesized that the tendency to drift was mainly behavioural rather than catastrophic, and related to the preference for high water velocities. Our findings support the hypothesis that increases in water velocity can cause complex changes in the drift of the macrobenthic community, increasing the propensity for some species to leave the substrate and decreasing it for others.

Invasive rainbow trout affect habitat use, feeding efficiency, and spatial organization of warpaint shiners

Rainbow trout have been introduced to six of the seven continents and currently are widely stocked for sport fishing. Despite their broad distribution, outside of New Zealand, little is known about the effects of rainbow trout on native species, especially fishes. We conducted experiments in an artificial stream to assess hypotheses that stocked rainbow trout significantly affected: (1) mesohabitat use, (2) foraging success, (3) social behavior, and (4) spatial organization of warpaint shiners (Luxilus coccogenis) a common native minnow found in southern Appalachian streams, with similar patterns of microhabitat use to rainbow trout. We replicated experiments at high and low natural densities (two and five warpaint shiners) and spring/fall (12 °C) and summer (17 °C) temperatures. Treatments included: (1) a control (five warpaint shiners), (2) trout (five warpaint shiners and one rainbow trout), (3) large fish control (five warpaint shiners and one river chub) and (4) density control (six warpaint shiners). The presence of rainbow trout produced a shift by warpaint shiners from pool mesohabitats to shallower, higher velocity habitats with more variable substrata, as well as reduced prey capture success, feeding efficiency, and distance from the front of the tank (i.e., warpaint shiners moved closer to food release points), and increased the distance to the additional fish (i.e., avoidance of the rainbow trout). Negative effects on foraging behaviors were stronger in 12 °C treatments. In a realistic stream flume the presence of rainbow trout produced effects that likely influenced individual fitness of warpaint shiners. The potential effects of stocking rainbow trout on native non-game fishes, such as warpaint shiners should be assessed when implementing or evaluating stocking programs.

Behavioural response of Kootenai white sturgeon (Acipenser transmontanus, Richardson, 1836) early life stages to gravel, pebble, and rubble substrates: guidelines for rearing substrate size

Summary Guidelines for creating rearing substrate for sturgeon early life stages are needed for restoration programmes creating habitats for spawning and rearing of early life stages. To determine the effects of rock size on motile early life stages, experiments were conducted in artificial streams to observe the behaviour of free embryos and larvae of Kootenai River white sturgeon (Acipenser transmontanus) relative to rock size. Most (�90%) of the free embryos in replicate test streams with 100% gravel, 100% pebble, or 100% rubble hid under rocks, with few moving downstream. There was no difference in downstream movement of free embryos among rock treatments, therefore all rock types provided cover habitat. Similarly, in rock mixture tests, with a variable percentage of pebble, small rubble, or large rubble in different tanks, even fewer free embryos moved downstream. With increasing age, larvae increasingly used the open bottom and velocity refuges downstream of or alongside rocks of any size while drift feeding. Downstream movement of larvae in both rock regime tests was affected by rock size, with significantly reduced movement relative to increasing abundance of large rock (rubble). However, in all rock mixtures, free embryos (and later, larvae when they stopped dispersing) preferred the smallest rock size available (pebble; P = 0.0001). This suggests a strong innate preference of both life stages for small substrate that is likely related to increased survival. A rock mixture of 10% gravel (16–32 mm diameter) and 30–40% pebble (diameter, 30–60 mm) should provide adequate rearing substrate for free embryos and early-larvae. The remaining 50–60% should be mixed rubble and boulders for spawning and egg rearing.

Comparing competitive ability and associated metabolic traits between a resident and migratory population of bull trout against a non-native species

Juvenile bull trout Salvelinus confluentus from two geographically and ecologically distinct popu- lations were compared with regard to their ability to compete with non-native brook troutSalvelinus fontinalis in an artificial stream, and with respect to their rates of oxygen consumption. Bull trout collected from a migra- tory population foraged more successfully against brook trout competitors than those from a resident population, capturing more of a limited amount of food items presented. The migratory population was also more ag- gressive (measured by the number of nips, chases and lateral threat displays) against brook trout competitors than the resident population. Bull trout from the migra- tory population had a higher oxygen consumption rate (203 mg O2 kg · hr -1 ) in the field than similar sized fish from the resident population (183 mg O2kg · hr -1 ). These results suggest native bull trout have population-level variation in competitive ability against a non-native spe- cies and such competitive ability is positively associated with metabolism and migratory life history.

Olfactory Homing of Chum Salmon to Stable Compositions of Amino Acids in Natal Stream Water

Many attempts have been made to identify natal stream odors for salmon olfactory homing. It has recently been hypothesized that odors are dissolved free amino acids; however, it is unknown whether these odors change on a seasonal or annual basis. We analyzed dissolved free amino acid (DFAA) concentration and composition of water from the Teshio River in Hokkaido, Japan, where chum salmon (Oncorhynchus keta) returned for spawning, during juvenile downstream migration in spring and adult upstream migration in autumn with a 4-year difference. Among the 19 amino acids found in the Teshio River water, DFAA concentrations fluctuated largely, but 5-7 stable DFAA compositions (mole %) were found between the spring and autumn samples over a 4-year span. Two kinds of artificial stream water (ASW) were prepared using the same DFAA concentration in the Teshio River during the time of juvenile imprinting in spring (jASW) and adult homing in autumn (aASW), after a 4-year period. In behavioral experiments of upstream selective movement in a 2choice test tank, 4-year-old mature male chum salmon captured in the Teshio River showed significant preference for either jASW or aASW when compared to control water, but did not show any preference with respect to jASW or aASW. In electro-olfactogram experiments, adults were able to discriminate between jASW and aASW. Our findings demonstrate that the long-term stability of the DFAA compositions in natal streams may be crucial for olfactory homing in chum salmon.

다목적 여과저류지를 이용한 하천수의 조류와 인 제거방안 제안

Abstract : In an effort to find a solution to the eutrophication of major Korean rivers, a method to utilize multi-purpose filtration pond was investigated. As literature showed that oyster shell is known to be the most adequate for the removal of dissolved phos-phorus in Korean rivers, batch and column experiments were performed using oyster shell as an adsorbent in this study. The results of the batch experiment showed that the removal of dissolved phosphorus from river water through adsorption as a way of preventing algal growth was not practical. The results obtained from the column experiment, however, suggested that oyster shell may be utilized as an adsorbent under limited conditions. Based on the results of the experiments a methodology was proposed to remove algae from river water through the use of multi-purpose filtration pond. This method involves mechanically removing the accumu-lated algae cake from the surface of the artificial stream in the pond towards the condensing part located at the lower reach of the stream, where particles gather before the final removal. In addition, employment of oyster shell as an adsorbent in the condensing part allows prevention of phosphorus released from the dead algae re-entering the river water.

다목적 여과저류지에서 여과수의 산출율과 수질개선도에 관한 실험연구

Abstract : A pilot-scale test-bed was operated employing three soils with different grain sizes dredged from the Nakdong River to obtain the design and operation parameters of the multi-purpose filtration pond, such as the filtrate productivity of the filter sand, the appropriate removal period of the surface clogging and the contaminant removal efficiency. The cross-flow velocities were applied stepwise ranging from 0 to 40 cm/sec in order to simulate the various velocities in the artificial stream of the pond. Results showed that a filtrate production rate of 5~3 m 3 /m 2 -day was maintained by removing the surface clogging every 7 to 13 days and that the filtrate quality was not affected by the factors of the filtrate production rate, the grain size of the filter sand and the cross-flow velocity. Results also showed that most of the removal occurred within 50 cm of the top soil and that the removal efficiencies with the filtration distance of 2.4 m were 80~95% for turbidity, 20~30% for COD, 75~90% for BOD, 5~20% for total nitrogen and 20~60% for total phosphorus, which suggested that particulate matters had a high removal efficiency.

Triclosan Exposure Increases Triclosan Resistance and Influences Taxonomic Composition of Benthic Bacterial Communities

Triclosan (TCS) is a broad-spectrum antimicrobial compound that is incorporated into numerous consumer products. TCS has been detected in aquatic ecosystems across the U.S., raising concern about its potential ecological effects. We conducted a field survey and an artificial stream experiment to assess effects of TCS on benthic bacterial communities. Field sampling indicated that TCS concentrations in stream sediments increased with degree of urbanization. There was significant correlation between sediment TCS concentration and the proportion of cultivable benthic bacteria that were resistant to TCS, demonstrating that the levels of TCS present in these streams was affecting the native communities. An artificial stream experiment confirmed that TCS exposure could trigger increases in TCS resistance within cultivable benthic bacteria, and pyrosequencing analysis indicated that TCS resulted in decreased benthic bacterial diversity and shifts in bacterial community composition. One notable change was a 6-fold increase in the relative abundance of cyanobacterial sequences and a dramatic die-off of algae within the artificial streams. Selection of cyanobacteria over algae could have significant implications for higher trophic levels within streams. Finally, there were no observed effects of TCS on bacterial abundance or respiration rates, suggesting that bacterial density and function were highly resilient to TCS exposure.

Nutrient enrichment of a heterotrophic stream alters leaf litter nutritional quality and shredder physiological condition via the microbial pathway

Streams receiving agricultural runoff are typically enriched with nutrients, which variously impact stream communities. We examined the effects of phosphate and nitrate enrichment on leaf litter breakdown, microbial biomass and the nutrition of an invertebrate shredder to determine how nutrients are transferred through the stream detrital food web. Using artificial streams, individuals of Anisocentropus kirramus (Trichoptera: Calamoceratidae) were fed leaves of Apodytes brachystylus (Icacinaceae) under different nutrient regimes. We measured the amount of leaf material consumed or decomposed and the microbial biomass colonising the leaves. The dry mass, and protein, lipid and carbohydrate composition of A. kirramus larvae were determined after 28-day feeding on the leaves. Supplements of phosphorus, but not nitrogen, enhanced leaf breakdown, microbial growth and growth of larvae. Microbial biomass and dry mass of larvae increased with nutrient enrichment and they were significantly correlated. Thus, the phosphorus supplement was transmitted through the detrital food web via the microbial pathway, resulting in higher nutritional quality of leaves and enhanced physiological condition of the shredder. Understanding such subtle relationships is important in determining the impacts of anthropogenic contaminants on freshwater ecosystems.

Can nutrients mask community responses to insecticide mixtures?

The ecological effect of simultaneous exposure to two nutrient gradients, three insecticides and different predator intensities was investigated over a 3-week period in 80 outdoor, artificial streams using field-collected benthic invertebrates. The experimental design consisted of a 2 × 5 factorial structure with two nutrient levels (oligotrophic or mesotrophic) and five concentrations of the ternary insecticide mixture consisting of the insecticides (chlorpyrifos, dimethoate and imidacloprid). Equivalent toxic unit doses were summed to create a ternary insecticide dose (e.g., 0.1 + 0.1 + 0.1 = 0.3 TU) resulting in a range of ternary insecticide mixture toxicity (i.e., control groundwater, 0.3, 0.6, 0.9 and 1.2 TU). Two genera of insect predators, Gomphus spp. (Odonata) and Agnetina spp. (Plecoptera) were also added into each replicate stream, at densities and sizes comparable to those found at our collection site, to evaluate how the contribution of predators may change in nutrient limited (oligotrophic) versus amended (mesotrophic) systems. We describe a causal mechanism whereby the combined action of nutrients and insecticides reshaped aquatic community structure by interacting through multiple pathways. Specifically, mesotrophic conditions reduced the toxic effects of ternary insecticide mixtures for aquatic insects which, in some cases, appeared to increase abundance of aquatic insects. However, higher levels of insecticides in mesotrophic streams negated this effect and were even more toxic; for example, to aquatic insect grazers than the same insecticide doses in oligotrophic treatment levels. Effects of predators were only significant in oligotrophic streams. Evidence is provided as to how nutrient and contaminant interactions can greatly complicate the assessment of community level responses to insecticide mixtures due to direct and indirect effects of the resulting changes in the density of different genera and functional feeding groups within a community.

Design of a groundwater model to determine the feasibility of extending an artificial salmon-spawning stream: case study for Marx Creek, near Hyder, Alaska

Marx Creek is a groundwater-fed, artificial salmon-spawning stream near Hyder, Alaska. The purpose of this project was to develop a groundwater flow model to predict baseflow to a proposed 450-m extension of Marx Creek. To accomplish this purpose, water levels were monitored in 20 monitor wells and discharge measurements were recorded from Marx Creek. These data were used to create a three-dimensional groundwater flow model using Visual MODFLOW. Three predictive simulations were run after the model was calibrated to groundwater levels and stream discharge measurements. The proposed extension was added to the calibrated model during the first simulation, resulting in simulated baseflow to the extension stream exceeding simulated baseflow to the existing Marx Creek by 39 %. Sections of Marx Creek were removed from the model during the second simulation, resulting in a 5 % increase in simulated baseflow to the extension stream. A 32-cm reduction in the water table was simulated during the third simulation, resulting in an 18 % decrease in simulated baseflow to the extension stream. These modeling results were used by Tongass National Forest personnel to determine that baseflow to the proposed extension would likely be sufficient to provide habitat conducive to salmon spawning. The extension stream was constructed and portions of Marx Creek were decommissioned during the summer of 2008. It was observed that there is comparable or greater discharge in the extension stream than there was in the decommissioned sections of Marx Creek, although neither discharge nor stream stage measurements have yet been collected.

Online fuzzy medoid based clustering algorithms

This paper describes two new online fuzzy clustering algorithms based on medoids. These algorithms have been developed to deal with either very large datasets that do not fit in main memory or data streams in which data are produced continuously. The innovative aspect of our approach is the combination of fuzzy methods, which are well adapted to outliers and overlapping clusters, with medoids and the introduction of a decay mechanism to adapt more effectively to changes over time in the data streams. The use of medoids instead of means allows to deal with non-numerical data (e.g. sequences…) and improves the interpretability of the cluster centers. Experiments conducted on artificial and real datasets show that our new algorithms are competitive with state-of-the-art clustering algorithms in terms of purity of the partition, F1 score and computation times. Finally, experiments conducted on artificial data streams show the benefit of our decay mechanism in the case of evolving distributions.

See it with my eyes: artificial stream research communicated by an artist

Abstract Artist Anne Rinn takes the reader on an excursion to an indoor and outdoor artificial pond and stream mesocosm system. This device was constructed and put into operation in 2001 in order to carry out scientific investigations concerning the aquatic environment, with the main focus on fate and effects of pollutants. Both technical features of the facility and the work and ideas for scientists and technicians were translated by her into an art exhibition which also included a film. This report on the project consists of two different text parts, one by the third author, who is an aquatic toxicologist, and one by the second author, an art historian. Their different backgrounds are reflected in different thinking and styles of expression. The text is rounded off by the photos of the first author, the artist.

Effects of substrate and water velocity on migration by early-life stages of kaluga, Huso dauricus (Georgi, 1775): an artificial stream study

Summary The effect of two environmental factors (substrate type and water velocity regime) was studied in the ontogenetic migration intensity of kaluga, Huso dauricus, a protected species in the Amur River. Early-life stages studied were: free embryos = days 0–8; larvae = days 9–49; and juveniles = days 50–66. Effect of treatments on fish migration intensity was observed in circular channels, allowing migration in an endless stream. Daily migration intensity of fish was characterized by counting the number of daily upstream or downstream fish passes past a specific site in the channel observed for 5 min every hour by vision or video camera. The hypothesis that substrate type (bare bottom or sand-small cobble) affects migration intensity was accepted, depending on the life stage. For example, the substrate type had no effect on migration intensity of days 0–6 free embryos. However, the intensity in days 7–8 free embryos and days 9–29 larvae was greater over rock substrate, while intensity in days 46–49 larvae and days 50–66 juveniles was greater when the bottom was bare. Thus, the effect of the substrate on migration varied in intensity according to the life stage, and within the larva life stage, by age. The velocity regime had a positive effect on migration intensity of free embryos, but a high velocity (mean, 29.9 cm∙s−1) delayed the resting period of day 8 free embryos and day 9–15 larvae. Free embryos and larvae in low vs fast velocities showed that they may have a drive to migrate a similar distance, and moreover, that a triggering velocity may be needed to initiate or to stop migration. The hypothesis was accepted that the rearing velocity affects migration intensity, e.g. larvae reared in still water and then placed in moving water had a compensatory migration intensity response. For population enhancement stocking of H. dauricus, the results indicate culture practices must insure that: (i) same-population individuals are mated to produce early-life stages with the correct behaviour, (ii) migrating larvae, not juveniles, should be stocked, and (iii) larvae should be released in a river reach with a bottom velocity ≥30 cm∙s−1 containing sand and small pebbles.

Visual speech segmentation: using facial cues to locate word boundaries in continuous speech

Speech is typically a multimodal phenomenon, yet few studies have focused on the exclusive contributions of visual cues to language acquisition. To address this gap, we investigated whether visual prosodic information can facilitate speech segmentation. Previous research has demonstrated that language learners can use lexical stress and pitch cues to segment speech and that learners can extract this information from talking faces. Thus, we created an artificial speech stream that contained minimal segmentation cues and paired it with two synchronous facial displays in which visual prosody was either informative or uninformative for identifying word boundaries. Across three familiarisation conditions (audio stream alone, facial streams alone, and paired audiovisual), learning occurred only when the facial displays were informative to word boundaries, suggesting that facial cues can help learners solve the early challenges of language acquisition.

Current velocity influences the facilitation and removal of algae by stream grazers

The modification of flows in lotic ecosystems can have dramatic effects on abiotic and biotic processes and change the structure of basal trophic levels. In high-gradient streams, most of the biota are benthic, and decreased flow may homogenize and reduce benthic current velocity, potentially changing stream ecosystem function. Grazing by macroinvertebrates is an important component of stream function because grazers regulate energy flow from primary producers to higher trophic levels. We conducted an experiment to examine how macroinvertebrate grazers facilitated or removed algal biomass across a gradient of benthic current velocity (0–40 cm s−1). We chose three grazers (Drunella coloradensis, Cinygmula spp., and Epeorus deceptivus) from a montane stream and conducted our experiment using 24 artificial stream channels that had three treatments: no grazers (control), single-grazer, and combined-grazer treatments. In the absence of grazers, algal biomass increased with benthic current velocity. Grazer treatments differed from the control in that more algal biomass was removed at higher velocities, whereas algal accrual was largely facilitated at low velocities. The transition from facilitation to removal ranged from 4.5 to 5.9 cm s−1 for individual grazer treatments and occurred at 11.7 cm s−1 for the combined-grazer treatment. Our data suggest that velocity plays a significant role in the facilitation and removal of algae by macroinvertebrate grazers. Additionally, the patterns revealed here could have general implications for algal accrual in systems where flow is reduced.

Word frequency, function words and the second gavagai problem

The classic gavagai problem exemplifies the difficulty to identify the referent of a novel word uttered in a foreign language. Here, we consider the reverse problem: identifying the referential part of a label. Assuming “gavagai” indicates a rabbit in a foreign language, it may very well mean “a rabbit” or “that rabbit”. How can a learner know whether rabbit is actually said “vagai”, “gava” or “gavagai”? Here, we report evidence suggesting that infants can identify potential function words on the basis of their high frequency and avoid considering them when associating labels and referents. In three experiments, 17-month-old infants were first exposed to an artificial speech stream where frequent and infrequent syllables alternated (e.g., … gibuvokugifevodegita…). Infants then saw a novel object and heard the repetition of a bisyllabic label consisting of one frequent and one infrequent syllable (e.g., vomu). The frequent syllable was the initial syllable of the label in Experiment 1 and the final in Experiments 2 and 3. We then presented infants with both the previous and now familiar object and a novel object. We asked whether infants would be more likely to orient first towards the familiar object when hearing a label with a new frequent and the previous infrequent syllables (e.g., gimu), or when hearing a label with a new infrequent and the previous frequent syllables (e.g., vona). Results suggest that the infrequent syllable was associated more strongly with the object, than the frequent one, only when the perceived position of the frequent syllable was constant all along the experiment.

The influence of food quantity on metal bioaccumulation and reproduction in fathead minnows (Pimephales promelas) during chronic exposures to a metal mine effluent

Metal mine effluents can impact fish in the receiving environment via both direct effects from exposure as well as indirect effects via food web. The main objective of the present study was to assess whether an indirect effect such as reduced food (prey) availability could influence metal accumulation and reproductive capacity in fish during chronic exposure to a metal mine effluent. Breeding pairs of fathead minnows (Pimephales promelas) were exposed to either reference water (RW) or an environmentally relevant metal mine effluent [45 percent process water effluent (PWE)] for 21 days and fed either low food quantities [LF (a daily ration of 6–10 percent body weight)] or normal food quantities [NF (a daily ration of 20–30 percent body weight)] in artificial stream systems. Fish in RW treatments were fed Chironomus dilutus larvae cultured in RW (Treatments: RW-NF or RW-LF), while fish in PWE treatments were fed C. dilutus larvae cultured in PWE (Treatments: PWE-NF or PWE-LF). Tissue-specific (gill, liver, gonad and carcass) metal accumulation, egg production, and morphometric parameters in fish were analyzed. Fathead minnows that were exposed to LF rations had significantly smaller body, gonad and liver sizes, and were in a relatively poor condition compared to fathead minnows exposed to NF rations, regardless of the treatment water type (RW or PWE) (two-way ANOVA; p<0.05). Although elevated concentrations of copper, nickel, rubidium, selenium, and thallium were recorded in C. dilutus cultured in PWE, only the concentrations of rubidium, selenium and thallium increased in tissues of fish in PWE treatments. Interestingly though, despite the greater abundance of metal-contaminated food in the PWE-NF treatment, tissue metal accumulation pattern were almost similar between the PWE-NF and PWE-LF treatments, except for higher liver barium, cobalt and manganese concentrations in the latter treatment. This indicated that a higher food ration could help reduce the tissue burden of at least some metals and thereby ameliorate the toxicity of metal-mine effluents in fish. More importantly, cumulative egg production in fish was found to be lowest in the PWE-LF treatment, whereas fish egg production in the PWE-NF treatment was not impacted. Overall, these findings suggest that decreased food abundance could have a greater impact than metal accumulation in target tissues on the reproductive capacity of fish inhabiting metal-mine effluent receiving environments.

Interstitial movement and emergence of barbel Barbus barbus free embryos and larvae

The movement of barbel Barbus barbus free embryos in the interstitial zone and the timing of larval emergence were studied for 12 days in an artificial stream. After egg fertilization (day 1), hatching occurred on day 6, downstream interstitial movements of free embryos on day 9 and emergence and downstream movement of all larvae on day 12, with density of free embryos decreasing as day of emergence approached. The results suggest that a memory-based response of B. barbus to environmental conditions, previously observed in 0+ year juveniles, begins at an early age.

Stress hormone responses in ayu Plecoglossus altivelis in reaction to different catching methods: comparisons between electrofishing and cast netting

It is important to select the most appropriate method for fish sampling in streams and rivers; the sampling efficiency as well as any negative effect of the method of fish sampling on fishes such as stress, injury, and mortality must be considered. This study aimed to investigate stress hormone responses in ayu Plecoglossus altivelis in reaction to direct current (DC) electrofishing, alternating current (AC) electrofishing, and cast netting in artificial streams. The mortality, injury rate, and catch efficiency of these catching methods were also compared. It was found that immediately after capture, fish caught using a cast net exhibited significantly higher cortisol levels than did control fish that were caught rapidly by a hand net. Cortisol levels did not differ between electroshocked fish and the controls. Time required to catch 12 fish was shorter when DC was used (20 s) than when AC was used (45 s). The time required to catch fish greatly increased when a cast net was used (840 s). Cortisol levels in DC electroshocked and control treatment groups were at resting levels 24 and 48 h after capture. However, higher cortisol levels were found in fish captured using a cast net at both these time points. Cortisol levels in AC electroshocked fish returned to lower levels at 24 h, but increased again at 48 h. Furthermore, 48 h following capture, the fish caught by AC electrofishing exhibited higher mortality (7.5 %) than those captured by other methods (0 %). Spinal injury was also detected in one of the fish in this group. Considering these findings, DC electrofishing is the most effective and least damaging method for collecting P. altivelis in streams with respect to stress, physical damage, and efficiency.