Brown Trout Salmo Trutta Research Articles

Impacts of reduced Lepidurus arcticus availability on brown trout life history traits in a mountain reservoir

Lepidurus arcticus (the Arctic tadpole shrimp) is a vulnerable keystone species in Arctic and alpine water bodies where its occurrence and population size may influence the viability and life history traits of resident salmonids. Using data from a Norwegian mountain hydropower reservoir, Aursjoen, we illustrate how reduced availability of L. arcticus as prey resulted in the reduced condition, growth and delayed maturation of resident brown trout (Salmo trutta). We further link changes in the relative abundance of L. arcticus as prey to changing reservoir conditions, e.g. water level changes in the spring period, thereby establishing an indirect link between reservoir operation regimes and brown trout population traits. While no evidence for decreased brown trout survival was found, the results indicate that alternative brown trout prey resources, i.e. the small chydorid cladoceran Eurycercus lamellatus, do not appear to have successfully offset the caloric loss from reduced consumption of large-sized L. arcticus. Although the fundamental explanation for the observed L. arcticus collapse remains largely unknown, the present findings provide strong evidence that this vulnerable crustacean species can affect the abundance, viability and life history traits of valued resident salmonid populations in oligotrophic alpine lakes and reservoirs exposed to climate- and hydropower-driven changes in water levels and temperature.

From a research study to a conservation partnership: Developing approaches to restoring common scoter populations

Abstract Like many sea‐duck populations, the British breeding population of common scoters Melanitta nigra has declined markedly. In 2009, a study was established to measure factors affecting lake use by breeding scoters, to inform conservation measures. That study, published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) in 2016, showed that lakes used by scoters had relatively more shallow water and large invertebrates. Furthermore, lakes with abundant large invertebrates had relatively few brown trout Salmo trutta. These results probably reflect the importance of foraging habitat (shallow water), prey abundance (large invertebrates), and competition for prey (trout abundance) in influencing scoter lake use. To develop this study, additional research, and scoter conservation measures, we formed a long‐term partnership, comprising nature conservation non‐governmental organizations, statutory agencies, fisheries managers and the regional hydropower company. The partnership meets regularly to coordinate and review research and develop conservation measures, building on the earlier lake‐use study. At key scoter lakes managed for hydropower, the partnership negotiated a revised water level management regime, favouring shallow water availability in the breeding season. This regime was informed by additional research, showing the value of certain islands for nesting scoters, and water level requirements to maintain these as islands. In a different key scoter area — an extensive near‐natural peatland where recreational angling takes place — the partnership established a trial of increased brown trout angling, with increased fish removal, to determine whether this would increase invertebrate prey abundance and benefit breeding scoters. Both conservation interventions are currently being evaluated by detailed monitoring. Overall, the earlier study published in AQC, was important in strengthening and informing our researcher–practitioner partnership, as we collaborated within an adaptive management framework to reverse scoter declines. Long‐term interdisciplinary partnerships are likely to have an important role to play in general, for the successful conservation of aquatic biodiversity.

Microplastics in brown trout (Salmo trutta Linnaeus, 1758) from an Irish riverine system

Rivers play an important role in the overall transport of microplastic pollution (1 μm to 5 mm), with fluvial dynamics expected to influence biotic interactions, particularly for fish. So far, there have been few assessments of microplastics in freshwater salmonids. The prevalence (i.e. percentage occurrence) and burden (i.e. abundance per fish) of microplastics were assessed in the gastrointestinal tracts (GITs) and stomach contents (SCs) of 58 brown trout Salmo trutta Linnaeus, 1758 sampled at six sites along the River Slaney catchment in south-east Ireland. Sites were divided into two classifications (high and low exposure) based on proximity to microplastic pollution sources, comprising three sites each. Analysis of biological traits (e.g. fish length) and diet was performed on the same fish to determine possible factors explaining microplastic burden. Microplastics were found in 72% of fish having been recovered from 66% of GITs (1.88 ± 1.53 MPs fish⁻1) and 28% of SCs (1.31 ± 0.48 MPs fish⁻1). Fibres were the dominant particle type recovered from GITs (67%) and SCs (57%) followed by fragments. No difference in median microplastic burden was observed between fish collected in high and low exposure sites. Microplastic burden was unrelated to fish fork length, while microplastic size distribution (100 ≤ 350 μm, 350 μm to ≤ 5 mm) was unrelated to S. trutta age class estimates. Furthermore, microplastic burden was not explained by dietary intake. Though further research is necessary, this study showed the presence of microplastics in wild S. trutta collected from an Irish riverine system, which could have further implications for top-level consumers that feed on the species, including humans. Further analysis is required to determine possible trophic linkages for the species, with respect to microplastics, and to assess the suitability of S. trutta for monitoring microplastics in river systems.

Mysterious syndrome causing high mortality in wild brown trout in Eastern Switzerland, pathology and search for a possible cause.

Since 2016, annually occurring species-specific die-offs of brown trout (Salmo trutta fario) occurred in the Thur River, situated in the Eastern part of Switzerland. These events lead to drastically reduced population densities in the impacted river regions. Clinical signs in brown trout and mortality were restricted to few weeks in August/September. To characterize the syndrome and to find possible causes, from end of March to November 2018, one-year-old brown trout (Salmo trutta fario) and rainbow trout (Oncorhynchus mykiss) were exposed to water from Thur River, fish were sampled regularly and screened for infectious agents, including viral metagenomics, and pathology was described. Starting approximately four months post-exposure, brown trout showed severe lymphohistiocytic pancarditis and necrotizing and haemorrhagic hepatitis. These lesions were recorded until the end of the experiment in November. Rainbow trout were not affected at any point in time. No infectious agents could be identified so far as cause of disease, especially no viral aetiology. Even if pathogenesis and pathology point in the direction of an infectious agent, a causative relationship could not be confirmed and aetiology remains unclear.

Specific Features of the Ultrastructure of Mesonephros of Smolts of the Atlantic Salmon Salmo salar L. (Baltic Sea population) and Brown Trout Salmo trutta L.

The ultrastructure of the mesonephros of the natural population of Atlantic salmon smolts (Salmo salar L., 1758) and brown trout smolts (Salmo trutta L., 1758) inhabiting the Luga River in Leningrad oblast, Russia, was studied. The general plan of the mesonephric kidney structure is presented. Specific features of the structure of leukocytes and nephron of salmonids under smoltification are described. The size of leukocytes and the height of the epithelial cells of the proximal tubules of the kidneys of salmon smolts are greater in comparison with those kidney cells of freshwater teleost fishes. The number, size, and population density of mitochondria, as well as the development of a rough and smooth endoplasmic reticulum in different types of cells of the mesonephros of salmon smolts, are higher than those in freshwater fish. A similar pattern is observed for the number of vesicles in the basal part of the distal tubule of the kidneys of the salmon smolt in comparison with freshwater fish. Cells with radially arranged vesicles (CRAVs) of different ultrastructures have been found for the first time in mesonephros of Atlantic salmon. All the described features of the ultrastructure of mesonephros cells are revealed for the smolts prior their migration into sea water.

Anthropogenic and natural size-related selection act in concert during brown trout (Salmo trutta) smolt river descent

By hindering migration and inducing direct turbine mortality during downstream migration, hydropower is regarded as one of the most serious threats to anadromous salmonids. Yet, little attention has been paid to long-term turbine-induced selection mechanisms effecting fish populations. This work evaluates turbine and post-turbine survival of PIT-tagged wild brown trout smolts. By estimating individual river and sea survival rates, we were able to compare survival rates of smolts that had migrated through the turbine with smolts that had bypassed the turbine, as well as investigate both natural and anthropogenic size-selective mechanisms operative on the population. Total river-descent survival probability was 0.20 for turbine migrants and 0.44 for bypass migrants. The surviving turbine migrants were significantly smaller than their bypass counterparts and more exposed to predation from Northern pike. The estimated mean-adjusted selection gradient was − 0.76 for turbine migrants and + 1.85 for the bypass migrants. The resulting disruptive selection may ultimately lead to increased phenotypic smolt size variation provided sufficient additive genetic variance associated with smolt size. Mitigation measures at hydropower plants are thus essential for preserving sustainable populations of anadromous fish and maintaining population genetic variation.

An updated geographic distribution of Myxobolus cerebralis (Hofer, 1903) (Bivalvulida: Myxobolidae) and the first diagnosed case of whirling disease in wild-caught trout in the south-eastern United States.

Myxobolus cerebralis (Bivalvulida: Myxobolidae), the aetiological agent of salmonid whirling disease, was detected in 2 river basins of North Carolina during 2015, which initiated the largest spatial-temporal monitoring project for the disease ever conducted within the south-eastern United States (focused mainly in eastern Tennessee and western North Carolina). A total of 2072 rainbow trout Oncorhynchus mykiss, 1,004 brown trout Salmo trutta and 468 brook trout Salvelinus fontinalis were screened from 113 localities within 7 river basins during June 2017 through October 2019. Infections were detected by pepsin-trypsin digest, microscopy and the species-specific nested polymerase chain reaction (PCR) in 19 localities across 6 river basins. Myxospore morphology was indistinguishable from the published literature. In 2019, five rainbow trout that symptomatic for whirling disease (sloping neurocranium and lordosis) were captured and processed for histopathology. Myxospores were detected in the calvarial cartilage of two deformed trout with associated erosion of the cartilage consistent with reported whirling disease lesions. This is the first report of M.cerebralis in Tennessee and the first histologically confirmed cases of whirling disease in southern Appalachian (south-eastern United States) rivers and streams and expands the distribution of M.cerebralis throughout western North Carolina and eastern Tennessee.

Risk screening of the potential invasiveness of non-native freshwater fishes in the River Ob basin (West Siberian Plain, Russia)

To inform regional managers of potentially invasive non-native (NN) freshwater fishes in the principal hydrosystem that drains the West Siberian Plain, the River Ob basin, 31 extant and potential future NN fish species were screened using the Aquatic Species Invasiveness Screening Kit (AS-ISK) with respect to current and projected future climate conditions. Calibration of the AS-ISK scores, using receiver operating characteristic curve analysis, identified ‘basic risk assessment’ and ‘climate change assessment’ threshold scores of 27.5 and 34.75, respectively, with which to distinguish species that pose a high risk of being invasive in the Ob basin and those that pose a low-to-medium risk. Of the species screened, 12 ranked as high risk (black bullhead Ameiurus melas, brown bullhead Ameiurus nebulosus, grass carp Ctenopharyngodon idella, common carp Cyprinus carpio, eastern mosquitofish Gambusia holbrooki, silver carp Hypophthalmichthys molitrix, oriental weatherfish Misgurnus anguillicaudatus, rainbow trout Oncorhynchus mykiss, Chinese (Amur) sleeper Perccottus glenii, topmouth gudgeon Pseudorasbora parva, brown trout Salmo trutta, pikeperch Sander lucioperca and rudd Scardinius erythrophthalmus). The remaining species ranked as medium or low risk. Although the risk scores increased in 68% of species under climate change conditions, this affected the risk rankings of only two species: Salmo trutta decreased in rank from high to medium and Sander lucioperca increased in rank from medium to high. The outcomes of the present study, which identified 12 species for which full risk assessments are recommended, serves to inform the development of NN species policy and management in Russia.

Vertebral deformities in interspecific diploid and triploid salmonid hybrids.

Vertebral deformities in salmonid interspecific hybrids, some of which were triploidised, were assessed across three separate year classes during the freshwater life stage. Initially, eggs from a farmed Atlantic salmon Salmo salar were crossed with the sperm from a S. salar, arctic char Salvelinus alpinus or brown trout Salmo trutta. For S. salar × S. trutta, half the eggs were triploidised. In a second- and third-year class, the eggs from a farmed S. salar were crossed with the sperm from either a S. salar or a S. trutta, and half of each group was triploidised. In the two initial-year classes, all hybrids were larger than the S. salar controls, and triploid S. salar × S. trutta were larger than diploid counterparts. In the third-year class, the S. salar × S. trutta were smaller than the S. salar, in contrast to the initial 2 year classes, although the triploid hybrids were still larger than the diploids. In the third-year class, a high degree of spontaneous triploidy was also observed in the putative diploid groups (between 16 and 39%). Vertebral deformities were consistently higher in pressure-shocked triploids than diploids, irrespective of hybridisation, but there was no consistent effect of hybridisation among experiments. Although this study was not able to explain the contrasting results for vertebral deformities between year classes, triploid S. salar × S. trutta can demonstrate impressive freshwater growth that could be of interest for future farming programmes.

Could mycotoxigenic Fusarium sp. play a role in ulcerative dermal necrosis (UDN) of brown trout (Salmo trutta morpha trutta)?

Fusarium infections have been reported in aquatic animals, but are still poorly investigated in wild salmonids. The aim of the study was to determine the impact of the fungi and their toxins on the health status of brown trout (Salmo trutta morpha trutta) migrating from the Baltic Sea to the freshwater. Individuals from the wild brown trout population exhibiting ulcerative skin lesions were collected from the Słupia River in Poland and subjected to microbiological, histopathological, and hematological examinations, as well as toxicological analysis for a presence of mycotoxins. The results of microflora isolation from the brown trout skin samples revealed the presence of conditionally pathogenic bacteria and fungi classified by molecular techniques as Fusarium spp. Toxicological analysis allowed for detection of zearalenone (ZEN) in the liver, kidney, and gastrointestinal tract of the fish. In several cases, there was α-zearalenone (α-ZEL) identified at trace levels in the liver, as well as sterigmatocystin and enniatin B at low levels in the kidney and the liver. Histopathological examination revealed the presence of fungal hyphae disrupting the epidermis and penetrating into the necrotic dermis and hypodermis. The decreased values of the blood parameters, i.e., hemoglobin concentration (HGB), packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and white blood cell count (WBC), were indicative of osmoregulation failure being a consequence of the skin damage. The results of the study provide new information regarding Fusarium sp. infection in brown trout and serve as the basis for further research on the potential impact of the fungi and their mycotoxins on the Baltic salmonid population, including their role in ulcerative dermal necrosis.

Dome-shaped selectivity in LB-SPR: Length-Based assessment of data-limited inland fish stocks sampled with gillnets

Inland fisheries can support complex social-ecological systems and contribute to food security. However, many target stocks lack monitoring and quantitative assessment. There may be scope to apply current data-limited assessment models in these fisheries. The Length-Based Spawning Potential Ratio (LB-SPR) model requires only fish length data and input estimates of key life history parameters. LB-SPR has been seldom applied in inland systems, partly due to the current model assumption of asymptotic fishing gear selection, characteristic of trawls. In contrast, most inland fisheries operate gillnets or hooks, having dome-shaped selection curves. This is problematic because the largest size classes of fish are not fully retained by the gear, but their absence in the catch will be assumed by the LB-SPR model to reflect fishing mortality. LB-SPR was extended to include dome-shaped selection. Case study assessments were undertaken using survey gillnet catches of brown trout Salmo trutta from four Irish lakes. Bayesian Monte Carlo methods were used to quantify uncertainty around estimates of life history parameters for each stock. Despite small sample sizes, the model produced estimates of SPR that corresponded to expert knowledge of stock status. The extended LB-SPR can be applied to assess data-limited inland fish stocks, and other stocks for which selection is dome-shaped.

Ecological and Biochemical Status of the Atlantic Salmon Salmo salar L. and the Brown Trout Salmo trutta L. at Early Stages of Development

A review of original and published data on the biochemical status of two salmonid species, the Atlantic salmon Salmo salar L. and the brown trout Salmo trutta L., encompasses the results on fish embryogenesis and the early development of fry of different ages during the freshwater period of life at different stages of life history (fingerling, parr, smolt) with inhabitation of the riverine biotopes of the northwest Russia, which differ in ecological and hydrological conditions. Data on the total lipid content, reserve lipids (triglycerides and cholesterol ester) and structural lipids (phospholipids and their fractions, cholesterol), fatty acids, activity of enzymes of carbohydrate metabolism, energy metabolism, and intracellular proteolysis are considered, along with some molecular-genetic indices of muscular tissue growth (the expression level of genes controlling myogenesis, as well as myostatin and heavy chain of myosin). Biochemical differences are already found in the embryos of the studied salmon fish; they determine the specifics of the interaction of larvae and fry with the habitat. As a result, when leaving the redds, some hatchlings may have certain metabolic advantages that facilitate their settling on better nursery grounds. Among all of the studied age groups, the “youngest” groups (0+, 1+) stand out, both in regard to the level of biochemical metabolism and the degree of difference between phenotypic groups inhabiting microbiotopes with different ecological, trophic, and hydrological conditions.

Food Differentiation of Juvenile Brown Trout Salmo trutta L. as a Mechanism for Expanding the Food Supply of the Population

The feeding habits of brown trout (age 2+ and 3+ years) in the small Orzega River (Lake Onega basin) are analyzed with an autumn decrease in the number of accessible food items. Along with the previously determined mechanisms for compensating for this phenomenon (feeding directly from the bottom and consumption of large items), a sharp increase in the variability of the individual feeding habits of sea trout in October is revealed both by the composition of the contents of its stomachs and by the amount of consumed feed. The food differentiation of individuals makes it possible to expand the food supply of the brown trout population in the river and effectively use the food resources of the small watercourse, which is particularly important during the period of low availability.

Acanthocephalan parasites collected from Austrian fishes: molecular barcoding and pathological observations.

Acanthocephalan parasites were collected from the intestinal tracts of 137 predominantly wild fish (1 barbel Barbus barbus, 3 European chub Squalius cephalus, 13 rainbow trout Oncorhynchus mykiss and 120 brown trout Salmo trutta) from 12 localities. The condition factor, intensity of acanthocephalan infection and pathological lesions, if applicable, were documented. Routine bacteriology and virology were performed, and the brown trout were additionally tested for the presence of the myxozoan parasite Tetracapsolioides bryosalmonae by PCR. In total, 113 acanthocephalans were barcoded by sequencing a section of the mitochondrial cytochrome oxidase subunit I (COI) gene. Barcoding of the acanthocephalan tissues resulted in 77 sequences, of which 56 were assigned to Echinorhynchus truttae (3 genotypes), 11 to Pomphorhynchus tereticollis (9 genotypes), 9 to Acanthocephalus sp. (5 genotypes) and 1 to Neoechinorhynchida. Most of these genotypes were detected for the first time. Statistically, the acanthocephalan infection did not have an impact on the condition factor of the brown trout. Infection with P. tereticollis caused more severe pathological changes in the digestive tract than E. truttae. The present study provides new data regarding the distribution of acanthocephalan species in Austria and their impact on individual fish. In addition, new barcoding data from acanthocephalan parasites are presented, and the occurrence of P. tereticollis in European chub in Austria and in brown and rainbow trout in general was confirmed for the first time.

Exposure to carbamate fungicide iodocarb does not affect reproductive behavior or milt volumes in precocious male brown trout (Salmo trutta L.) parr

Previous studies with olfactory-disturbing pesticides resulted after exposure in disturbed behavior and physiology in fish. In the present experiment, reproductive behavior and milt volumes of precocious brown trout (Salmo trutta L.) male parr were studied in a large stream aquarium after exposure to the olfactory-disturbing fungicide 15 μg l−1 IPBC (iodocarb; 3-iodo-2-propynyl butyl carbamate) for 96 h. The statistical analyses did not reveal any significant differences for time attending females between controls and IPBC-exposed males. Furthermore, there were no significant differences in milt volumes. However, when taking all fish into consideration, there were significant differences in milt volumes between parr that had been attending females and those had not been attending females. Controls that had attended females had significantly higher milt volumes than controls or IPBC-exposed males that had not attended females. Taking all control and IPBC parr into consideration, there was a statistically significant positive correlation between time attended females and volume of milt and gonadosomatic index (GSI), respectively. In summary, 15 μg l−1 IPBC did not have any significant effects on mature male parr reproductive behavior and milt volumes.

The effects of fisheries management on harvest rates of native and non‐native salmonid fish species

In central Europe, both brown trout Salmo trutta and European grayling Thymallus thymallus are threatened native salmonid species with high value in recreational angling and nature conservation. On the other hand, rainbow trout Oncorhynchus mykiss and brook trout Salvelinus fontinalis are intensively stocked non-native species of high angling value but no value for nature conservation. This study tested if harvest rates of native salmonids are negatively correlated to intensive stocking and harvest rates of non-native salmonids in inland freshwater recreational fisheries. Data were collected from 250 fishing sites (river and stream stretches) over 13 years using mandatory angling logbooks. Logbooks were collected from individual anglers by the Czech Fishing Union in the regions of Prague and Central Bohemia, Czechia (central Europe) and processed by the author of this study. In result, anglers harvested 200,000 salmonids with total weight of 80 tons over 13 years. Intensive stocking of multiple salmonid species lead to slightly lower harvests of native salmonids. Inversely, intensive harvests of multiple salmonid species lead to slightly higher harvest of native salmonids. Recapture rates of stocked salmonids were relatively low (0.6%–3.7%), proving fish stocking moderately ineffective. Since the effects of non-native salmonid stocking and harvest rates on native salmonid harvest were significant but not strong, it is suggested that rivers and streams that support fishing for non-native salmonids still support fishing for native salmonids. However, this idea does not apply for fishing sites with really high intensity of non-native salmonid stocking – harvest rates of natives were very low on these fishing sites.

The viability of the crustacean Eurycercus lamellatus (Branchiopoda, Cladocera) in a high mountain area in southern Norway

The branchiopod Eurycercus lamellatus is widely distributed in Norwegian lakes, ranging from coastal to alpine areas. On the Hardangervidda mountain plateau in southern Norway, E. lamellatus was searched for in 144 lakes in 11 catchments in the western and 16 catchments in the central and eastern areas. Their occurrence is mainly based on the diet of brown trout Salmo trutta. Eurycercus lamellatus was recorded in 25% and 70% of the lakes in these two areas, respectively. This may be due to striking differences in the environmental conditions, with more dilute water and lower water temperatures in western areas, and hence shorter growing seasons. The occurrence of E. lamellatus in central and eastern catchments increased with lake size, being found in 65% and 85% of lakes with a surface area of <2.0 and ≥2.0 km2, respectively. In the western area, E. lamellatus occurred less frequently in lakes above 1000 m a.s.l. That was not the case for lakes in central and eastern catchments. In this central part of Hardangervidda, the relative abundance of E. lamellatus in the diet of brown trout was obtained from five different lakes, showing that they were preyed upon throughout the growing season (June to October). When the two big crustaceans Gammarus lacustris and Lepidurus arcticus are at low densities in these lakes, E. lamellatus became the staple food item for brown trout, except for larger fish (>400 mm). However, under high predation pressure, E. lamellatus also contributed significantly to the diet of larger fish. The abundance of E. lamellatus seems to vary highly on a yearly basis in one of the lakes (Sandvatn). Even though E. lamellatus is described as a typical littoral species, it was common down to depths of 15 m.

Invasive freshwater fish (Leuciscus leuciscus) acts as a sink for a parasite of native brown trout Salmo trutta

Invasive species tend to acquire native parasites from their invaded range over time. In these cases, native host-parasite dynamics may be altered as a result of differences in parasite population biology and host competency between invasive and native hosts. Competent invasive hosts are likely to increase transmission to native hosts while incompetent invasive hosts may dilute infection in natives. In this study, we used a freshwater fish system and a survey approach to compare the host competency and population biology of a dominant helminth parasite, Pomphorhynchus tereticollis, between native brown trout (Salmo trutta) hosts and invasive dace (Leuciscus leuciscus) hosts over 2 years at the core and edge of dace’s invasive range in Ireland. Our results show that, although dace acquired P. tereticollis, dace had prevalent and high intensity infections of immature extra-intestinal worms while prevalence of adult worms was consistently higher in brown trout. The majority of parasite individuals infecting dace were immature extra-intestinal forms and, in contrast to brown trout, parasites in dace did not attain sexual maturity. In addition, brown trout from the invasion core where dace have been established the longest had a lower abundance of P. tereticollis, indicating that by taking up but not transmitting infective stages of the parasite, invasive dace may dilute P. tereticollis infection in the native host.

The freshwater shrimp Gammarus lacustris (Malacostraca, Amphipoda) in lakes on the Hardangervidda mountain plateau, southern Norway: distribution and environmental requirements

The distribution of the amphipod Gammarus lacustris on the Hardangervidda mountain plateau was mapped by screening published data from 245 lakes in 11 and 16 catchments in western and central/eastern areas, respectively. These data are primarily based on stomach analyses of brown trout Salmo trutta. In central/eastern areas, G. lacustris was recorded in 79% of all the lakes examined, while there are only two former records (4%) in the western area. The distribution pattern of G. lacustris on Hardangervidda appears to be related to environmental conditions. The apparent absence of G. lacustris in the western area may be explained by a combined effect of cold water due to higher deposits of snow and water with low ionic strength as a consequence of its bedrock of Precambrian gneisses and granites with little or no moraine cover. However, lakes in central/eastern areas sustain G. lacustris in spite of dilute water, as G. lacustris has been recorded in 89 lakes of which 28% had calcium concentration <1.0 mg L-1, eight of them with pH <6.0. The lower lethal threshold for calcium concentration seems to be ~0.5 mg L-1. Gammarus lacustris was found in lakes at altitudes of 832 to 1396 m a.s.l. Furthermore, their occurrence increased significantly with lake size, being 69% in lakes <1.0 km2 and 97% in larger lakes. The number of refugia with better water quality is likely to increase with lake size. Gammarus lacustris is highly searched for as prey by all size groups of brown trout (15-45 cm). Access to proximity refugia that reduce predation pressure from fish may also increase with lake size. Climate changes are now in progress in this mountain area, and detailed mapping of G. lacustris is important in order to trace future range changes.

Stairs pipe culverts: flow simulations and implications for the passage of European and Neotropical fishes

Culvert fishways can improve upstream fish passage in brooks and have been studied in relation to North American and Australian species. Research focusing on fish species from other world regions and, in parallel, effect of baffles on flow turbulence is rare. In this paper we present computational fluid dynamics of a sloped baffle culvert, called “stairs pipe”. We aimed at evaluating if: (1) the flow met the requirements of Neotropical and European species; (2) the flow turbulence was acceptable for fish passage; (3) the flow limited fish movements. The average flow velocities for 5% slope and discharge rates of 5–13 L/s were lower than the prolonged speeds of three Neotropical species, namely, piau (Leporinus reinhardti), mandi (Pimelodus maculatus), and lambari (Piabarchus stramineus) and higher than the sustainable speeds of three European species, namely, dace (Leuciscus leuciscus), barbel (Barbus barbus), and brown trout (Salmo trutta). The turbulence flow characteristics i.e. levels of turbulence kinetic energy were similar to those produced by comparable culverts but higher than those in a fish ladder. The water jet created by baffles at an angle of 30° can limit fish movements, restraining them from jumping. The stairs pipe might improve upstream fish movement in different regions of world; nevertheless, further experimental research should concern the use of different swimming modes in the culvert flow.