Fish early life stage tests as a tool to assess embryotoxic potentials in small streams

Early life stage (ELS) studies with brown trout(Salmo trutta f. fario L.) andstone loach (Barbatula barbatula L.)were performed between 1995 and 2000 toevaluate embryotoxic potentials in twodifferently polluted streams in southwestGermany. With both species, semistatic exposureexperiments with water samples and sedimenteluates were conducted in the laboratory.Additionally, brown trout ELS tests wereperformed in flow-through systems in thesemi-field and in the field. Thus, differentlevels of complexity of environmentalconditions were addressed which allowed thestudy of effects of xenobiotic contamination,temperature, and sediments on the success ofembryonic development. Additionally, effects ofwater from the polluted stream on fertilizationof brown trout eggs were determined. In themore polluted stream, xenobiotics caused anembryotoxic potential for both brown trout andstone loach, and viability of exposed browntrout eggs was drastically reduced by suspendedsolids in the water which covered the eggs.Additionally, fertilization rates of browntrout eggs were significantly decreased inwater of the more polluted stream. In the lesspolluted stream, low water temperature andinfestations by protozoic ectoparasites causedmortality of embryos. In this stream, pollutionand sediment effects were not observed. Resultsmade evident that in the more polluted streamrecruitment of brown trout was drasticallyimpaired.     

Ultrastructural biomarkers as tools to characterize the health status of fish in contaminated streams

Ultrastructural biomarkers in gill, liver, andkidney of brown trout (Salmo truttaf. fario) and stone loach (Barbatulabarbatula) were investigated over afive year period. The cellular damage of theorgans was assessed semi-quantitatively basedon a three-step classification ofultrastructural responses. Data obtained forfish exposed under semi-field conditions in twodifferently polluted test streams and in thelaboratory demonstrated that the ultrastructureof the organs can be correlated with differentpollutant exposure conditions. Cellular damagewas generally more severe in fish exposed to acomplexly polluted stream than in those exposedto a moderately polluted stream or to tap waterin the laboratory. Histopathological effects inliver and gill of trout were more pronounced inferal fish than in transplanted fish, whereasresponses in the kidney in both species, and inliver and gill of loach, were similar forintroduced and feral fish. In a laboratoryexperiment where trout were exposed todifferent mixtures of pollutants includingpesticides, PAH, and ammonia, only theultrastructure of kidney and liver showedsignificant differences between the threeexperimental set-ups. In a recovery experiment,where trout were transferred from thesemi-field condition back to the laboratory,ultrastructural investigations showed adifferential capacity of the respective organsto recover from stress under field conditions.Kidney and liver fully recovered after threemonths under control condition whereas gillsdemonstrated only partial recovery.     

Hepatic biotransformation enzymes of fish exposed to non-point source pollution in small streams

The response of hepatic phase I and phase IIbiotransformation enzymes in brown trout(Salmo trutta f. fario) and stone loach(Barbatula barbatula) to differentpollution exposure scenarios was investigatedduring a 5-year-study. Phase I enzymes wereassessed by means of7-ethoxyresorufin-O-deethylase (EROD) activityand cytochrome P4501A (CYP1A) protein level,and phase II enzymes were measured by thecatalytic activity of glutathione-S-transferase(GST). Fish were exposed in the laboratory totap water (controls) or under semi-fieldconditions in so-called bypass systems to waterfrom two streams, with one of the streams(Krähenbach) receiving contaminants mainlyfrom non-point sources (for instance, surfacerun-off), and the second stream (Körsch)receiving contaminants from both non-pointsources and point sources (sewage plants). Inaddition to the fish in the bypass systems,feral fish from the streams were sampled. Thequestions addressed by the study were: (1) isit possible to discriminate the study sites onthe basis of hepatic biotransformation indices?(2) are the metabolic enzyme responses of thetwo species, brown trout and stone loach,comparable? (3) are the metabolic enzymeresponses of fish from the bypass systemscomparable to those of feral fishes? HepaticEROD activities were elevated in both browntrout and stone loach exposed in the bypasssystems compared to the laboratory control. Adiscrimination of the two field sites relativeto pollution intensity was possible by hepaticEROD activities of brown trout only, whereasbiotransformation enzymes of stone loach showedno consistent differences between the stream.Hepatic GST levels of both speciesdid not discriminate between the streams orbetween streams and laboratory. The enzymeresponses measured in fishes from the bypasssystems were comparable to those of feralfishes living in the streams. The findings ofthis study point to critical factors for thebiological monitoring of low-level pollutionwith complex chemical mixtures, including theselection of appropriate test species,monitoring endpoints, and sampling strategies.     

Histopathological alterations and parasite infection in fish: indicators of multiple stress factors

Within the scope of the multidisciplinaryresearch project Valimar (1995–1999), thepresent study emphasizes the use ofhistopathological investigations to evaluatethe effects of the different chemical impactof two small streams on the general health andcondition of the two sentinel fish species,brown trout (Salmo trutta f.fario) and loach (Barbatula barbatula).Parasitological investigations were alsoincluded to assess a possible relationshipbetween toxicant exposure, parasitic load, andthe occurence of histopathological organchanges. According to the multitiered approachof the Valimar project, fish from the field,individuals exposed to stream water undersemi-field conditions, and fish fromlaboratory experiments were investigated.Under semi-field conditions, thehistopathological responses in brown troutproved to reflect the different levels ofcontamination of the two small streams moreclearly than those detected in loach. Whencaptured from the field, both fish speciesrevealed, in most cases, a higher degree ofhistopathological alterations than thoseindividuals exposed at the respective siteunder semi-field conditions. Simulation of thetoxic load of the more polluted stream in alaboratory experiment did not result in thesame kind of tissue lesions in brown trout asin the field and semi-field investigations.Whereas results from the laboratoryexperiments could be specified astoxicant-induced, the histopathologicalalterations in fish from both semi-field andfield studies represent stress responses whichintegrate the effects of various abiotic andbiotic stress factors including both toxicantsand parasitic diseases.     

Establishing Causality between Pollution and Effects at Different Levels of Biological Organization: The VALIMAR Project

The study summarizes the objectives of the VALIMAR project and gives selected examples of biomarker responses that allow causal relationships to be established between exposure and biological effects at different levels of biological organization. In this project, active and passive biomonitoring experiments with brown trout (Salmo trutta f. fario) and stone loach (Barbatula barbatula) were performed in two small streams in southern Germany between 1995 and 1999 in parallel with investigations on contaminant mixtures in the laboratory in order to evaluate the suitability of biomarkers representing different levels of biological organization for the assessment of pollution in small streams. In addition to biomarker studies, the morphology of the test streams was characterized and limnological and chemical parameters were monitored. Early life stage tests and ecological studies of brown trout and stone loach population demography, of the fish assemblages, and the macro- and meiozoobenthos communities in the two test streams were included in the project. Several causality criteria were addressed by means of combined (1) laboratory and field studies, (2) chemical, biological, and statistical investigations, and (3) in vivo and in vitro studies that allowed establishment of cause-effect relationships at different biological levels. The comparison of results obtained at these levels allowed identification of mechanisms responsible for the respective effects (coherence of association, biological plausibility). Finally, individual responses (biomarkers, bioindicators) could be extrapolated to higher biological levels (population, community) thus addressing the criteria of ‘time order’ and ‘coherence of association’.     

Trophic relationships of two species of grebe on a prairie lake based on stable isotope analysis

Loch Leven, U.K., contains brown trout (Salmo trutta), eel (Anguilla anguilla), minnow (Phoxinus phoxinus), perch (Perca fluviatilis), pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus), with brook lamprey (Lampetra planeri) and stone loach (Barbatula barbatula) also present in its tributaries. Arctic charr (Salvelinus alpinus), Atlantic salmon (Salmo salar) and flounder (Platichthys flesus) are now extinct. The brown trout population has supported a world-renowned recreational fishery for over a century, although a decline in fishery performance led to extensive stocking between 1983 and 2006, including with non-native rainbow trout (Oncorhynchus mykiss). This review combines historical information with contemporary gill-net and hydroacoustic surveys. In 2008, brown trout, perch and three-spined sticklebacks were abundant, but pike and stone loach were rare. The obstruction of migratory routes was probably responsible for the loss of Atlantic salmon and flounder, while a lowering of water level likely caused the extinction of Arctic charr and contributed to a reduction in pike abundance. Perch abundance has fluctuated markedly, being influenced by disease and eutrophication, although a reduction in nutrients and associated recovery of macrophytes are likely to have benefitted this species. Although the brown trout population has undoubtedly shown a long-term decline, individuals are currently in excellent condition.     

Diversity of rotifers from northeastern U.S.A. bogs with new species records for North America and New England

In order to assess the effects of pollution on recruitment of brown trout (Salmo trutta f. fario L.) exposure experiments with brown trout early life stages were performed in two differently contaminated small streams near Stuttgart, southwest Germany, and in a control situation in the laboratory. Pollution in the more polluted stream is mainly due to effluents of municipal sewage treatment plants and to the influx of surface waters from areas of intense agriculture activity. Additionally, the water carries high particle loads, especially after rainfall events. Water quality of the less polluted stream is occasionally influenced by agriculture activity in the vicinity. For the exposure of trout early life stages incubators were used, which allowed frequent examinations without serious disturbance of the exposed organisms and thus the development could be monitored over time. Compared to the less polluted stream and the control, in the more polluted stream high mortality rates, the lowest hatching success, and lowest values for growth occurred. In the less polluted stream, mortality rates were comparably low in prehatching stages, but high in hatchlings and juveniles due to heavy infestations with protozoic ectoparasites Chilodonella cyprini (Moroff, 1902) and Ichthyobodo necator (Henneguy, 1883). However, pollution-related effects were not detected in this stream. Differences in developmental rates between the different treatments were correlated with different water temperatures in the two streams and the control. For the more polluted stream, previous studies have indicated embryotoxic potentials mediated by pollutants. The present study indicates that in this steam, additionally, fine solids which infiltrate stream gravels may seriously affect development of brown trout early life stages.     

The hepatic stress protein (hsp70) response to interacting abiotic parameters in fish exposed to various levels of pollution

Two indigenous fish species, brown trout (Salmo trutta f. fario) and stone loach(Barbatula barbatula) were exposed tocomplex stressors (mixtures of environmentalpollutants) in laboratory and semi-fieldexperiments (aquaria connected to stream water)and in field studies. As a biomarker of effect,the level of the 70 kD heat shock protein(hsp70) was quantified in the liver of troutand loach. Laboratory experiments withdifferent pollutant mixtures did not mimic thehsp70-inducing or inhibiting potential of fieldconditions, whereas effects of long-termexposure in the bypass systems showed asignificant correlation with effects recordedin feral fish. Laboratory as well as semi-fieldstudies revealed the stress response to followan optimum curve, resulting in a maximum hsp70level under stress but rather low hsp70 levelswhen stressors (chemicals, high temperature)become too severe. Consequently, the hsp70level in the liver of both species was highlyseason-dependent with two peaks in late springand fall, and rather low hsp70 levels insummer, particularly in fish exposed to waterand sediment of the complexly polluted stream.In winter, the low hsp70 level of lab controlswas elevated by exposure to natural streamwater only, but elevation did not occur undercontrol conditions independent of apre-exposure to polluted streamwater two months earlier. Despite the highvariability of the hsp70 level within one yearand among five subsequent years, patternanalysis indicated the prevailing importance ofwater temperature on stress protein response.Temperature alone, however, could not explainthe regularly observed low summer levels inhsp70. Non-linear regression analysis on labcontrols revealed an optimum temperature(T_opt) for the highest hsp70 level forboth fish species. In both investigated streams, thechemical influence led to a decrease in thehsp70 level only when T_opt was surpassedby the ambient temperature at the same time.Otherwise, the chemical impact resulted in anelevated hsp70 level relative to the control.The study demonstrated the suitability of hsp70stress protein levels to integrate the responsedynamics of several different stressors and,therefore, to effectively function as abiomarker for the integrated effect of allenvironmental stressors acting on an organism(not only of chemical pollution). Rathercomplex kinetics of hsp70 elevation anddecrease should be taken into consideration.     

Habitat-Specific Nitrogen Dynamics in New Zealand Streams Containing Native or Invasive Fish

Streams are important sites of nutrient transport and transformation in the landscape but little is known about the way in which individual taxa or individual habitats (riffles and pools) influence nutrient dynamics within stream reaches. We used 5-week additions of a stable isotope (¹⁵NH₄Cl) tracer to investigate nitrogen dynamics in pools and riffles of two New Zealand streams, one with native fish (Galaxias depressiceps) and the other with invasive brown trout (Salmo trutta). In New Zealand, brown trout initiate a trophic cascade leading to increased algal biomass that we predicted would lead to higher N uptake and retention. Uptake of NO₃, but not ammonium, was greater in the trout stream. Rather than causing a large increase in N demand, trout may induce a reallocation of N uptake and retention among food web compartments in different habitats. The largest differences between streams were apparent in riffles, where most uptake and retention of N occurred. In the trout stream, uptake rate by epilithon in riffles was more than six times greater than uptake rates of any other compartment. In the Galaxias stream, several compartments in both habitats had similar uptake rates. Epilithon also accounted for a larger percentage of the ¹⁵N retained in the study reach in the trout stream (51%) than the Galaxias stream (34%). Our results show that an individual predatory taxon (in our case an invader) can influence N dynamics in streams but that the magnitude and location of the impact depend on a range of abiotic and biotic factors involved in N dynamics in streams.     

Phylogenetic origin of <Emphasis Type="Italic">Salmo trutta</Emphasis> L 1758 from Sicily,based on mitochondrial and nuclear DNA analyses

The phylogenetic status of brown trout Salmo trutta L 1758 in Sicily is uncertain as some reports describe these trout as S. macrostigma or S. cettii on one hand while other, contradictory reports imply a hatchery origin on the other. In order to clarify this situation, we performed sequence analysis of the mtDNA control region and restriction fragment analysis of the nuclear lactate dehydrogenase (LDH-C1*) gene. A single mitochondrial haplotype (At-s6) found previously in brown trout in Morocco, and two alleles at LDH-C1* (the ancestral*100, at a high frequency, and *90) were revealed. Our results suggest that Sicilian brown trout are native and that they probably colonized Sicily from west to east in an expansion, from the Atlantic Ocean basin, along the North-West African coast. Handling editor: C. Sturmbauer     

Response of stream fish to improved water quality: a comparison between the 1960s and 1990s

1. The effect of improved water quality on fish assemblages in streams in southern Sweden was assessed by comparing species composition at 161 sites and water quality at twenty-nine sites in the 1960s and the 1990s. 2. Water quality had improved and there was an increase in the number of sites or catchments with brown trout (Salmo trutta), stone loach (Barbatula barbatula) and eel (Anguilla anguilla). The response was greatest for brown trout and was best explained by increased oxygen concentrations. 3. The number of sites with nine-spined stickleback (Pungitius pungitius), ide (Leuciscus idus) and brook lamprey (Lampetra planeri) decreased between the 1960s and 1990s. The decrease was greatest for nine-spined stickleback and was related to the increase in sites with trout, suggesting that nine-spined stickleback may be sensitive to predation or competition. 4. Improved water quality has led to recolonization by brown trout, probably enabling biotic interactions to play a larger role in structuring fish assemblages. Improving water quality was an effective method for rehabilitating fish populations in streams where natural colonization was possible.     

Ultrastructural changes in fish gills as biomarker to assess small stream pollution

In order to verify the principal suitability of gill ultrastructure as a biomarker, semi-field studies with two endigoneous fish, trout (Salmo trutta f. fario) and loach (Barbatula barbatula), were performed. The fish were exposed in flow-through systems to one heavily polluted (K?rsch) and one lightly polluted small stream (Kr?henbach) in South-West Germany. Ultrastructural responses in gills were correlated with limnological and chemical data recorded over a 2 year period in each stream. After 8 weeks of exposure to the heavily polluted stream, fish showed ultrastructural changes in the gills, such as cell proliferation, dilation of the endoplasmic reticulum, hyperplasia, hypersecretion, and epithelial lifting in chloride, epithelial, and mucus cells. The results of the study demonstrate that ultrastructural reactions in the gills of fish kept under semi-field conditions are potentially useful biomarkers indicating small stream pollution.     

Heterochromatins and band karyotypes in three species of salmonids

Summary The heterochromatins of rainbow trout (Salmo gairdneri R.), brown trout (Salmo trutta fario L.) and brook trout (Salvelinus fontinalis M.) were characterized by sequential chromomycin A₃/distamycin A/DAPI (CDD) and DAPI/actinomycin D (DAPI/AmD) fluorescence. On most biarmed chromosomes, an equilocal localization of prominent DAPI/AmD positive, chromomycin A₃ negative, AT-rich blocks at the centromeres were observed in all three species. Band karyotypes of the three species were established. In rainbow trout, several DAPI/AmD positive heterochromatin blocks behaved positive in a silver-staining method. Mitotic and interphase studies proved the presence of inter-individual NOR variation in brown trout. The NORs of brook trout were localized on chromosomes 5, 10, 14, 15 and 29.     

Winter sheltering by juvenile brown trout (Salmo trutta) – effects of stream wood and an instream ectothermic predator

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Effects of biotic and abiotic factors on the distribution of trout and salmon along a longitudinal stream gradient

Synopsis We examined the influence of biotic and abiotic factors on the distribution, abundance, and condition of salmonid fishes along a stream gradient. We observed a longitudinal change in fish distribution with native cutthroat trout, Oncorhynchus clarki utah, and introduced brown trout, Salmo trutta, demonstrating a distinct pattern of allopatry. Cutthroat trout dominated high elevation reaches, while reaches at lower elevations were dominated by brown trout. A transition zone between these populations was associated with lower total trout abundance, consistent changes in temperature and discharge, and differences in dietary preference. Variation in cutthroat trout abundance was best explained by a model including the abundance of brown trout and diel temperature, whereas variation in brown trout abundance was best explained by a model including the abundance of cutthroat trout and discharge. These results suggest the potential for condition-mediated competition between the two species. The results from our study can aid biologists in prioritizing conservation activities and in developing robust management strategies for cutthroat trout.     

Use of three types of stream-margin habitat by age-0 brown trout late in the growing season

The use of stream-margin habitat by age-0 salmonids has been studied, but differences in use among various types of habitat along stream margins has not been addressed. We described the nighttime use of habitat features by age-0 brown trout (Salmo trutta) among three types of stream-margin habitat late in the growing season (August–September) and assessed the extent to which use of habitat features within each type differed over the sampling period. Differences in water depths, water velocities, distances from shore, and substrate at the locations of fish along the margins of pools, the margins of riffles, and in backwaters were studied. Variation in habitat use also was observed during the study period as fish increased in length. Our observations are important considerations when developing habitat suitability criteria for assessment of instream-flow needs of age-0 brown trout.     

Diurnal shifts in use of summer habitat by age-0 brown trout in a regulated mountain stream

Diurnal shifts in habitat use by age-0 (< 50 mm total length) brown trout (Salmo trutta) were observed from June to July 1989 and 1990 in low-gradient (< 1% channel slope) reaches of Douglas Creek, Medicine Bow National Forest, Wyoming. Fish were visually located during day and night, and water depth, water velocity, distance from the stream edge, substrate, habitat type, and cover were determined at each location. The fish were found predominantly in locations with slow water velocities in stream-margin and backwater-pool habitats. They were observed in slower water, closer to the stream edge at night than during the day.     

Invading rainbow trout usurp a terrestrial prey subsidy from native charr and reduce their growth and abundance

Movements of prey organisms across ecosystem boundaries often subsidize consumer populations in adjacent habitats. Human disturbances such as habitat degradation or non-native species invasions may alter the characteristics or fate of these prey subsidies, but few studies have measured the direct effects of this disruption on the growth and local abundance of predators in recipient habitats. Here we present evidence, obtained from a combined experimental and comparative study in northern Japan, that an invading stream fish usurped the flux of allochthonous prey to a native fish, consequently altering the diet and reducing the growth and abundance of the native species. A large-scale field experiment showed that excluding terrestrial invertebrates that fell into the stream with a mesh greenhouse reduced terrestrial prey in diets of native Dolly Varden charr (Salvelinus malma) by 46–70%, and reduced their growth by 25% over six weeks. However, when nonnative rainbow trout (Oncorhynchus mykiss) were introduced, they monopolized these prey and caused an even greater reduction of terrestrial prey in charr diets of 82–93%, and reduced charr growth by 31% over the same period. Adding both greenhouse and rainbow trout treatments together produced similar results to adding either alone. Results from a comparative field study of six other stream sites in the region corroborated the experimental findings, showing that at invaded sites rainbow trout usurped the terrestrial prey subsidy, causing a more than 75% decrease in the biomass of terrestrial invertebrates in Dolly Varden diets and forcing them to shift their foraging to insects on the stream bottom. Moreover, at sites with even low densities of rainbow trout, biomass of Dolly Varden was more than 75% lower than at sites without rainbow trout. Disruption of resource fluxes between habitats may be a common, but unidentified, consequence of invasions, and an additional mechanism contributing to the loss of native species Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Summer and fall microhabitat utilization of juvenile bull trout and cutthroat trout in a wilderness stream, Idaho

Microhabitat use and availability were evaluated and compared between different size classes of juvenile resident bull trout (Salvelinus confluentus) and cutthroat trout (Oncorhynchus clarki) in a small wilderness stream within the South Fork Clearwater River basin, Idaho. The objective was to determine if utilization of measured habitat characteristics changed from summer to late fall. Sampling of fish was conducted with night snorkeling. During the summer, smaller juvenile bull trout (<66 mm) total length (TL) were associated with shallow stream margins over coarse substrates. In the fall, they moved to significantly deeper, lower velocity water, and closer to cover (p<0.05), but maintained their association with coarse substrates. During the summer, larger juvenile bull trout and larger juvenile cutthroat trout (66–130 mm TL) occupied significantly deeper water than smaller juvenile bull trout (p<0.05). Generally, larger juvenile bull trout were found closer to the bottom and in lower velocity water than larger juvenile cutthroat trout (p<0.05). In the fall, larger juvenile bull trout and larger juvenile cutthroat trout were associated with significantly deeper, lower velocity water located closer to cover than in summer (p<0.05). However, cutthroat trout occupied slightly deeper water over finer substrates than bull trout. Deep water with low velocities evidently provide important rearing areas for large bull trout and large cutthroat trout in the fall. Land management practices that maintain such environments will benefit these species.