Flatworms like it round: nematode consumption by <Emphasis Type="Italic">Planaria torva</Emphasis> (Müller 1774) and <Emphasis Type="Italic">Polycelis tenuis</Emphasis> (Ijima 1884)

To identify the mechanisms whereby substrate embeddedness and water velocity influence Nooksack dace (Rhinichthys cataractae subsp. cataractae) prey capture efficiency, we stocked dace in foraging arenas with varying substrate types over a range of velocities (0, 25, 35 cm s^?1) and measured their efficiency of prey capture. We stocked a known number of mayfly (Ephemeroptera), black fly (Simuliidae), and chironomid (Chironomidae) larvae in each foraging arena and measured the number of invertebrates remaining after 12 h. Foraging efficiency for mayflies was significantly reduced over unembedded substrate, and capture efficiency for all taxa decreased at higher velocities in all substrate treatments. Decreased foraging efficiency indicates that higher velocities may degrade the accuracy of prey strikes, that dace may alter their foraging behavior to reduce energy expenditures at higher velocities, that there is less available foraging habitat within their velocity tolerances, or that invertebrates become more interstitial at higher velocities. Although it is difficult to unambiguously discriminate among these mechanisms with our experimental design, our results suggest that dace are adapted to foraging in low-velocity micro-habitats within the boundary layer, and that their foraging efficiency may be sensitive to both the refuging ability of their prey and velocity and turbulence at their focal point.     

Assemblage-level effects of the introduced peacock hind (<Emphasis Type="Italic">Cephalopholis argus</Emphasis>) on Hawaiian reef fishes

The peacock hind Cephalopholis argus (family Serranidae), locally known as ‘roi’, was introduced from French Polynesia to Hawaii in the mid-twentieth century as a food fish. However, because of its association with ciguatera fish poisoning, it is rarely fished for food. Previous research indicates that roi could have a negative impact on native reef fish assemblages because of their high densities and prey consumption rates. However, it is unclear whether roi add to the cumulative mortality of prey (predation hypothesis), or whether predation is instead compensatory (doomed surplus hypothesis). This study experimentally assessed the effects of roi on reef fish populations through a long-term (5.5 year) predator removal experiment. A Before-After-Control-Impact study design was used to assess changes in fish assemblages following the removal of roi on 1.3 ha of patch reef. Increases in the density of prey-sized fish (<15 cm TL) were observed 18 months after roi removal. However, those effects did not translate into sustained increases in prey. While increases in potential competitors, wrasses (family Labridae), particularly the piscivorous ringtail wrasse Oxycheilinus unifasciatus, were observed on roi-free reefs, the fish assemblage did not diverge substantially in composition. Native reef fish appeared to resist the potential negative impacts of predation by roi, possibly through a refuge in size for some fish families. Management to protect intact fish assemblage size-structure could serve to bolster native resistance to invading species. In considering the threats facing coral reefs, and the possible solutions, roi removal alone will not likely replenish native fishery resources.     

Continued feeding on <Emphasis Type="Italic">Diporeia</Emphasis> by deepwater sculpin in Lake Huron

Monitoring changes in diets of fish is essential to understanding how food web dynamics respond to changes in native prey abundances. In the Great Lakes, Diporeia, a benthic macroinvertebrate and primary food of native benthivores, declined following the introduction of invasive Dreissena mussels and these changes were reflected in fish diets. We examined the diets of deepwater sculpin Myoxocephalus thompsonii collected in bottom trawls during 2010–2014 in the main basin of Lake Huron, and compared these results to an earlier diet study (2003–2005) to assess if their diets have continued to change after a prolonged period of Dreissena mussel invasion and declined Diporeia densities. Diporeia, Mysis, Bythotrephes, and Chironomidae were consumed regularly and other diet items included ostracods, copepods, sphaerid clams, and fish eggs. The prey-specific index of relative importance calculated for each prey group indicated that Mysis importance increased at shallow (≤55 m) and mid (64–73 m) depths, while Diporeia importance increased offshore (≥82 m). The average number of Diporeia consumed per fish increased by 10.0% and Mysis decreased by 7.5%, while the frequency of occurrence of Diporeia and Mysis remained comparable between time periods. The weight of adult deepwater sculpin (80 mm and 100 mm TL bins) increased between time periods; however, the change in weight was only significant for the 80 mm TL group (p?<?0.01). Given the historical importance of Diporeia in the Great Lakes, the examination of deepwater sculpin diets provides unique insight into the trophic dynamics of the benthic community in Lake Huron.     

Size-related dietary changes observed in the squid<Emphasis Type="Italic"> Moroteuthis ingens</Emphasis> at the Falkland Islands: stomach contents and fatty-acid analyses

Dietary composition of the onychoteuthid squid Moroteuthis ingens at the Falkland Islands was related to predator size, as shown by stomach contents and fatty-acid analyses. Comparisons were made between two size classes of squid: those of mantle length <200 mm and those of mantle length >200 mm. Smaller squid had frequently consumed crustaceans and cephalopods; fish were of secondary importance. Larger squid consumed mostly fish and moderate amounts of cephalopods, but had rarely consumed crustaceans. These findings were supported by comparisons drawn between digestive-gland fatty-acid profiles and the fatty-acid profiles of potential prey species. Fatty-acid analyses indicated that the crustaceans Euphausia lucens, Munida gregaria and Themisto gaudichaudii were important prey items of smaller squid, whereas stomach content and fatty-acid analyses indicated that Gymnoscopelus nicholsi of around 100 mm standard length represented much of the fish prey of larger squid.     

Swimming exercise to control precocious maturation in male seabass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>)

Background

Male European seabass, already predominant (~?70%) in cultured stocks, show a high incidence (20–30%) of precocious sexual maturation under current aquaculture practices, leading to important economic losses for the industry. In view of the known modulation of reproductive development by swimming exercise in other teleost species, we aimed at investigating the effects of sustained swimming on reproductive development in seabass males during the first year of life in order to determine if swimming could potentially reduce precocious sexual maturation.

Methods

Pre-pubertal seabass (3.91?±?0.22 g of body weight (BW)) were subjected to a 10 week swimming regime at their optimal swimming speed (U_opt) in an oval-shaped Brett-type flume or kept at rest during this period. Using Blazka-type swim tunnels, U_opt was determined three times during the course of the experiment: 0.66 m s^??1 at 19?±?1 g BW, 10.2?±?0.2 cm of standard length (SL) (week 1); 0.69 m s^??1 at 38?±?3 g BW, 12.7?±?0.3 cm SL (week 5), and also 0.69 m s^??1 at 77?±?7 g BW, 15.7?±?0.5 cm SL (week 9). Every 2 weeks, size and gonadal weight were monitored in the exercised (N?=?15) and non-exercised fish (N?=?15). After 10 weeks, exercised and non-exercised males were sampled to determine plasma 11-ketotestosterone levels, testicular mRNA expression levels of genes involved in steroidogenesis and gametogenesis by qPCR, as well as the relative abundance of germ cells representing the different spermatogenic stages by histological examination.

Results

Our results indicate that sustained swimming exercise at U_opt delays testicular development in male European seabass as evidenced by decreased gonado-somatic index, slower progression of testicular development and by reduced mRNA expression levels of follicle stimulating hormone receptor (fshR), 3-beta-hydroxysteroid dehydrogenase (3βhsd), 11-beta hydroxysteroid dehydrogenase (11βhsd), estrogen receptor-beta (erβ2), anti-mullerian hormone (amh), structural maintenance of chromosomes protein 1B (smc1β), inhibin beta A (inhba) and gonado-somal derived factor 1 (gsdf1) in exercised males as compared with the non-exercised males.

Conclusions

Swimming exercise may represent a natural and non-invasive tool to reduce the incidence of sexually precocious males in seabass aquaculture.

     

A new species of labrid fish <Emphasis Type="Italic">Oxycheilinus samurai</Emphasis> from the western Pacific Ocean

A new species of labrid fish Oxycheilinus samurai sp. nov. is described on the basis of five specimens from the Ryukyu Islands, Japan, and Panay Island, the Philippines. The new species is most similar to the Indo-West Pacific species Oxycheilinus orientalis in having a slender compressed body, 12 pectoral-fin rays, a blackish blotch around the anterior portion of the lateral-line anterior series, and a dark blotch basally on the membrane between the first and second dorsal-fin spines. However, O. samurai can be distinguished from O. orientalis by the following combination of characters: gill rakers 4 + 7–8; snout rounded with maximum circumference 49.8–63.5 % of standard length (SL); interorbital width 7.7–9.2 % of SL; caudal-peduncle depth 13.8–15.3 % of SL; posterior margin of caudal fin white; black or dark red area just before white posterior margin of caudal fin; poorly defined blackish blotches on inner surface of opercle in preserved specimens.     

Suitability of edaphic arthropods as prey for <Emphasis Type="Italic">Proctolaelaps bickleyi</Emphasis> and <Emphasis Type="Italic">Cosmolaelaps brevistilis</Emphasis> (Acari: Mesostigmata: Melicharidae,Laelapidae) under laboratory conditions

Soils are often complex habitats inhabited by a wide range of organisms, some harmful to plants and others beneficial, for example by attacking harmful organisms. Beneficial organisms include predatory mites, some of which have been commercialized for biological control of pest insects and mites. The objective of this work was to evaluate under laboratory condition the suitability of representative soil insect and mite pests, especially Aceria tulipae (Keifer), as prey to the soil-inhabiting predatory mites Proctolaelaps bickleyi (Bram) and Cosmolaelaps brevistilis (Karg). Predation, oviposition and survivorship of recently molted adult females of the predators were assessed in the dark in rearing chambers at 25 ± 1 °C and 75 ± 3% RH. Predation rate by P. bickleyi on A. tulipae was significantly higher than that by C. brevistilis (196.3 vs. 71.0 specimens/day). About 482 A. tulipae were preyed by each P. bickleyi at each day, when 500 A. tulipae were made available daily to the predator. Oviposition rate on that prey was also higher for P. bickleyi (4.2 eggs/day). For C. brevistilis, the highest level of oviposition was on Caliothrips phaseoli (Hood) (1.2 eggs/day). Survivorship was always higher for C. brevistilis (≥ 70%), given its ability to remain alive relatively long even in the absence of prey. High rates of survivorship of P. bickleyi were observed on A. tulipae, Bradysia matogrossensis (Lane) and Protorhabditis sp. Promising results were obtained for P. bickleyi on A. tulipae and even on other prey, justifying the conduction of complementary studies under field condition.     

Age,growth and reproduction of the Asian sheephead wrasse <Emphasis Type="Italic">Semicossyphus reticulatus</Emphasis> in the western Seto Inland Sea,Japan

The Asian sheephead wrasse, Semicossyphus reticulatus, is the largest labrid in temperate waters around Japan. However, the growth pattern of this wrasse remains unclear. Age, growth, and reproduction of S. reticulatus specimens were investigated by sampling in the western Seto Inland Sea, Japan. Opaque ring marks formed on the marginal zone of sectioned otoliths during February–March, suggesting their validity for age estimates. The largest individual was a male, with a standard length (SL) of 591 mm, weight of 8.5 kg, and age of 17 years. Males had significantly larger SLs and older ages than females, and male gonads were histologically confirmed to have secondary testis structures retaining central lumens, suggesting monandric protogyny. The oldest S. reticulatus individual captured was estimated to be a 31-year-old male. The von Bertalanffy growth equation calculated from estimated age and SL was L _t = 489 (1 ? e^{?0.12 (t + 1.75)}), indicating considerably slow growth, particularly after the age of 10 years, which is similar to that of the California sheephead wrasse, Semicossyphus pulcher. The humpheads of S. reticulatus enlarged gradually as their body grew, often resulting in a conspicuous humphead, even in large females.     

Few But Relatively Large Prey: Trophic Ecology of <Emphasis Type="Italic">Chauliodus sloani</Emphasis> (Pisces: Stomiidae) in Deep Waters of the Central Mediterranean Sea

The trophic ecology of Chauliodus sloani (Stomiidae) was thoroughly investigated by stomach content analysis for the first time in the Mediterranean. Overall 206 individuals (64.0–260.0 mm SL) were collected from 2013 to 2015. C. sloani can be defined a specialist predator which feeds exclusively on mesopelagic fish belonging to Gonostomatidae, Myctophidae, Paralepididae, Phosichthyidae, Sternoptychidae and Stomiidae. Gonostomatidae (%IRI = 26.02), Myctophidae (%IRI = 24.77) and Sternoptychidae (%IRI = 24.35) were important food items for C. sloani. Maurolicus muelleri (%IRI = 36.43), Cyclothone braueri (%IRI = 28.26) and Vinciguerria attenuata (%IRI = 12.97) were the most important prey. Cases of cannibalism were also observed. The examination of food size spectrum, in relation to predator length, demonstrated that C. sloani developed a feeding strategy aimed to maximizing energy input and based on the capture of few and relatively large prey: more than 50% of prey items exceeded the value of 20% for ratio between prey and predator size (SL) and the 5.4% of prey measured more than 50% of predator size. Differences in food composition across seasons were found; C. braueri and M. muelleri were more abundant in autumn, V. attenuata during spring. Prey items mainly belongs to weakly vertical migrating fauna, usually concentrated at 400 m Deep Scattering Layer.     

Comparative study of daytime and nighttime sap flow of <Emphasis Type="Italic">Populus euphratica</Emphasis>

In order to quantify and characterize the variance in desert riparian forest tree sap flow, we measured the sap flow from Populus euphratica and compared the daytime and nighttime patterns and responses to environmental variables. Results showed that daytime sap flow velocity was significantly higher (P?<?0.05). Daytime and nighttime mean sap flow velocities were 7.65 and 4.01 cm h^?1 in spring, 21.38 and 9.60 cm h^?1 in summer, and 11.04 and 5.21 cm h^?1 in autumn, respectively. Moreover, results indicated that the stoma remained partially open (15% minimum) throughout the night, providing sufficient evidence for the existance of nighttime transpiration. The vapor pressure deficit (VPD), stomatal conductance (Cs), photosynthetically active radiation (PAR), air temperature (Ta), wind speed (WS), and soil moisture (θ) all had significant positive effects on P. euphratica sap flow velocity (P?<?0.05). Furthermore, the relationship between daytime sap flow velocity and VPD showed clockwise hysteresis, while the relationship between nighttime sap flow velocity and VPD showed counter-clockwise hysteresis. It was evident that PAR and VPD were the key factors impacting daytime sap flow velocity, while Cs and θ were the key factors impacting nighttime sap flow velocity. Furthermore, linear regression results showed that daytime sap flow had a significant positive effect on nighttime sap flow throughout the growing season (P?<?0.05).     

Distribution and diet of demersal Arctic Cod, <Emphasis Type="Italic">Boreogadus saida</Emphasis>, in relation to habitat characteristics in the Canadian Beaufort Sea

Arctic Cod (Boreogadus saida) occur throughout the circumpolar north; however, their distributions at localized scales are not well understood. The seasonal habitat associations and diet preferences across life-history stages of this keystone species are also poorly known, thereby impeding effective regulatory efforts in support of conservation objectives. The distribution of Arctic Cod in the Canadian Beaufort Sea was assessed using bottom trawling in shelf and slope habitats between 20 and 1000 m depths. Highest catch biomasses occurred at 350 and 500 m depth slope stations, coinciding with >0 °C temperatures in the Pacific–Atlantic thermohalocline and Atlantic water mass. Calanus glacialis, Calanus hyperboreus, Themisto libellula, and Themisto abyssorum were identified as key prey species in the diet of Arctic Cod, comprising approximately 86 % of total biomass in guts. Hierarchical cluster analysis with a SIMPROF test identified five statistically significant (p < 0.05) diet groups among gut samples. Arctic Cod shifted from a primarily Calanus diet at shelf stations (<200 m depth) to a Themisto diet in slope habitats (>200 m depth) coinciding with an associated increase in fish standard length with depth. Smaller Arctic Cod fed primarily on Calanus copepods and larger Arctic Cod fed primarily on the larger Themisto species. The habitat and diet associations presented here will inform knowledge of structural and functional relationships in Arctic marine ecosystems, aid in mitigation and conservation efforts, and will enhance our ability to predict the effects of climate change on the local spatial and depth associations of this pivotal marine fish.     

Suitability of Different Prey Aphids on the Growth,Development and Reproduction of <Emphasis Type="Italic">Chrysoperla zastrowi sillemi</Emphasis> (Esben-Petersen) (Chrysopidae: Neuroptera)

The prey preference of polyphagous predator, green lacewing (Chrysoperla zastrowi sillemi (Esben-Petersen)) was evaluated against five prey aphids viz., mustard aphid (Lipaphis erysimi), green peach aphid (Myzus persicae), cabbage aphid (Brevicorynebrassicae), black bean aphid (Aphis craccivora), spirea aphid (Aphis spiraecola) of agriculture importance and compared with eggs of Corcyracephalonica (Stainton). Lacewing larvae preferred Myzus persicae most followed by Brevicorynebrassicae. The highest growth index (8.31), larval survival (94.50 %), larval weight (10.45 mg), pupal weight (8.78 mg), faster multiplication rate (0.051) and fecundity (183.4 per gravid female) of the predator were recorded on M. persicae. However, the chrysopid reared on Corcyra eggs performed best in all biological parameters and fitness, than on aphid preys. This study explores the possibilities of selecting the most suitable prey aphid species for its exploitation as supplement for mass multiplication of chrysopid during off-season or unavailability of Corcyra eggs.     

First documentation of detailed behaviors of endangered adult Sakhalin taimen <Emphasis Type="Italic">Parahucho perryi</Emphasis> in the Bekanbeushi River system,eastern Hokkaido,Japan, using bio-logging and acoustic telemetry concurrently

Behavior of adult Parahucho perryi was examined using bio-logging and acoustic telemetry concurrently in the Bekanbeushi River system, eastern Hokkaido, Japan, in 2009 and 2010. Based on 46.1–87.9 h data from five P. perryi (69.0–80.0 cm fork length) caught from Lake Akkeshi, they used upstream (n = 2), midstream (n = 3), and downstream (n = 4) habitats. Large variability in diel activity and depth occupation existed in each stream habitat; however, fish in the downstream habitat tended to be more active than those in the upper habitats and mainly occupied shallower depths than mean bottom depth in this habitat.     

Gutsy genetics: identification of digested piscine prey items in the stomach contents of sympatric native and introduced warmwater catfishes via DNA barcoding

A major focus of ecology is understanding trophic relationships and energy flows in natural systems, associated food web dynamics and changes in food webs due to introduced species. Predator-prey interactions are often assessed by examining stomach contents. However, partially digested remains may be difficult to accurately identify by traditional visual analysis. Here we evaluate the effectiveness of DNA barcoding to identify digested piscine prey remains in invasive Blue Catfish Ictalurus furcatus, non-native, but established Channel Catfish Ictalurus punctatus and native White Catfish Ameiurus catus from Chesapeake Bay, USA. Stomach contents were examined and piscine prey items were scored as lightly digested, moderately digested or severely digested. A 652 base pair region of the cytochrome c oxidase subunit I (COI-5P) mitochondrial DNA gene was sequenced for each prey item. Edited barcode sequences were compared to locally-caught and validated reference sequences in BOLD (Barcode of Life Database). A large majority of prey items were sufficiently digested to limit morphological identification (9.4 % to species and an additional 12.1 % to family). However, overall barcoding success was high (90.3 %) with little difference among the digestion classifications. Combining morphological and genetic identifications, we classified 91.6 % of fish prey items to species. Twenty-three fish species were identified, including species undergoing active restoration efforts (e.g., Alosa spp.) and commercially important species, e.g., Striped Bass Morone saxatilis, White Perch Morone americana, American Eel Anguilla rostrata and Menhaden Brevoortia tyrannus. We found DNA barcoding highly successful at identifying all but the most heavily degraded prey items and to be an efficient and effective method for obtaining diet information to strengthen the resolution of trophic analyses including diet comparisons among sympatric native and non-native predators.     

Role of areoles on prey abundance and diversity in the hooded pitcher plant (<Emphasis Type="Italic">Sarracenia minor</Emphasis>, <Emphasis Type="Italic">Sarraceniaceae</Emphasis>)

The hooded pitcher plant, Sarracenia minor, is a carnivorous facultative wetland species native to the southeastern USA and is listed as threatened by the state of Florida. Pitchers of S. minor possess white, semitranslucent spots (areoles), which have been hypothesized to aid in the capture of prey (= visual lures) by increasing the amount of light entering the back of the hood, which persuades insects to enter and fall into the base of the pitcher. In this study, the role of the areoles in prey capture abundance and diversity were experimentally investigated under variable lighting conditions in situ. Plants in two populations experiencing different light intensities, which varied in the amount of canopy cover and incident light reaching the plants, were experimentally manipulated by coloring varying percentages of areoles, ranging from 0 to 100 % (in increments of 25 %), with indelible ink. After 2 months, pitchers were collected and dissected to determine the number and identity of prey captured (approximately 18,000 prey were sampled). Although total prey abundance was approximately five times higher at McGirt’s Creek (sunny site) compared to UNF (shaded site), the effect of areoles on prey capture rates and biodiversity was site dependent. Reducing the number of visual lures of plants at the sunny site produced a significant decrease in the number of prey captured, but prey biodiversity (community composition) was unaffected. However, total prey capture was unaffected at the shaded site, while prey biodiversity was negatively correlated with the percent of areoles colored. Results from the current study suggest that areoles conditionally act as visual lures, but their overall importance is dependent on local environmental variables—especially canopy cover and the amount of incident sunlight reaching the plants.     

Hemato-Immunological Responses and Disease Resistance in Siberian Sturgeon <Emphasis Type="Italic">Acipenser baerii</Emphasis> Fed on a Supplemented Diet of <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis>

A feeding trial was conducted to investigate the effects of different levels of dietary Lactobacillus plantarum on hemato-immunological parameters and resistance against Streptococcus iniae infection in juvenile Siberian sturgeon Acipenser baerii. Fish (14.6 ± 2.3 g) were fed three experimental diets prepared by supplementing a basal diet with L. plantarum at different concentrations [1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ colony-forming units (cfu) g^?1] and a control (non-supplemented basal) diet for 8 weeks. Innate immune responses (immunoglobulin (Ig), alternative complement activity (ACH50) and lysozyme activity) were significantly higher in fish fed the 1 × 10⁸ and 1 × 10⁹ cfu g^?1 L. plantarum diet compared to the other groups (P < 0.05). Furthermore, fish fed on various levels of L. plantarum significantly showed higher red blood cell (RBC), hemoglobin (Hb), white blood cell (WBC) and monocyte compared to those of the control group (P < 0.05). At the end of the feeding experiment, some fish were challenged with S. iniae to quantify the level of disease resistance. The mortality after S. iniae challenge was decreased in fish fed a probiotic. These results indicated that dietary supplementation of L. plantarum improved immune response and disease resistance of Siberian sturgeon juvenile.     

Contrasting the early life histories of sympatric Arctic gadids <Emphasis Type="Italic">Boreogadus saida</Emphasis> and <Emphasis Type="Italic">Arctogadus glacialis</Emphasis> in the Canadian Beaufort Sea

The early life stages of Boreogadus saida and Arctogadus glacialis are morphologically similar, making it difficult to assess differences in their ecological niche. The present study documented for the first time the early life stage ecology of A. glacialis, compared it to that of B. saida, and identified the factors separating the niches of the two sympatric species. The 10,565 larval gadids collected in the Beaufort Sea from April to August of 2004 and 2008 were identified to species either directly by genetics and/or otolith nucleus size, or indirectly with a redistribution procedure. Between 8.0 and 8.7 % of all gadids were assigned to A. glacialis. Larvae of A. glacialis were longer at hatch and experienced lower mortality rates than those of B. saida. The two species shared similar spatiotemporal and vertical distributions, hatching season, and growth rate. Under the ice, feeding incidence of B. saida was low (14 %) relative to A. glacialis (88 %). At lengths <15 mm, both species specialized on different prey. The diet of fish >15 mm overlapped (Schoener’s index = 0.7), with Calanus glacialis and C. hyperboreus providing >50 % of the carbon intake of both species. The higher mortality in B. saida may be explained by the smaller size at age from hatching to metamorphosis and a lower under-ice feeding incidence. The early larval stage appears to be the key period of niche divergence between the two species.     

Assessment of movements and habitat use of <Emphasis Type="Italic">Salmo opimus</Emphasis> in Fırnız stream,river Ceyhan of Turkey using radio telemetry techniques

This study was carried out to provide information about movement and habitat use by an endemic Salmonid species (Salmo opimus Turan et al. Ichthyol Explor Freshw 23: 219–236, Turan et al. 2012) in F?rn?z Stream, a tributary of River Ceyhan in Turkey, using manual tracking as a radio telemetry technique. During the study, 19 of the 23 tagged trout were relocated by eight to 20 times (mean: 15 relocations per fish) in F?rn?z Stream. The time between the tracking surveys and relocations varied from 21 to 44 days (mean: 30 days) and the mean distance between relocations was 151 m (26 to 881 m). Tagged trout showed a distribution within a distance of 9350 m in F?rn?z Stream. 95% of the relocations clustered at a distance of 4500 m, while 75 and 50% of them were distributed at a distance of 1935 m and 1488 m, respectively. The linear home range of the individual ranged from 199 to 5087 m (mean 792 m), whereas mean 95% Kernel Density Home Range (KDHR), 75% KDHR, and mean core range (50% KDHR), were 632 m, 477 m and 290 m, respectively. The depths and velocities of the locations where tagged trout occurred varied from 20 to 185 cm (mean depth: 43 cm) and 11 to 240 cm/s (mean velocity: 45.9 cm/s). There was no correlation between fish size and depth and fish size and velocity. Hydropower stations and trout farms negatively affected movement of the brown trout in the stream. The fish passage in F?rn?z Hydropower Station (HPP) is inefficient due to low water mark downstream. Thus, all the obstructions that prevent fish movements must be arranged to enable fish passage in F?rn?z Stream in order to preserve the brown trout population in the stream.