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Salmo Trutta L. (salmo + trutta_l)

Distribution by Scientific Domains
Earth and Environmental Science52%
Life Sciences41%

Kinds of Salmo Trutta L.

  • brown trout salmo trutta l.
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  • trout salmo trutta l.
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    Selected Abstracts

    Environmentally induced migration: the importance of food

    ECOLOGY LETTERS, Issue 6 2006
    Ivan C. Olsson
    Abstract The decision to migrate or not is regarded as genetically controlled for many invertebrate and vertebrate taxa. Here, we show that the environment influences this decision. By reciprocally transplanting brown trout (Salmo trutta L.) between two sections in a river, we show that both migratory and non-migratory behaviour can be environmentally induced; migratory behaviour developed in a river section with high brown trout densities and low specific growth rates, whereas non-migratory behaviour developed in a section with low brown trout densities and high specific growth rates. In a laboratory experiment, we tested the effect of food availability on the development of migratory and non-migratory body morphologies and found that most brown trout became migrants when food levels were low but fewer did so at high food levels. Thus, the decision to migrate seems to be a plastic response, influenced by growth opportunities. [source]

    Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)

    ECOLOGY OF FRESHWATER FISH, Issue 2 2010
    P. Gustafsson
    Gustafsson P, Bergman E, Greenberg LA. Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.).Ecology of Freshwater Fish 2010: 19: 170,177. © 2010 John Wiley & Sons A/S Abstract ,, Terrestrial invertebrate subsidies are believed to be important energy sources for drift-feeding salmonids. Despite this, size-specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ,2+) when fed either benthic- (Gammarus sp.) or surface-drifting prey (Musca domestica) in laboratory experiments. To test for size-specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two-prey experiments also showed that 1+ trout ate significantly more surface-drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ,2+ trout. Analyses of the vertical position of the fish in the water column corroborated size-specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size-specific differences in foraging and vertical position suggest that larger trout may be able to use surface-drifting prey to a greater extent than smaller conspecifics. [source]

    Effect of habitat fragmentation on spawning migration of brown trout (Salmo trutta L.)

    ECOLOGY OF FRESHWATER FISH, Issue 3 2006
    C. Gosset
    Abstract , Human-induced habitat alteration is one of the main causes of the decline of freshwater fish populations. The watershed of the River Bidasoa (Spain) is an example of heavily fragmented habitat. The local brown trout (Salmo trutta L.) population is disturbed, with evidence of poor recruitment as well as low adult densities in the main stem. Forty male and female adult migratory trout were tagged with external or internal radio transmitters and released. Fixed stations with data loggers and mobile antennae were used with daily surveys to track fish movements during the migration and spawning period (3 months). Migration distances did not exceed 10 km, and half of the fish never entered a tributary in the study area. Fragmentation because of weirs on the main stem apparently prevented fish from reaching their spawning destination. Fish that entered the tributaries were first confronted with an accessibility problem because of low discharge. However, each fish chose one tributary, without making attempts to run up in other tributaries. Once in the tributary, fish were restrained in their upstream movements by dams. The study area appeared to be isolated from the vast upper part of the watershed. Within the study area, upper parts of tributaries also seemed strongly disconnected from the main stem. This study illustrates the negative impact of river fragmentation on S. trutta migration pattern. Population sustainability can be directly affected through the low availability of spawning grounds for migratory fish. Long-term effects of fragmentation may cause reproductive isolation within watersheds, which in the case of trout also means isolated phenotypic population units. [source]

    Long-term variation in brown trout, Salmo trutta L., stocking success in a large lake: interplay between availability of suitable prey and size at release

    ECOLOGY OF FRESHWATER FISH, Issue 4 2005
    P. Hyvärinen
    Abstract , Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974,1991 and in summer (late June to early July) in 1992,2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series. Resumen 1. Dado lo impredecible que son los resultados de las repoblaciones, se hace necesario conocer los mecanismos que afectan el éxito de los peces soltados para minimizar los riesgos de error en altas inversiones de repoblaciones. Podría existir una ventana óptima para las sueltas que produzca las condiciones más favorables - tales como la ausencia de predadores en la zona de suelta y la disponibilidad de presas apropiadas - bajo las que cualquier pez soltado pueda sobrevivir y generar una producción máxima. El fin de este estudio fue examinar como factores tales como la abundancia de las poblaciones de presas y predadores, y las tasas, tamaños y estaciones de repoblación pueden explicar las variaciones anuales a largo plazo (años 1974,1991) en el éxito de repoblación de Salmo trutta L. en el Lago Oulujärvi (928 km2, Finlandia central). 2. Individuos de S. trutta fueron repoblados en primavera (finales de Mayo , principios de Junio) durante los años 1974,1991 y en verano (finales de Junio , principios de Julio) durante los años 1992,2001. Los resultados de análisis de regresión por pasos mostró que la biomasa de Coregonus albula (L.) adultos (i.e., presas) en el momento de la suelta tuvieron el mayor efecto positivo sobre el éxito de la repoblación en dos períodos: la biomasa de adultos de C. albula en primavera y ambos dos, juveniles 0+ y adultos en verano. Incrementar el tamaño de los peces repoblados tuvo un efecto positivo si los C. albula disponibles en el momento de la suelta fueron solamente adultos (repoblaciones primaverales). La tendencia a incrementar los CPUE-predadores (CPUE combinadas de Esox lucius L., Lota lota (L.), y Stizostedion lucioperca (L.)) a lo largo del periodo de estudio y su efecto negativo sobre el éxito de las repoblaciones de S. trutta sugirió un mayor efecto de la predación sobre la series temporales completas. 3. Concluimos que el momento de la repoblación juega un papel más importante como determinante de la mejor ventana para la repoblación de S. trutta de lagos. Individuos de S. trutta de tamaños <200 g deberían ser repoblados solo si presas de pequeño tamaño (individuos 0+ de C. albula en verano) son también abundantes en el momento y en el área de la suelta. Si las presas disponibles son solos grandes (adultos de C. albula en primavera), el tamaño de repoblación debería ser mayor con individuos de S. trutta claramente mayores de 200 g porque el mayor tamaño amplia el rango de tamaños de las presas disponibles. [source]

    Population genetics of the European trout (Salmo trutta L.) migration system in the river Rhine: recolonisation by sea trout

    ECOLOGY OF FRESHWATER FISH, Issue 1 2005
    A. Schreiber
    Abstract , Allozyme genetics (34 loci) is studied in up to 1010 European trout (Salmo trutta) from the Rhine, Meuse, Weser, Elbe and Danube river systems in Central Europe. Population samples from single collection sites, chiefly small streams (GCG = 0.2126), rather than the divergence of the trout from Atlantic and Danubian drainages (GSG = 0.0711), contributed to the overall gene diversity of GST = 0.2824. Sea trout (n = 164) and brown trout (n = 767) in Atlantic rivers adhere to the same biogeographical stock, but anadromous trout from the Rhine and the Elbe display more genetic cohesion than resident brown trout from the Rhine system alone. Strayers from the Elbe could have founded the recently re-established sea trout population of the Rhine, after a few decades of absence or precarious rarity. Migrants may even connect the Rhine and Elbe stocks by ongoing gene flow. A release,recapture study confirms that all trout in the Rhine belong to one partly migratory population network: Six of 2400 juvenile sea trout released into a tributary of the Rhine were later recorded as emigrants to the Rhine delta, against three of 1600 released brown trout. One migrant had entered the open North Sea, but the other dispersers were recorded in fresh waters of the Rhine delta (Ijsselmeer, Amstelmeer). Stocking presumably elevated both heterozygosity and fixation indices of brown trout, but this effect is subtle within the range of the Atlantic population group. Improved sea trout management in the Rhine, and modifications to brown trout stocking in the upper Danubian area are recommended. [source]

    Effect of brown trout body size on post-stocking survival and pike predation

    ECOLOGY OF FRESHWATER FISH, Issue 2 2004
    P. Hyvärinen
    Abstract,,, A total of 40 (20 age-3 + 20 age-4) radio-tagged hatchery-reared brown trout (Salmo trutta L.) and 40 wild radio-tagged northern pike (Esox lucius L.) were released into a regulated river. Age-3 brown trout were predicted and observed to be highly vulnerable to predation by pike (50% mortality), whereas age-4 brown trout were predicted and observed to enjoy an almost absolute size refuge from predation (5% mortality). Almost half of the fish from both age groups similarly emigrated and survived from the river within 3 days of the release. However, there was a considerable difference in survival between age groups for fish that remained in the river for a longer period. Of these, all except one age-3 brown trout were eaten by pike, whereas all but one age-4 fish survived predation. Resumen 1. Un total de 40 individuos de Salmo trutta (20 de edad-3 y 20 de edad-4) procedentes de piscifactoría fueron marcados con radio-transmisores y 40 individuos de Esox lucius también marcados con radio-transmisores, fueron soltados en un río regulado. Predecimos y observamos que los individuos de edad-3 de S. trutta fueron altamente vulnerables a la predación por Esox lucius (50 % de mortalidad) mientras que los individuos de edad-4 gozaron de refugio de tamaño casi absoluto de la predación (5% de mortalidad). 2. Casi la mitad de los peces de ambos grupos de edad sobrevivieron y emigraron del río durante los tres días siguientes a la suelta. Sin embargo, hubo una considerable diferencia en la supervivencia entre grupos de edad para los peces que permanecieron en el río por un período mayor de tiempo. De estos, todos excepto 1 individuo de S. trutta de edad-3 fueron comidos por E. lucius mientras que todos excepto un individuo de edad-4 sobrevivieron a la predación. [source]

    Effects of size and morphology on swimming performance in juvenile brown trout (Salmo trutta L.)

    ECOLOGY OF FRESHWATER FISH, Issue 4 2003
    A. F. Ojanguren
    Abstract,,, Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout (Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size-corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade-off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size-corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage. [source]

    Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

    ECOLOGY OF FRESHWATER FISH, Issue 1 2003
    A. Klemetsen
    Abstract ,,,Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3,5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour. [source]

    Resource partitioning between lake-dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.))

    ECOLOGY OF FRESHWATER FISH, Issue 4 2000
    L. Jørgensen
    Abstract , Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (,160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (,120 mm) had a higher diet overlap than larger parr (121,160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone., [source]

    Gillnet fishing drives lake-migrating brown trout to near extinction in the Lake Päijänne region, Finland

    FISHERIES MANAGEMENT & ECOLOGY, Issue 2 2010
    J. SYRJÄNEN
    Abstract, Wild stocks of brown trout, Salmo trutta L., collapsed in Finnish inland waters during the 20th Century because dams prevented upstream migration, and low water quality and stream dredging weakened reproduction. The demise in migratory stocks was coupled with overfishing, mainly by gillnetting on lakes. Consequently, the migratory spawning stocks have diminished to negligible levels. The remaining stocks exhibit restricted immigration and emigration, are supplemented by continuous stocking, and their natural genetic diversity is affected by human activities. In recent years, various recovery actions have been implemented including stream channel restorations, fish passage facilities constructed and stocking of eggs and smolts. Gillnetting has also been regulated by banning certain mesh sizes, and catch-and-release of wild trout is spreading amongst sport fishers. However, these measures seem to be inadequate and almost no recovery of migratory populations has been reported. The problem of by-catch in intensive gillnetting continues to threaten stocks and creates disputes between stakeholders. [source]

    The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk stream

    FISHERIES MANAGEMENT & ECOLOGY, Issue 2 2009
    W. D. RILEY
    Abstract, The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels. [source]

    Emigration patterns among trout, Salmo trutta (L.), kelts and smolts through spillways in a hydroelectric dam

    FISHERIES MANAGEMENT & ECOLOGY, Issue 5-6 2008
    M. KRAABØL
    Abstract, The emigration patterns among radio-tagged trout, Salmo trutta L., kelts (n = 41, total length: 60,90 cm) and smolts [n = 27, total body length (BL): 22,30 cm] in the regulated River Gudbrandsdalslågen, south-east Norway, were studied by investigating the influence of sex (kelts) and BL (kelts and smolts) on the timing of emigration. In total, 49% of the kelts emigrated towards the hydroelectric dam shortly after spawning, whilst 51% over-wintered. Female kelts were five times more likely to initiate autumn emigration, and eight times more likely to descend the spillways during the first release of surface water than males. Large individuals of both sexes descended earlier than smaller individuals. Larger smolts were more likely to descend during the first release of surface water than smaller smolts. To safeguard the emigration of iteroparous trout kelts and smolts, the spillways should release surface water both in autumn and spring to avoid selective forces during emigration through spillways. [source]

    Creation of artificial upwelling areas for brown trout, Salmo trutta, spawning in still water bodies

    FISHERIES MANAGEMENT & ECOLOGY, Issue 5 2006
    Å. BRABRAND
    Abstract, Brown trout, Salmo trutta L., spawning sites were constructed by creating areas of artificial upwelling water, 252 ± 37 mL m,2 min,1 (95% CL), through appropriately sized spawning gravel substrate in 3 m2 vessels buried in the bottom of a 150-m2 pond. Natural spawning occurred in the vessels during autumn 2001,2004, with hatching and alevin swim up the following spring. In areas of upwelling, egg survival was 85,95%, while no live eggs were observed in areas without upwelling. In areas with upwelling, the maximum density of live eggs at the eyed stage was 570,1510 eggs m,2. In spring 2004 and 2005, the density of alevins was estimated at 322 (±187) m,2 and 567 (±217) m,2, respectively, in areas with upwelling water, compared with 35.2 ± 25.4 m,2 in areas without upwelling water in 2004. [source]

    Seasonal variation in habitat use by salmon, Salmo salar, trout, Salmo trutta and grayling, Thymallus thymallus, in a chalk stream

    FISHERIES MANAGEMENT & ECOLOGY, Issue 4 2006
    W. D. RILEY
    Abstract, A portable multi-point decoder system deployed in a tributary of the River Itchen, a southern English chalk stream, recorded the habitats used by PIT-tagged juvenile salmon, Salmo salar L., trout, Salmo trutta L. and grayling, Thymallus thymallus L., with a high degree of spatial and temporal resolution. The fishes' use of habitat was monitored at 350 locations throughout the stream during September/October 2001 (feeding period) and January/February 2002 (over-wintering period). Salmon parr tended to occupy water 25,55 cm deep with a velocity between 0.4 and 1.0 m s,1. During both autumn and winter, first year salmon (0+ group) were associated with gravel substrate during the daytime and aquatic weed at night. In autumn, 1+ salmon were strongly associated with hard mud substrates during the day and with marginal tree roots at night. In winter, they were located on gravel substrate by day and gravel and mud at night. Trout were associated with a greater range of habitats than salmon, generally occupying deeper and faster water with increasing age. During the autumn, 0+ trout were located along shallow (5,10 cm) and slow (,0.1,0.4 m s,1) margins of the stream, amongst tree roots by day and on silty substrates at night. During winter the 0+ trout occupied silty substrates at all times. As age increased, trout increasingly used coarse substrates; hard mud, gravel and chalk, and weed at night. All age groups of grayling (0+, 1+ and 2+) tended to occupy hard gravel substrate at all times and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40,70 cm deep with a velocity between 0.3 and 0.5 ms,1, whilst the 0+ groups showed a preference for shallower water with reduced velocity at night, particularly in the winter. There were greater differences in the habitats used between species and age groups than between the autumn and winter periods, and the distribution of fish was more strongly influenced by substrate type than water depth or velocity. The results are discussed in relation to the habitat requirements of mixed salmonid populations and habitat management. [source]

    Characteristics and rehabilitation of the spawning habitats of the sea trout, Salmo trutta, in Gotland (Sweden)

    FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2004
    J.-F. Rubin
    Abstract Characteristics of the natural spawning habitat of sea trout, Salmo trutta L., were studied in Själsöån, a small stream of Gotland, Sweden, from 1992 to 1999. Each year, trout spawned on 17 ± 7 different areas (156 places ha,1). Most of the spawning grounds were used every year. Overcutting was evident for at least 60% of the spawning grounds. Fish spawned on a gravel of 19 ± 7 mm in diameter. From 1978 to 1992, 242 artificial spawning grounds were constructed by the Gotland Sport Fishermen Association in four Gotland streams. A sediment trap was dug upstream to the spawning grounds. The artificial spawning ground comprised of a downstream V-shape stream deflector of large stones with a log weir at the narrowest point of the deflector. Upstream of the dam, 15,60 mm diameter gravel was deposited to constitute the spawning ground substratum. To keep the installation efficient, maintenance is needed every year before the spawning season. [source]

    Evaluation of large-scale stocking of early stages of brown trout, Salmo trutta, to angler catches in the French,Swiss part of the River Doubs

    FISHERIES MANAGEMENT & ECOLOGY, Issue 2 2003
    A. Champigneulle
    Abstract Around 500 000 brown trout, Salmo trutta L., alevins are stocked annually in the 24-km section of the River Doubs under study. All the alevins stocked in the period 1994,1996 were identifiable by fluoromarking their otoliths with tetracycline chlorhydrate. Anglers' catches, between June 1997 and September 1998, comprised trout aged 1+ to 7+ , but most (90% +) were 2+ to 3+ or 4+ , with the majority at 2+ and 3+. There was no significant difference in the size for a given age between marked and unmarked angled trout. The contribution of stocked fish in anglers' catches was around 22% for the 1995 cohort. The contribution of stocking (cohorts 1994 to 1995,1996) to the 1998 catches was around 23% (95% confidence limits: 19,27%). The estimated recapture rate was three to four trout per 1000 alevins stocked for the 1995 cohort. The major contribution (78%) of natural recruitment to anglers' catches suggests that the fishery management based on natural recruitment is still realistic in this part of River Doubs. [source]

    The Irish sea trout enhancement programme: an assessment of the parr stocking programme into the Burrishoole catchment

    FISHERIES MANAGEMENT & ECOLOGY, Issue 6 2002
    C. J. BYRNE
    The success of the sea trout, Salmo trutta L., enhancement programme carried out in the Burrishoole catchment in the west of Ireland from 1993 until 1998 is reviewed in terms of the number of fish stocked, the number of fish which migrated to sea and the number which returned from sea during this period. The success of the programme is also evaluated in terms of the cost of producing parr for stocking and the subsequent value of returning post-smolts (0+ sea age) and rod caught fish. A total of 49 235 tagged fish were released into Lough Feeagh, between 1993 and 1998. Of these fish, 14 788 were microtagged and the remainder, 34 447 had either elastomer or alphanumeric visible implant (VI) tags. Tag loss rates at release varied from 3 to 5.7%. Over the course of the programme a maximum of 7801 fish migrated through the traps towards sea, of which 581, or 7.4%, returned. In any 1 yr a maximum 13.1% of fish returned from sea. The average cost of producing a parr for stocking out was ,1.15, which translated into average values of ,8.16 per smolt and ,169 per returning post-smolt. [source]

    Instream and catchment characteristics affecting the occurrence and population density of brown trout, Salmo trutta L., in forest brooks of a boreal river basin

    FISHERIES MANAGEMENT & ECOLOGY, Issue 6 2001
    E. Jutila
    The occurrence and density of , 1+ brown trout, Salmo trutta L., and their relationship with prevailing instream and catchment characteristics were studied in 50 small forest streams, partially dredged for forest ditching. The occurrence of trout at a stream site was largely determined by the abundance of pools, size of upper catchment and water pH. Moreover, at sites where trout occurred, the abundance of pools was lower at dredged locations than at those in a natural state. In riffles in a natural state, there was a positive relationship between trout density and three instream variables: the abundance of stream pools, cascades and instream vegetation, while an inverse relationship was found with the abundance of substratum of 2,10 cm in diameter. Of the catchment variables, correspondingly, the proportion of forest in the upper catchment was positively related and the proportion of peatland negatively related to trout density. No significant regression model could be fitted for dredged riffles. The possibility of enhancing trout populations in dredged riffles is discussed. [source]

    Survival of sea-water-adapted trout, Salmo trutta L. ranched in a Danish fjord

    FISHERIES MANAGEMENT & ECOLOGY, Issue 4 2000
    S. S. Pedersen
    The effect of seawater adaptation on the survival of coastally released post-smolt trout, Salmo trutta L., was investigated by release: (1) directly (with no adaptation); (2) after retention in net pens in the sea for 29,131 days (delayed release); (3) after feeding with a high-salt diet (12,13.5% NaCl) for 4 weeks; and (4) after a combination of (2) and (3). In total, 17 640 trout (age = 1+, 1.5 and 2+ years; mean fork lengths = 18.2,25.6 cm) were released in 14 batches in the summer or autumn months of 1986,1989. All fish were of domesticated origin and Carlin tagged. Survival and instantaneous mortality rates (total and fishing mortality) were estimated from reported recaptures. Mortality rates were estimated for: (1) the post-smolt period; (2) the period until the legal size of capture (40 cm) was attained; and (3) for larger sea-trout. Release with a delay of 4 weeks gave an increased survival rate. A longer adaptation period did not increase survival. On average, survival was increased by 36%. Survival was not increased by high-salt diets. Until attainment of the legal size for capture, survival was 9.6% higher on average, with extremes as low as 1.7% and as high as 38% in individual batches. [source]

    Maintenance of a small anadromous subpopulation of brown trout (Salmo trutta L.) by straying

    FRESHWATER BIOLOGY, Issue 2 2006
    F. AYLLON
    Summary 1. Microsatellite and isozyme loci variation were used to study structure and dynamics of a brown trout (Salmo trutta) population heavily affected by damming. The downstream area accessible for spawning was drastically reduced to a stream 1 km long influenced by regulated discharge. 2. Stocking of hatchery-reared juveniles failed and the population is entirely supported by anadromous adults from neighbouring populations. 3. Temporal genetic stability is reported here. Some punctual between-river genetic differences are likely because of different contribution from each neighbouring river through years. 4. High anadromy-mediated gene flow produces a lack of genetic substructure in the region. The role of anadromous brown trout on maintenance of endangered small populations is emphasised. [source]

    Genetic structure in Atlantic brown trout (Salmo trutta L.) populations in the Iberian peninsula: evidence from mitochondrial and nuclear DNA analysis

    JOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2000
    S. Dunner
    Summary Brown trout (Salmo trutta L.) was sampled in rivers belonging to three different Spanish basins in order to analyse the distribution of genetic variability. The genetic analysis was performed by using two systems and techniques: nuclear DNA was screened through random amplified polymorphic DNAs (screening 2 × 105 bp of the whole genome), and mitochondrial DNA (mtDNA) through sequencing of the hypervariable control region. Genetic distances between the populations were similar using either analysis although some differences arise. For example, some populations of the Tajo basin were very close through nuclear analysis but more distant using mtDNA. Differences between the two DNA sources could be the result of a different evolutionary rate, and the fact that mtDNA is maternally transmitted and differences in sex migration rates will influence the patterns of genetic variation between the transmitted DNAs. Total variation was partitioned using amova showing a clear subdivision among basins although intrapopulation variation remained as high as 62%. A correspondence analysis defined the differences in a three-dimensional way, clustering the populations according to their common basin. When mtDNA was sequenced, higher variability was noted in the segment between 400 and 600bp of the whole D-loop sequence, suggesting that these 200bp improved the analysis of the variability more than sequencing the t-RNA ends of the control region. A comparison was made between the t-RNAPro ends of the 10 populations screened here and the rest of the published sequences found in the literature, leading to a concentration of these populations in group IV which includes all trouts which originate in the Atlantic. The analyses performed suggest that a high genetic variability is present in all populations and that although there has been a probable interference from stocked strains introduced to increase population density, this was only detectable through the variance between rivers which reflect different policies according to the region where the basin is located. However, the genetic analysis using the two approaches allows the control of the natural populations avoiding a loss of their genetic potential. Zusammenfassung In drei verschiedenen spanischen Wassersystemen wurden Bachforellen (Salmo trutta L.) gesammelt, um die genetische Variabilität zu analysieren. Zur Analyse wurden zwei Systeme und zwei Techniken genutzt: Kern-DNA wurde mittels RAPD analysiert (2.105bp des Gesamtgenoms), mitochondriale DNA durch das Sequenzieren der hypervariablen Kontrollregion. Beide Techniken ergaben ähnliche genetische Distanzen zwischen den Populationen, obwohl Unterschiede bei Populationen aus dem Tajo-Gebiet auftraten, deren Kern-DNA eine sehr geringe Distanz aufwiesen, während die über Sequenzierung von mtDNA ermittelte Distanz auf größere Unterschiede hinwies. Diese Differenz könnte das Ergebnis unterschiedlicher Mutationsraten während der Evolution sein, oder auf dieTatsache zurückzuführen sein, daß mtDNA über die Mutterlinien weitergegeben wird, und Migrationsunterschiede zwischen den Geschlechtern die Muster der genetischen Variation der weitergegebenen DNA-Stücke beeinflußt. Die Gesamtvarianz wurde mit Hilfe von AMOVA analysiert, wobei zwischen den Wassersystemen eine eindeutige Unterteilung festgestellt werden konnte, obwohl die Varianz innerhalb der Population bei 62% liegt. Eine Korrespondenzanalyse erklärt die Distanzen dreidimensional, wodurch die Populationen gleicher Herkunft in Cluster zusammenfallen. Bei der Sequenzierung von mtDNA wurde eine größere Variabilität im Sequenzbereich zwischen 400 und 600 bp der gesamten D-Loop Sequenz festgestellt, was darauf schließen läßt, daß diese 200 bp für eine Analyse der Variabilität geeigneter sind als eine Sequenzierung der t-RNA Enden der Kontrollregion. Ein Vergleich der t-RNAPro Enden der zehn hier untersuchten Populationen und der bereits publizierten Sequenzen führen zu einer Konzentration dieser in der Gruppe IV, zu der alle Forellenpopulationen zählen, die aus dem Atlantik stammen. Die Untersuchung deutet auf eine hohe genetische Variabilität in allen Populationen hin und auf Interferenzen durch Aufstockungsmaßnahmen zur Erhöhung der Populationsdichten hin. Dies ist nur durch die Varianz zwischen den Flußsystemen aufzuklären, die von Region zu Region unterschiedliche Maßnahmen wiederspiegelt. Die genetische Analyse mittels dieser zwei Ansätze erlaubt eine Kontrolle der natürlichen Populationen zwecks Vermeidung eines Verlustes ihres genetischen Potentials. [source]

    Effects of dietary lipid sources on flavour volatile compounds of brown trout (Salmo trutta L.) fillet

    JOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2004
    G. M. Turchini
    Summary The high cost and unpredictable availability of fish meal and fish oil (FO) forced feed mill companies to look for alternative ingredients for aquafeeds. In this study, the effects of alternative dietary lipid sources [FO as control, canola oil (CO), oleine oil (OO), poultry fat (PF) and pork lard (PL)] in trout feed on flavour volatile compounds occurring in brown trout (Salmo trutta L.) fillet were evaluated after 70 days of feeding (rearing temperature 14.6°C). Total amounts of volatile compounds identified were higher for fillets of fish fed diets containing only FO as lipid sources. Total amount of alcohols and aldehydes of the fillets were linearly directly related to the percentage content of polyunsaturated fatty acids (PUFA) n-3 of brown trout flesh. The use of alternative dietary lipid sources, modifying the fillet fatty acids composition, affect the total amount of volatile compounds and, changing the relative amount of each volatile compound, affect the flavour of the fish flesh. [source]

    Genetic divergence between morphological forms of brown trout Salmo trutta L. in the Balkan region of Macedonia

    JOURNAL OF FISH BIOLOGY, Issue 5 2010
    S. Lo Brutto
    The objective of this study was to characterize the genetic structure of two Balkan brown trout morphotypes, Salmo macedonicus and Salmo pelagonicus, and to test whether molecular traits support the species' status proposed by traditional morphological identification. The mitochondrial DNA 12S-rDNA, cyt b and control region genes were sequenced in 15 specimens collected from three localities in the Former Yugoslav Republic of Macedonia. The results of these markers did not support the taxonomic category of species but confirmed the existence of two morphotypes, Salmo trutta macedonicus and Salmo trutta pelagonicus, in the Aegean,Adriatic lineages of the Salmo trutta species complex. [source]

    Cardiac disorders in farmed adult brown trout, Salmo trutta L.

    JOURNAL OF FISH DISEASES, Issue 4 2000
    C Mercier
    During summer in Brittany, France, sea farmed brown trout, Salmo trutta L., regularly experience a high mortality rate which is associated, at least in part, with cardiac disorders (aneurysms and infarcts). The present study is preliminary to a more extensive research programme, the objective of which is to determine to what extent the physiological performance of the cardiovascular system of brown trout is affected by the environmental conditions the fish experience in farm cages. We conducted a 2-week in situ experiment during which the heart rate of eight sea water acclimatized individuals was telemetered using acoustic tags. During the experimental period, water temperature ranged from 16.0 to 17.6 °C. Water oxygen saturation was above 80% at all times and salinity was very high (35.5,) but stable. Although they were unfed and not active, seven of out the eight tagged animals displayed near maximum heart beat frequencies, which ranged between 83 and 98 beats per minute (bpm). On the other hand, the eighth animal exhibited medium-range heart rates (50,70 bpm). Using phase delay maps, we established that the maximum heart rate of brown trout at 17 °C was in the range of 96,100 bpm. This result suggests that in our experimental conditions, the heart rate of most of our inactive fish was between 85 and 100% of maximum myocardial performance. We hypothesize that the cardiac failures observed in brown trout during summer are most likely a result of strenuous workloads imposed on the cardiovascular system by a combination of elevated temperature, high salinity and possibly season-related decreased hypo-osmoregulatory abilities. [source]

    Genetic variation of body size, condition and pyloric caeca number in juvenile brown trout, Salmo trutta L.

    AQUACULTURE RESEARCH, Issue 6 2006
    Jean M Blanc
    Abstract Parental and individual variance components of body length, weight, condition (estimated as the second principal component of the length,weight relationship) and pyloric caeca number were investigated in 6-month-old brown trout (Salmo trutta L.) by the mean of two sib analyses, which provided consistent results. The average heritabilities (±SE) were 0.12 (±0.08) for length, 0.16 (±0.08) for weight, 0.47 (±0.14) for condition and 0.38 (±0.12) for pyloric caeca number. Maternal effects were also observed, although short of significance, in length, weight and caeca number. Correlations between caeca number and body size averaged +0.10 among individuals within lots, but genetic correlations were negative, i.e. about ,0.9 for length and ,0.7 for weight. There was no significant correlation between caeca number and condition. These results lead to question the role that pyloric caeca may play in growth, as well as their usefulness in fish breeding. [source]

    Genetic characterization of naturalized populations of brown trout Salmo trutta L. in southern Chile using allozyme and microsatellite markers

    AQUACULTURE RESEARCH, Issue 7 2003
    N Colihueque
    Abstract This study describes the genetic structure of five naturalized populations of brown trout in southern Chile using allozyme and microsatellite markers to establish levels of intra- and interpopulation genetic variability and divergence. Fourteen enzymatic systems were used comprising 20 loci and three microsatellite loci specific to brown trout. The genetic variability values (allozymes, P=20,35%, average=27%, HO=0.118,0.160, average=0.141; microsatellites, P=33.3,100%, average=66.66%, HO=0.202,0.274, average=0.229) are similar to values described in other naturalized populations of brown trout present in Chile, but higher than those observed in European populations of this species. Values of total genetic diversity (HT) (allozymes=0.1216 and microsatellites=0.3504) and relative genetic divergence (GST) (allozymes=9.5% and microsatellites=15%) were also similar to the results obtained in previous studies of Chilean populations of brown trout. These values, when compared with those obtained in Europe, proved to be similar for HT but lower for GST. The low interpopulational genetic differentiation was in accordance with the small genetic distance observed between the populations analysed (D Nei=0.004,0.025). On the other hand, the high frequency of one of the two alternative alleles of the phylogeographic marker locus LDH-5* in the populations analysed (LDH-5*90>0.84) would indicate a European origin, in particular Atlantic as opposed to Mediterranean, for the brown trout introduced into Chile. The high levels of genetic variability suggest a mixed origin for the naturalized brown trout in Chile, which could have originated either before or during the introduction process. Nevertheless, the low level of genetic differentiation between populations could reflect the short lapse of time in evolutionary terms, during which populations introduced into Chile have been exposed to different evolutionary forces, and which has not been sufficiently long to produce greater genetic differentiation between populations. [source]

    Paternal variation in juvenile survival and growth of the triploid hybrid between female rainbow trout (Oncorhynchus mykiss Walbaum) and male brown trout (Salmo trutta L.)

    AQUACULTURE RESEARCH, Issue 3 2003
    J M Blanc
    Abstract Related sib-groups of rainbow trout × brown trout triploid hybrid and monospecific brown trout controls were obtained from a common set of brown trout sires. On the basis of hybrid juvenile survival and growth, 10 sib-groups were selected and the corresponding brown trouts were raised up to adult stage. Males from each group of brown trout were used to produce a second generation of hybrid progeny, the performances of which were analysed for grandpaternal variation and relation with first generation relatives. Results showed that hybrid traits were influenced by paternal and grandpaternal origin, but that there was little relation between hybrids and brown trouts, or between successive generations of hybrids. [source]