Microsatellite DNA Polymorphism in Intensely Enhanced Populations of Sea Trout (Salmo trutta) in the Southern Baltic

Sea trout (Salmo trutta) is an anadromous form of brown trout, a commercially important salmonid species in Europe. Stocking has been used to compensate for the decrease of natural populations and maintenance of fishery and angling catches. Over 1.5 million smolts and 4.5 million alevins are released to Polish coastal rivers each year. Variation at 7 microsatellite loci (Ssa197, Ssa171, Ssa85, Str15, Str73, Str591, and Str543) was used to study genetic polymorphism of spawners returning to 6 rivers. Application of distance method for comparison of pairs of populations based on number of different alleles (F _ST) revealed significant differences between Vistula and Wieprza, and Parseta as well as between Drweca and Wieprza, and Slupia. The level of heterozygosity was similar between most of the studied sea trout populations; considerable differences were found only for Str591. Differences in frequencies of a few alleles between populations were observed. An exact test of sample differentiation based on allele frequencies confirmed lack of significance of differentiation between the 6 pairs of populations (F _ST and R _ST). No admixture was observed in the studied populations. Possible effects of stocking on the genetic polymorphism of the sea trout populations in wild with implications for biotechnology are discussed.     

A Highly Polymorphic Plasma Protein Locus in Brown Trout (Salmo trutta L.) Populations from Portugal

Genetic polymorphism of an unidentified plasma protein (PX) is described for the first time in Salmo trutta (L.) by means of isoelectric focusing. The analysis of 414 individuals from different geographic origins in Portugal allowed the identification of nine alleles. Heterozygosity in natural populations is generally above 0.60, thus giving similar values to those reported for brown trout microsatellite loci. Substructuring of Portuguese brown trout is evident between northern and southern basins. Genetic affinities between the southernmost rivers and the hatchery stock were detected, suggesting the existence of recent stocking influences.     

A Bioenergetic Analysis of Factors Limiting Brown Trout Growth in an Ozark Tailwater River

We examined prey utilization and energy consumption by brown trout, Salmo trutta, in a cold tailwater (Little Red River, Arkansas, USA; LRR) having low biodiversity and low availability of fish as prey. Stomach content analysis and age estimation were performed on thirty brown trout (10 each of three size classes for a total of 710 trout) collected monthly from an upstream and downstream site over a 1-year period. Diet diversity was low at both sites, as 80% and 70% of all prey consumed by upstream and downstream brown trout, respectively, were isopods. Piscivory (<0.5% of individuals sampled) and consumption of terrestrial invertebrates were rare. There was no relation between diet diversity and trout age, and a very small ontogenetic shift in brown trout diet. Second, we investigated brown trout growth rates relative to prey consumption and temperature. Temperatures and availability of prey were less than required for maximal trout growth. However, prey availability limited trout growth directly, but sub-optimal temperatures probably buffered the effect of this reduced energy consumption by reducing metabolic energy expenditures. Brown trout growth was 54.8–57.0% of the maximum predicted by a bioenergetics model. Instantaneous growth rates for age 1 and adult brown trout were slightly higher for those downstream (0.195) versus those upstream (0.152). Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna and subsequent lack of establishment of cold-tolerant forage fish species due to the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major barrier to brown trout growth.     

Allozymes,mtDNA and microsatellites study introgression in a stocked trout population in France

A comparative study of disturbed (downstream) and undisturbed (upstream) populations in a French Mediterranean river (the Sorgue) was conducted to assess the fate of introgressing hatchery-genes in the aboriginal gene pool. Variation was assessed at 27 protein-coding loci, three microsatellite loci and two mtDNA restriction sites. The results were compared to those from another Mediterranean drainage basin (that of the river Orb). The genetic pattern observed among markers and drainage basins was found to be noticeably different. A reduction in population size is hypothesized to explain the lower variability observed in the upper part of the river Sorgue. Estimations of hatchery gene flow were different between loci but in the same range of values between markers.     

Long-term effects of nutrient enrichment on the condition and size-structure of an alpine brown trout population

Long-term effects of nutrient enrichment on a population of brown trout inhabiting a small, alpine lake in north-central Sweden have been studied for nearly 20 years. The study took place between 1981 and 1999 starting up between 1982 and 1987 with full nutrient enrichment of phosphorus and nitrogen in a ratio by weight of 1:8, followed by a period of reduction by half between 1988 and 1994, and thereafter no enrichment at all. Growth of the brown trout population was low before the application of nutrients. Fertilization promoted the development of zooplankton in great abundance, which gave rise to abundant food for the trout. Already during the first year of nutrient addition the average 4+ and 5+ fish had increased in weight by nearly 50% and in length by about 30%. Maximum growth was reached 5–6 years later—weight by about 175% and length by about 50% higher than before application. The slope of the growth curves for fish of ages 2+ to 5+ increased significantly from 1981 to 1987, and so did the size-variation with a high proportion of the fish reaching larger size. After each change in nutrient treatment the mean weights of 5–6-year-old trout were maintained for about 3 years. Five years after termination of fertilization growth was nearly back to the original state. Although badly needed, long-term studies of fish populations like this are few in the literature.     

Trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) mitochondrial DNA polymorphism in the centre of the marble trout distribution area

The marble trout, a lineage of the Salmo trutta complex, is endemic to the Southern Alpine region. Although it is endangered throughout its entire distribution range, population genetic data were lacking for the central area, including the upper Etsch/Adige River system (South Tyrol, Northern Italy). A total of 672 Salmo trutta specimens, comprising phenotypic marble trout and phenotypic brown trout, from 20 sampling sites throughout South Tyrol were analysed by sequencing the complete mitochondrial DNA control region. Thirteen distinct haplotypes were identified, which clustered within three major genetic lineages: the Marmoratus (MA), the Atlantic (AT) and the Danubian (DA) lineage. 41.7% of the investigated individuals carried haplotypes of the MA lineage, 47.9% of the AT lineage and 10.4% of the DA lineage. It is noticeable that AT haplotypes were present at all sampling sites and no “pure” marble trout population with exclusively MA haplotypes was found. This points to a considerable impact of stocking with allochthonous brown trout, given that there is no evidence for natural colonisation by individuals of the AT lineage. However, our data indicate, for at least four localities, a limited gene flow between the native marble trout and hatchery-reared strains. Future conservation and rehabilitation measures will thus have to concentrate on the identification of remnant pure marble trout individuals from such mixed populations. Handling editor: C. Sturmbauer     

A population analysis of Robertsonian and Ag-NOR polymorphisms in brown trout (Salmo trutta)

An analysis of Robertsonian polymorphism and variation in the number of active NORs has been carried out in several populations of brown trout (Salmo trutta) from Northwestern Spain. The karyotype of this species appears to be soundly established, and essentially no variation has been found in chromosome number. Interindividual and interpopulation variation in arm number was detected, with figures ranging between 100 and 102 among individuals, and between 100.10 and 100.80 among populations. This variation in arm number is solely attributable to the polymorphism of the short arm of the main NOR-bearing pair 11, which can appear from acrocentric to metacentric in different individuals. Most populations analyzed showed the standard distribution of active NORs previously observed in this species. The Miño drainage basin, and specially the Chamoso population, showed a multi-chromosomal distribution of active NORs, with several new locations, always telomeric. In most cases no concordance was observed between previously detected rDNA sites in S. trutta and the new Ag-NOR locations. This fact suggests a transposition mechanism rather than an activation of silent rDNA sites to explain this multichromosomal NOR pattern.     

Genetic introgression between wild and stocked brown trout in the Douro River basin, Spain

The genetic diversity of Spanish brown trout is currently threatened by stocking with exogenous brown trout from Central and Northern Europe. In the Douro River basin 25% of the analysed populations in the present study showed introgression by genes of hatchery origin. The mean introgression estimated by the single locus approach ( S ) varied from 0 to 22% among populations, with a mean value of 3%. The hatchery allele markers were absent in populations where stocking ceased in 1993. However, the introgression effect was observed in all populations stocked until 1998. It seems that cessation of stocking is a good measure for restoring native populations. A thorough review of published and present data of genetic interactions between wild and stocked brown trout in Spanish rivers indicates different levels of introgression between basins. The absence of a clear geographical pattern in the introgression level suggests that ecological interactions and local stocking programmes may play an important role in stocking success. Finally, several guidelines are provided for conservation and management of native brown trout populations in Spanish rivers.     

Special traits of biology and of the parasite fauna of juvenile salmonid fish of the genus <Emphasis Type="Italic">Salmo</Emphasis> of the Tornio River system (The Baltic Sea basin)

Juveniles of Atlantic salmon Salmo salar and trout S. trutta populating the system of the Tornio River (the Baltic Sea basin) are investigated. The obtained parasitological data indicate the absence of rigid spatial and food competition between juvenile salmon and trout in the case of their cohabitation.     

Temporal variations in the diet of brown trout (Salmo trutta L.) and rainbow trout (S. gairdneri R.) in Rutland Water

The diet of brown trout (Salmo trutta L.) and rainbow trout (S. gairdneri Richardson) in Rutland Water were compared during the first two fishing seasons (April–October 1977 and 1978).Fortnightly samples of approximately forty stomachs were obtained from boat and bank, rod-and-line caught trout giving a total of 1046 stomachs over the two seasons.During 1977 seasonal changes in the diet were divided into two phases; the first being a period of abundant drowned terrestrial food until June. This was followed by a period of more stable water level from July onwards when chironomid larvae and pupae were consistently the most important food items and the diversity of food also increased.In 1978 the proportion of chironomid pupae and larvae declined and they were replaced in the diet by Gammarus and Asellus.     

The selection of the ‘wild’: A combined molecular approach for the identification of pure indigenous fish from hybridised populations

The identification of pure indigenous fish from hybridised populations represents a key issue in fisheries management and conservation biology. In the present study an approach for selection of purebred marble trout (Salmo trutta marmoratus C.) individuals out of admixed populations was set up and assessed. In a first step, baseline data sets of pure marble trout and pure brown trout specimens based on twelve microsatellite loci were used to simulate five consecutive generations of admixture. The baseline and the resulting simulation data sets were then combined with data of a ‘real’ hybridised marble trout population to perform a single individual assignment test as implemented in STRUCTURE. By this procedure the assignment approach was calibrated and it was possible to compare admixture coefficients obtained for individuals from different populations. The ranking of individual admixture coefficients on a plot and comparison with simulated data revealed that the test population was composed of pure marble trout individuals, first generation hybrids between marble trout and brown trout, and hybrid backcross specimens between both groups. However, by defining a critical q-value of 0.1 and additionally integrating individual sequence data of the mtDNA control region, it was possible to indicate individuals, which could be selected for the establishment of a pure marble trout strain.     

Hybridization between genetically modified Atlantic salmon and wild brown trout reveals novel ecological interactions

Interspecific hybridization is a route for transgenes from genetically modified (GM) animals to invade wild populations, yet the ecological effects and potential risks that may emerge from such hybridization are unknown. Through experimental crosses, we demonstrate transmission of a growth hormone transgene via hybridization between a candidate for commercial aquaculture production, GM Atlantic salmon (Salmo salar) and closely related wild brown trout (Salmo trutta). Transgenic hybrids were viable and grew more rapidly than transgenic salmon and other non-transgenic crosses in hatchery-like conditions. In stream mesocosms designed to more closely emulate natural conditions, transgenic hybrids appeared to express competitive dominance and suppressed the growth of transgenic and non-transgenic (wild-type) salmon by 82 and 54 per cent, respectively. To the best of our knowledge, this is the first demonstration of environmental impacts of hybridization between a GM animal and a closely related species. These results provide empirical evidence of the first steps towards introgression of foreign transgenes into the genomes of new species and contribute to the growing evidence that transgenic animals have complex and context-specific interactions with wild populations. We suggest that interspecific hybridization be explicitly considered when assessing the environmental consequences should transgenic animals escape to nature.     

Combined Assessment of Genetic Variability in Populations of Brown Trout (Salmo trutta L.) Based on Allozymes, Microsatellites, and RAPD Markers

Genetic variability within and among four Spanish natural populations of Salmo trutta L. was evaluated on the basis of 25 enzyme loci, 3 microsatellite loci, and 9 randomly amplified polymorphic DNAs (RAPDs). A total of 21 allelic markers were found, 12 of which were reported by microsatellites, whereas enzyme and RAPD accounted only for 6 and 3, respectively. Genetic variation within samples was significantly higher for microsatellites and RAPD than for enzyme loci. Although all methods reported a high degree of allelic heterogeneity among samples, also revealing a high degree of gene diversity, genetic relationships depicted by UPGMA dendrograms closely agreed for all kinds of data. Microsatellite loci appeared to be the most feasible technique when searching for specific alleles for a population or an area, owing to the higher number of allelic variants found. Received July 1, 1998; accepted January 14, 1999     

Fjord migration and survival of wild and hatchery-reared Atlantic salmon and wild brown trout post-smolts

The behaviour of wild (n = 43, mean L_T = 152 mm) and hatchery-reared (n = 71, mean L_T = 198 mm) Atlantic salmon and wild anadromous brown trout (n = 34, mean L_T = 171 mm) post-smolts with acoustic transmitters was compared in a Norwegian fjord system. There was no difference in survival between wild and hatchery reared salmon from release in the river mouth to passing receiver sites 9.5 km and 37.0 km from the release site. Mortality approached 65% during the first 37 km of the marine migration for both groups. There was no difference between wild and hatchery-reared salmon either in time from release to first recording at 9.5 km (mean 135 and 80 h), or in the rate of movement through the fjord (mean 0.53 and 0.56 bl s⁻¹). Hatchery-reared salmon reached the 37 km site sooner after release than the wild salmon (mean 168 and 450 h), but rate of movement in terms of body lengths per second did not differ (mean 0.56 and 0.77 bl s⁻¹). The brown trout remained a longer period in the inner part of the fjord system, with much slower rates of movement during the first 9.5 km (mean 0.06 bl s⁻¹).     

Plasma glucose kinetics and tissue uptake in brown trout in vivo: effect of an intravascular glucose load

The object of the present study was to elucidate whether a glucose load modifies glucose uptake by tissues in brown trout in vivo. By the use of 2-[1,2-³H]-deoxyglucose, plasma glucose disappearance rate and tissue glucose uptake were measured after an intraaortic glucose load of 500 mg·kg^-1 (glucose load group) and under normoglycemic conditions (control). We also attempted to determine whether fasting modifies the glucose load disposal (fasted glucose load group). The procedure used to calculate 2-deoxyglucose uptake by tissues was evaluated, and the levels of 2-deoxyglucose uptake were compared with those of 2-deoxyglucose phosphorylation. Uptake and phosphorylation rates were similar in all tissues, except in brain and heart. In all the groups glucose uptake rates were highest in spleen, kidney, brain and gills, and lowest in red muscle, heart and white muscle. However, white muscle was the main site of glucose uptake on a whole tissue basis. The glucose load led to strong, long-lasting hyperglycemia, in spite of the increases observed in plasma insulin levels and in glucose uptake rate by the whole body (control: 4.9 mol·min^-1·kg^-1; glucose load group: 6.5 mol·min^-1·kg^-1). This higher rate was due to the higher glucose uptake only in white and red muscles (four- and threefold, respectively). Fasting halved the uptake of glucose by both red and white muscles in the load condition. In consequence the use of exogenous glucose decreased with fasting (fasted glucose load group: 5.1 mol·min^-1·kg^-1), causing still longer hyperglycemia.Abbreviations bw body weight - 2DG 2-[1,2-³H]-deoxyglucose - 2DG-P 2-[1,2-³H]-deoxyglucose phosphate - dpm disintegrations per min - FGL fasted glucose load group - GL glucose load group - G-6-Pase glucose-6-phosphatase - LG L-[1-¹⁴C]-glucose - MS-222 3-aminobenzoic acid ethyl ester methanesulphonate salt     

Effects of salmon lice infection and salmon lice protection on fjord migrating Atlantic salmon and brown trout post-smolts

Effects of artificial salmon lice infection and pharmaceutical salmon lice prophylaxis on survival and rate of progression of Atlantic salmon (n = 72) and brown trout post-smolts (n = 72) during their fjord migration, were studied by telemetry. The infected groups were artificially exposed to infective salmon lice larvae in the laboratory immediately before release in the inner part of the fjord to simulate a naturally high infection pressure. Groups of infected Atlantic salmon (n = 20) and brown trout (n = 12) were also retained in the hatchery to control the infection intensity and lice development during the study period. Neither salmon lice infection nor pharmaceutical prophylaxis had any effects on survival and rate of progression of fjord migrating Atlantic salmon post-smolts compared to control fish. Atlantic salmon spent on average only 151.2 h (maximum 207.3 h) in passing the 80 km fjord system and had, thus, entered the ocean when the more pathogenic pre-adult and adult lice stages developed. The brown trout, in comparison to Atlantic salmon, remained to a larger extent than Atlantic salmon in the inner part of the fjord system. No effect of salmon lice infection, or protection, was found in brown trout during the first weeks of their fjord migration. Brown trout will, to a larger extent than Atlantic salmon, stay in the fjord areas when salmon lice infections reach the more pathogenic pre-adult and adult stages. In contrast to Atlantic salmon, they will thereby possess the practical capability of returning to freshwater when encountering severe salmon lice attacks.     

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

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

Effects of six trace metals on calcium fluxes in brown trout (Salmo trutta L.) in soft water

Summary Calcium fluxes were measured simultaneously in brown trout fry maintained in an artificial soft water medium of [Ca] 20 mol·l^-1 and pH 5.6, and exposed to each of six trace metals (Al, Cu, Fe, Ni, Pb, and Zn). The trace metal concentrations represented typical and maximum levels found in acid waters experiencing declining fishery status. In the absence of trace metals, evidence is presented which suggests that ca. 91% of Ca taken up from the external medium was by extraintestinal active transport. Calcium efflux was stimulated by both concentrations of Al, Cu, Fe, and Pb. Efflux was also stimulated by [Ni] 170 nmol·l^-1 and [Zn] 3000 nmol·l^-1. In some cases, response to increased efflux was stimulation of influx. Lack of stimulation of influx resulted in negative net Ca fluxes. Net Ca losses were recorded at both concentrations of Al, Pb, and Ni, lower concentrations only of Fe, and higher concentrations only of Cu and Zn.Abbreviations J _in influx - J _net net flux - J _out efflux Henceforward in this paper, chemical elements are referred to by their chemical symbols rather than by full names     

Reproductive ecology and growth of a population of brown trout (Salmo trutta L.) in an aquifer-fed stream of Old Castile (Spain)

In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha^–1 and 3.6 to 452.9 Kg ha^–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m^–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature.     

Inflammatory response to Dentitruncus truttae (Acanthocephala) in the intestine of brown trout

Brown trout, Salmo trutta L., were infected with the acanthocephalan Dentitruncus truttae with the most affected areas being the anterior (near the pyloric caeca) and middle intestine. The parasite attached with a proboscis which usually penetrated the mucosa, lamina propria, stratum compactum, stratum granulosum and, sometimes, the muscularis layer. Around the parasite's body was an area of inflammatory tissue. At the point of attachment the lamina propria was thickened and the stratum compactum, stratum granulosum and muscularis layer were disrupted by proboscis penetration. Rodlet cells were more numerous in infected fish (P<0.01), and were found in the epithelial layer away from the worm. Infected intestines had larger numbers of mast cells (P<0.01), often in close proximity to, and inside, the blood capillaries and associated with fibroblasts of the muscularis layer and the stratum granulosum. Their migration toward the site of infection was suggested. Intense degranulation of mast cells was encountered in all intestinal layers especially near the parasite's body. Immunohistochemical tests were conducted on sections of intestinal tissue of uninfected and infected fish revealing the presence of met-enkephalin and serotonin (5-HT) in immuno-related cells of the intestine wall. Infected trout had larger numbers of elements positive to met-enkephalin and serotonin antisera. These data provided evidence for the role of the immune system of brown trout in the modulation of the inflammatory response to D. truttae. Results are discussed with respect to host immune response to an intestinal helminth.