Chemometric discrimination between streams based on chemical, limnological and biological data taken from freshwater fishes and their interrelationships

The VALIMAR project aims at identifyingbiomarkers in fish that are suitable to detectand predict environmental stress from chemicalpollution or from limnological parameters inthe field. For two small streams in SouthernGermany, concentration values of 31contaminants in water and sediment and 12 limnological parameters as well as 27 biomarkersmeasured in brown trout and stone loach werecollected. All these physicochemical andbiological parameters have been analysed forpatterns that discriminate between the streams,using discriminant analysis (DA), analysis ofvariance (ANOVA) and of covariance (ANCOVA), and principal component analysis (PCA) asmultivariate statistical techniques. Moreover,the biological data were analyzed with respectto species-specific patterns, and the partialleast-squares regression method (PLS) was usedto study the impact of chemical and limnological data on the health status of the targetspecies as characterized by the biomarker data.Abiotic as well as biotic data yielded goodseparations between the streams, with theultrastructure of gill (US-gill) being thestrongest discriminator variable among all 27biomarkers tested. With regard to the two fishspecies, the biomarker data from brown troutshow significantly greater differences betweenthe two streams than the biological responsesin stone loach. Application of PLS yieldssignificant regression models for only fewbiomarkers including US-Gill, which can bepartly traced back to significant noise levelsin the data set as quantified by permutationtests.     

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.     

Alterations of selected metabolic enzymes in fish following long-term exposure to contaminated streams

In order to assess the suitability ofalterations in activities of selected metabolicenzymes as biomarkers of chemicalcontamination, juvenile brown trout (Salmotrutta f. fario) and adult loach (Barbatula barbatula) were exposed to nativesurface waters from Krähenbach andKörsch, two differently polluted smallstreams in Southern Germany. As biomarkers ofexposure, a set of metabolic enzymes comprisinghexokinase, phosphofructokinase,glucose-6-P-dehydrogenase, malic enzyme,cytochrome c oxidase, succinate dehydrogenase,citrate synthase, alanine aminotransferase,esterase, superoxide dismutase, catalase, acidphosphatase as well as acetylcholinesterase(brain) were measured by means of establishedenzyme assays. In parallel studies, loach andbrown trout sampled from corresponding fieldsites were investigated to elucidate therepresentativeness of a stream bypass system.Although the episodic exposure scenarios ineither natural stream resulted in considerablevariability of enzyme activities, biochemicalchanges in both species allowed a cleardiscrimination between the two differentlypolluted streams. Similarities in changes ofenzyme activities between fish exposed in thebypass system and the field reached levels of63% and 73.1% in brown trout and loach,respectively. In conjunction with biomarkersfrom other studies, alterations in metabolicenzyme activities were able to serve as a toolfor the sensitive identification ofenvironmental pollutants, which in turn form fromthe basis for an improved understanding ofunderlying toxic processes and an interpretationof toxicant-related effects.     

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.     

Using indicators of fish health at multiple levels of biological organization to assess effects of stream pollution in southwest Germany

The health of fish populations and assemblagesin two degraded streams in south-westernGermany were investigated in order to validatethe use of biomarkers for the assessment ofsmall streams as part of the Valimar project.In the more severely polluted stream,recruitment was impaired and populationabundances were low. Extinction ofsite-specific species and appearance of nonsite-specific species has resulted in a shiftin the species composition from thatcharacteristic of unpolluted reference streams.In the less severely degraded stream, abundantrecruitment and relatively high densities ofadults indicated healthy, self sustaining fishpopulations. Missing species, however,indicated some effects of human influenceswithin the reference stream. The reproductivestatus of adult stone loach, Barbatulabarbatula, was not affected in any stream asreflected by normal production of eggs andreproductive behavior. Indices of energystorage differed between the investigated sitesbut could not be related to pollution. Theevaluation of biological integrity based onfish assemblages revealed that both sites inthe more severely impacted stream were in poorcondition. The two reference sites wereclassified in moderate and good condition,respectively. By excluding effects of migrationbarriers on the fish assemblage there was astronger correlation between chemical waterquality and biomarker responses. The resultsindicate the importance of assessing theeffects of pollution within the content oflongitudinal gradients in streams and theusefulness of measuring health effects overseveral levels of biological organization.     

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.     

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.     

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.     

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.     

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.     

Spatial variation in density of stream benthic fishes in northern Hokkaido, Japan: does riparian vegetation affect fish density via food availability?

The densities of two benthic fishes, the Siberian stone loach (Noemacheilus barbatulus) and the wrinklehead sculpin (Cottus nozawae), and the biomass of their food resources (i.e., periphyton and benthic invertebrates) were compared between forest and grassland streams in northern Hokkaido, Japan, to examine whether riparian deforestation had positive effects on the benthic fishes via enhancement of food availability. The comparisons indicated that riparian vegetation had little influence on periphyton, invertebrates, or fishes. Regression analysis indicated that spatial variations in loach and sculpin densities were explained more by substrate heterogeneity, competitor abundance, or both, rather than by food abundance. However, when the two species were combined as benthic insectivores, a strong correlation was found between total benthic fish density and invertebrate biomass. Our results suggest that, although total benthic fish abundance was food limited, riparian vegetation had no positive effects via food availability on the benthic fishes in our streams.     

The utility of naphthyl-keratin adducts as biomarkers for jet-fuel exposure

We investigated the association between biomarkers of dermal exposure, naphthyl-keratin adducts (NKA), and urine naphthalene biomarker levels in 105 workers routinely exposed to jet-fuel. A moderate correlation was observed between NKA and urine naphthalene levels (p?=?0.061). The NKA, post-exposure breath naphthalene, and male gender were associated with an increase, while CYP2E1*6 DD and GSTT1-plus (++/+?) genotypes were associated with a decrease in urine naphthalene level (p?<?0.0001). The NKA show great promise as biomarkers for dermal exposure to naphthalene. Further studies are warranted to characterize the relationship between NKA, other exposure biomarkers, and/or biomarkers of biological effects due to naphthalene and/or PAH exposure.     

The critical thermal limits for the stone loach, Noemacheilus barbatulus, from three populations in north-west England

1. The chief objective was to determine the upper and lower thermal limits for feeding and survival in the stone loach, Noemacheilus barbatulus, using juveniles (total length 30–45 mm, live weight 0.25–0.80 g) from one population and adults (total length 77–100 mm, live weight 3.6–7.9 g) from three populations. 2. Fish were acclimatized to constant temperatures of 3, 7, 10, 15, 20, 25 and 27°C; then the temperature was changed at a rate of 1°C/30min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1°C/30min was the optimum value from preliminary experiments, using nine rates from 0.5°C/48h to 18°Ch^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values of 28.0 ± 0.15°C and 5.1 ± 0.55°C for adults, 25.0 ± 0.54°C and 6.1 ± 0.92°C for juveniles. Incipient lethal levels defined a tolerance zone within which stone loach survive for a considerable time; upper limits increased with acclimation temperature to reach a maximum plateau of 29.1 ± 0.18°C for adults and 29.0 ± 0.40°C for juveniles; lower limits also increased from near 0°C to 3.0 ± 0.40°C for adults and juveniles. Upper limits for the ultimate lethal level increased with acclimation temperature to a maximum plateau of 33.5°C for adults (95% CL ± 0.19) and juveniles (95% CL ± 0.40), whilst the lower limits increased from near 0°C to 2.5 ± 0.30°C. At acclimation temperatures below 20°C, upper incipient and ultimate lethal values were significantly lower for juveniles than those for adults. 4. The thermal tolerance of stone loach was higher than that of juvenile Atlantic salmon or brown trout, one or both of these species often being dominant in streams with stone loach.     

Brown trout Salmo trutta f. Fario liver ultrastructure as a biomarker for assessment of small stream pollution

T he effects of environmental pollutants from two small streams in south-west Germany on the liver of brown trout (S almo trutta f. Fario ) were studied as biomarkers by means of quantitative and semi-quantitative electron microscopy, and quantitatively by morphometrical measurements. Cellular damage was assessed semi-quantitatively based on a classification of ultrastructural responses. Both methods revealed more severe cellular effects in the liver of trout which had been exposed to the highly polluted stream than in those exposed to the lightly polluted river. Morphometrical studies showed a significant reduction of glycogen storage and a significant increase in number of mitochondria, peroxisomes and cisternae of the endoplasmic reticulum. The biomarker responses of this study were correlated with the results obtained by limnological and analytical investigations, and reflect the levels of pollution in each stream.     

Chemical analyses of water, sediment and biota in two small streams in southwest Germany

As a component of the VALIMAR project a comprehensive chemicalanalysis study was conducted in two small streams, the Körsch andthe Krähenbach, in southern Germany. The investigated pollutantswere heavy metals (HM), polycyclic aromatic hydrocarbons (PAHs),polychlorinated biphenyl's (PCBs) and a set of 33 pesticides.Samples from stream water, sewage treatment plant effluents,stream sediment and fish were analyzed. In the stream water, HMand PAHs showed slightly higher concentrations in the Körsch thanin the Krähenbach, whereas the pesticide concentrations (mainlyplant protective agents) were significantly higher in the Körschthan in the Krähenbach. Because of their similar occurrence andconcentrations in the Körsch water and in the sewage treatmentplant effluent, it appears that most of the pesticides wereintroduced into the river via the sewage treatment plant. Only inthe cases of terbuthylazine, triallate, chlorfenvinfos,metazachlor and mecoprop were the occurrence and concentrationsin the Körsch higher suggesting that run-off was the mostimportant route for these five compounds in this stream.The sediments of the two streams clearly differed in terms ofpollutant concentration. Polycyclic aromatic hydrocarbons, PCBsand HM were found in slightly higher concentrations in the Körschthan in the Krähenbach whereas pesticide concentrations weresignificantly higher in the Körsch. Results of each samplingdemonstrated extreme variations, due to frequent high-watersituations that led to high turnover and wash out of thesediment. In the sediment samples, most of the detected compoundswere more lipophilic than were those detected in water.Brown trout (Salmo trutta f. fario) and loach (Barbatulabarbatula) were sampled directly from the natural streams, from astream water fed bypass exposure system, and from a controlsystem in the laboratory. In the case of PAHs, PCBs andpesticides, concentrations were higher in fish exposed to theKörsch water than to the Krähenbach water. Heavy metals did notdifferentiate between the two streams. Polychlorinated biphenylsand pesticides showed higher concentrations in fish from thefield, which can be explained by longer exposure periods. Incontrast, PAHs showed the lowest concentrations under fieldconditions. Polycyclic aromatic hydrocarbons were possiblydisplaced by other compounds of high concentration. The pesticidepatterns in trout were quite similar in the different exposuretypes with primarily lindane, PCP and trifluraline contributingto these pattern changes. In loach, larger variations in allcontaminant concentrations were found but the same threecompounds also contributed most to the observed pattern changes.The analytical results were compared with various internationalobjective values for a good water quality as well as with valuesfrom other studies concerning the pollutant concentrations ofsediment and fish. All collected chemical data form a basis forthe biomarker investigations conducted by the other participantsof the VALIMAR project in order to find correlations betweenbiomarker responses and chemical pollution data of the twostreams.     

Major depressive disorder: insight into candidate cerebrospinal fluid protein biomarkers from proteomics studies

Introduction: Major Depressive Disorder (MDD) is the leading cause of global disability, and an increasing body of literature suggests different cerebrospinal fluid (CSF) proteins as biomarkers of MDD. The aim of this review is to summarize the suggested CSF biomarkers and to analyze the MDD proteomics studies of CSF and brain tissues for promising biomarker candidates.

Areas covered: The review includes the human studies found by a PubMed search using the following terms: ‘depression cerebrospinal fluid biomarker’, ‘major depression biomarker CSF’, ‘depression CSF biomarker’, ‘proteomics depression’, ‘proteomics biomarkers in depression’, ‘proteomics CSF biomarker in depression’, and ‘major depressive disorder CSF’. The literature analysis highlights promising biomarker candidates and demonstrates conflicting results on others. It reveals 42 differentially regulated proteins in MDD that were identified in more than one proteomics study. It discusses the diagnostic potential of the biomarker candidates and their association with the suggested pathologies.

Expert commentary: One ultimate goal of finding biomarkers for MDD is to improve the diagnostic accuracy to achieve better treatment outcomes; due to the heterogeneous nature of MDD, using bio-signatures could be a good strategy to differentiate MDD from other neuropsychiatric disorders. Notably, further validation studies of the suggested biomarkers are still needed.     

A functional model for maximum growth of immature stone loach, Barbatula barbatula, from three populations in north-west England

1. The chief objective was to develop a functional model for growth of stone loach, Barbatula barbatula, using immature fish from three populations. The growth model had been developed previously for brown trout, Salmo trutta, but new estimates of the five parameters for the stone loach had to be obtained from laboratory experiments. 2. Fish from four size groups (initial arithmetic mean live weights 0.053 g, 0.231 g, 0.840 g, 1.612 g, with five fish per group) from Great Oaks Wood Beck were acclimatized to constant temperatures of either 3, 5, 10, 15, 20 or 25 °C. Each fish was kept in a separate tank and fed to satiation on freshwater shrimps. Weights and lengths of each fish were recorded at the start and finish of a growth period of 35 days. For each of the other populations (Black and Ford Wood Becks), there were only three temperatures (5, 10, 20 °C) with ten fish per temperature. 3. The growth model was an excellent fit (P < 0.001, R² > 0.99) for the 120 fish from Great Oaks Wood Beck. Growth rates were negative at 3 °C, close to zero at 5 and 25 °C, and positive at 10, 15 and 20 °C, with an optimum value of 19 °C. When growth rates were positive, they decreased markedly with increasing fish weight for small fish but decreased more slowly for larger fish. At the start of the experiments, weight–length relationships were similar for fish from all three populations and were well described by a power function. There was excellent agreement between growth rates estimated from the fitted growth model for fish from Great Oaks Wood Beck and values obtained for fish from Black and Ford Wood Becks. Data from all three populations were therefore pooled (n = 180) to obtain new estimates of the five parameters in the model. 4. Comparisons between parameter estimates for trout and stone loach showed that the latter grew better in warmer waters (e.g. optimum value for growth was 19.0 °C for stone loach and 13.1 °C for trout, with ranges for growth of 5.0–25.0 °C and 3.6–19.5 °C, respectively).     

Fish abundance and habitat relationships in forest and grassland streams, northern Hokkaido, Japan

The relationships between habitat variables and population densities of masu salmon (Oncorhynchus masou), rosyface dace (Leuciscus ezoe), Siberian stone loach (Noemacheilus barbatulus) and wrinklehead sculpin (Cottus nozawae) were examined by data collected at 55 reaches in forest and grassland streams in northern Hokkaido, Japan. Regression analysis suggested that salmon and dace densities were affected by water temperature (negative for salmon, positive for dace) and structural habitat factors (woody debris for salmon, pools for dace). Salmon density was higher in forest reaches than in grassland reaches, whereas dace density was higher in grassland reaches, suggesting that the removal of riparian forest had raised water temperature and allowed upstream invasions by dace. In contrast to salmon and dace, neither the density of loach nor sculpin differed between the forest and grassland reaches. For their densities, a negative effect of each on the other was most important, suggesting a strong effect of interspecific competition between loach and sculpin on their distributions. However, regression models also suggested that substrate heterogeneity mediated the outcome of their interspecific competition. On the basis of the results, a scenario is predicted for a fish-assemblage change with a typical land-development process in Hokkaido, and the importance of leaving or restoring riparian buffer for conservation and restoration of stream habitat is emphasized.     

Spatial and ontogenetic variability in the microhabitat use of stream-dwelling spined loach (Cobitis taenia) and stone loach (Barbatula barbatula)

Ontogenetic and spatial variability in microhabitat use of spined loach Cobitis taenia (Linnaeus), considered as one species for the purposes of this study, and stone loach Barbatula barbatula (Linnaeus) were examined in the River Great Ouse basin, England, using multivariate and habitat suitability methods, including a technique for handling spatial variation in collections of preference curves. Distinct ordinations of spined age classes and stone loach developmental stages, respectively, in canonical correspondence analysis of species × variables × samples relationships suggest that the two species occupy completely different microhabitats; however, young‐of‐the‐year spined loach occurred more often than expected with all developmental stages of stone loach except young larvae. Water velocity and filamentous algae were the most influential microhabitat variables, the latter decreasing in importance with increasing age of both fish species. Preferred water velocities generally decreased with age in spined loach and increased in stone loach, with substratum size generally increasing with fish age in both species. Spatial variation in microhabitat preferences was great in both species but less so in the spined loach, suggesting that limited plasticity in habitat use could account, at least in part, for the latter species’ limited distribution and abundance in the catchment. Preference curves for a species, if generated and verified for all life intervals and all seasons, could be used as a management tool for a given stream or sector of river basin. But preference curves should be generated for each location to ensure that river management decisions with regard habitat and species conservation consider local‐level species requirements. Thus, a multi‐(eco)species and multi‐scale approach is required in habitat suitability assessments.