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.     

Food availability and growth rate in natural populations of the brown trout (Salmo trutta) in Corsican streams

The rivers of the island of Corsica, whose catchment areas are on crystalline rock, have low salt contents and their invertebrate fauna is qualitatively and quantitatively poorer than on the European mainland. The growth rate of trout in Corsica was analysed on samples from of six coastal rivers: the Tavignano, the Fium Orbo and the Golo on the west coast, the Prunelli, the Taravo and the Rizzanese on the east coast. Mesological data — conductivity, temperature, calcium content and altitude and biological data — biomass and linear growth rate of the trout, and density of benthic invertebrates — were collected at each of the sampling station.Analysis of variance of the size of three year old trout revealed three groups of rivers. The first includes the Tavignano, the Rizzanese and the Taravo, where the highest linear growth rates were recorded; the second consists of the Golo and the Prunelli, and the third, of the Fium Orbo. Principal component analysis gave two main axes on the basis of temperature and benthic invertebrate density for the first, and trout biomass for the second. Linear regression showed that benthic invertebrate density accounted for 75% of size variance of three year old trout. Evidence of the limiting role of the trophic factor is provided.     

Stock Transfers in Spanish Brown Trout Populations: A Long-term Assessment

Synopsis Stocking of fish from other populations has been commonly employed for enhancement of wild brown trout, Salmo trutta, populations in north Spain. Young hatchery reared brown trout of central European origin were introduced into some Asturian rivers every year since 1984. Based on variation at the isozyme locus LDH-C1* and at the microsatellite locus BFRO 002, two genetic markers race-specific in Salmo trutta, we detected introgression of foreign genomes into native gene pools in some Spanish trout populations where only pure native individuals were present 10 years ago. We strongly suggest development of alternative management policies for conservation of Spanish natural brown trout populations without endangering the traditional recreational fisheries. Jorge I. Izquierdo, Ana G. F. Castillo: These two authors contributed equally to the article.     

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     

Thermoregulatory behavior of brown trout,Salmo trutta

Brown trout, Salmo trutta, were allowed to thermoregulate individually in an electronic shuttlebox. Pooled data for 6 fish showed a diel pattern of preferred temperature, with a diurnal minimum of 10.3°C, an early nocturnal maximum of 13.7°C, a less pronounced mid-scotophase minimum of 11.7°C, and a secondary dawn maximum of 12.8°C, in a somewhat crepuscular pattern. The 24-hour mean preferendum was 12.2°C.     

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.     

Genetic assessment of Atlantic salmon Salmo salar and sea trout Salmo trutta stocking in a Baltic Sea river

Microsatellite DNA variation was used to assess the outcome of stocking Atlantic salmon Salmo salar and migratory trout Salmo trutta in River Sävarå, N Sweden. No information on pre‐stocking genetic composition of S. salar and S. trutta in River Sävarå was available. In 2 year‐classes of S. salar smolt, microsatellite data indicated that post‐stocking genetic composition differed markedly (F_ST= 0·048) from the main donor strain, Byskeälven S. salar, and from other Gulf of Bothnia S. salar stocks (F_ST 0·047 and 0·132). The STRUCTURE programme failed to detect any substructuring within Sävarå salmon. It was concluded that only minor introgression estimated to a proportion of 0·11 (95% CI 0·07–0·16) has occurred in S. salar. Salmo trutta showed overall low differentiation among populations with maximum F_ST of 0·03 making analysis more cumbersome than in S. salar. Still, the SävaråS. trutta deviated significantly from potential donor populations, and STRUCTURE software supported that majority of trout in Sävarå formed a distinct genetic population. Admixture was more extensive in S. trutta and estimated to 0·17 (95% CI 0·10–0·25).     

Effects of sea trout stocking on the population genetics of landlocked brown trout, Salmo trutta L., in the Conwy River system, North Wales, U.K.

The effect of the introduction of fry of anadromous sea trout, Salmo trutta L., on the genetic integrity of landlocked brown trout populations was evaluated. Samples were taken from six brown trout populations from streams above impassable waterfalls in the Conwy river system (North Wales, U.K.) in 1989 and 1990. Three of these streams had no known stocking history and three had been stocked with sea trout fry from the lower Conwy system over the last few years. Representatives of these sea trout were collected from two streams in the lower Conwy system and from a hatchery. Allele frequencies at 13 loci, six of which were polymorphic, were determined by starch gel electrophoresis.
The stocked populations were intermediate in their allele frequencies between unstocked brown trout and sea trout samples. A principal component analysis suggested significant numbers of hybrids in all of the stocked streams. This shows that some of the introduced sea trout did not migrate down the falls to the sea, but stayed in fresh water and hybridized with the local population. The significance of this finding for the conservation of the genetic resource of brown trout stocks is discussed.     

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.     

Localisation of NORs and counterstain-enhanced fluorescence studies in Salmo gairdneri and Salmo trutta (Pisces,Salmonidae)

Summary The karyotypes of the rainbow trout (Salmo gairdneri R.) and the brown trout (Salmo trutta L.) were analyzed by means of silver staining and the chromomycin A₃/distamycin A/DAPI fluorescence banding technique. The nucleolus organizer regions (NORs) were localized at the secondary constrictions of chromosome no. 14 in S. gairdneri and of chromosome no. 10 in S. trutta. Additional silver positive dots were observed at or close to several centromeres in S. gairdneri. Brilliant chromomycin A₃ (CMA₃) fluorescence heterochromatin blocks were localized on both sides of the nucleolar constrictions in S. gairdneri. A polymorphic CMA₃ positive band was detected close to the NORs of S. trutta. No distamycin A/DAPI intense heterochromatin blocks were detected in the genomes of the two Salmo species investigated.     

Managing fish populations under mosaic relationships. The case of brown trout (Salmo trutta) in peripheral Mediterranean populations

Brown trout were collected from 36 locations inthe Iberian Peninsula representing thesouthwestern extreme of this species'distribution in Mediterranean drainages.Allelic distributions among these peripheralpopulations for 26 polymorphic allozyme loci(corrected to remove effects of introgressionfrom exogenous hatchery introductions)indicated a mosaic pattern both within andamong drainages. This distribution wasinterpreted to reflect reticular evolutionaryprocesses involving multiple colonizationepisodes by distinct lineages, secondaryintergradations, and drift. Under thisscenario, management to conserve native genepools differs from that commonly used underhierarchical structures (such as in AtlanticIberian drainages) where geographic patternscould justify regional stocking of indigenousfish in adjacent unsampled areas. Because suchaction risks erosion of native populations inthe present case, remedial efforts should focuson habitat recovery and environmental educationprograms, and harvest sustained by naturalreproduction.     

Glucose metabolism by trout (Salmo trutta) red blood cells

Summary Glucose metabolism has been studied in Salmo trutta red blood cells. From non-metabolizable analogue (3-O-methyl glucose and l-glucose) uptake experiments it is concluded that there is no counterpart to the membrane transport system for glucose found in mammalian red blood cells. Once within the cells, glucose is directed to CO₂ and lactate formation through both the Embden-Meyerhoff and hexose monophosphate shunts; lactate appears as the most important endproduct of glucose metabolism in these cells. From experiments under anaerobic conditions, and in the presence of an inhibitor of pyruvate transfer to mitochondria, most of the CO₂ formed appears to derive from the hexose monophosphate pathway. Appreciable O₂ consumption has been detected, but there is no clear relationship between this and substrate metabolism. Key enzymes of glucose metabolism hexokinase, fructose-6-phosphate kinase and, probably, pyruvate kinase are out of equilibrium, confirming their regulatory activity in Salmo trutta red blood cells. The presence of isoproterenol, a catecholamine analogue, induces important changes in glucose metabolism under both aerobic and anaerobic conditions, and increases the production of both CO₂ and lactate. From the data presented, glucose appears to be the major fuel for Salmo trutta red blood cells, showing a slightly different pattern of glucose metabolism from rainbow trout red blood cells.Abbreviations EM Embden-Meyerhoff pathway - G6D glucose-6-phosphate dehydrogenase - GOT glutamate oxalacetate transaminase - GPI glucose phosphate isomerase - HK hexokinase - HMS hexose monophosphate shunt - IP isoproterenol - LDH lactate dehydrogenase - MCB modified Cortland buffer - OMG 3-O-methyl glucose - PFK fructose-6-phosphate kinase - PK pyruvate kinase - RBC red blood cells - TAC tricarboxylic acid cycle     

Spatio-temporal genetic structuring of brown trout (Salmo trutta L.) populations within the River Luga, northwest Russia

The brown trout populations of the Baltic Sea region have been drastically affected by various human activities during the past century. Due to their propensity to home to their natal site to spawn and their tendency to evolve local adaptations, populations may be genetically differentiated in water systems where no physical barriers preventing interbreeding exist. Consequently, identification of management units, a prerequisite for appropriate conservation and management planning, cannot necessarily be deduced from the physical properties of the habitat. In this study, microsatellite markers were employed to assess the spatio-temporal genetic structuring of inter-connected brown trout populations from a river-system in Northwest Russia. Populations were found to be genetically differentiated from each other (global F _ST 0.06) and the genetic structuring within the river to follow an isolation by distance pattern. Indications of temporal stability were found in some populations, however others appeared to be temporally unstable suggesting differences in the demographic forces affecting the populations. Based on the observed isolation by distance pattern of genetic differentiation, preserving several breeding sites spaced evenly throughout the river-system would appear to be more appropriate than focussing conservation effort on any single stretch of the river. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Enhanced individual selection for selecting fast growing fish: the "PROSPER" method,with application on brown trout (Salmo trutta fario)

Growth rate is the main breeding goal of fish breeders, but individual selection has often shown poor responses in fish species. The PROSPER method was developed to overcome possible factors that may contribute to this low success, using (1) a variable base population and high number of breeders (Ne > 100), (2) selection within groups with low non-genetic effects and (3) repeated growth challenges. Using calculations, we show that individual selection within groups, with appropriate management of maternal effects, can be superior to mass selection as soon as the maternal effect ratio exceeds 0.15, when heritability is 0.25. Practically, brown trout were selected on length at the age of one year with the PROSPER method. The genetic gain was evaluated against an unselected control line. After four generations, the mean response per generation in length at one year was 6.2% of the control mean, while the mean correlated response in weight was 21.5% of the control mean per generation. At the 4th generation, selected fish also appeared to be leaner than control fish when compared at the same size, and the response on weight was maximal (≈130% of the control mean) between 386 and 470 days post fertilisation. This high response is promising, however, the key points of the method have to be investigated in more detail.     

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.     

Acidophilic granular cells in the epidermis of the brown trout,Salmo trutta L.

Summary Acidophilic cells occur in the epidermis of several species of salmonid fish, although their abundance fluctuates considerably between individuals within the same population and at different times during the life cycle. The histology, histochemistry and ultrastructure of an acidophilic, granular celltype in the epidermis of the brown trout, Salmo trutta L., is described. At the light microscope level this cell type is easily distinguished from the large, mucus-secreting, epidermal goblet cells by its acidophilic, proteinaceous secretion. At the ultrastructural level this secretion consists of membrane-bound granules formed by the very active Golgi region. It is argued that the acidophilic, granular cell is not a transformed blood cell but constitutes a normal epidermal component of the brown trout. Possible roles of this cell in the function(s) of the epidermis are discussed.     

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     

Genetic structure of brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> L.) from the Hardangervidda mountain plateau (Norway) analyzed by microsatellite DNA: a basis for conservation guidelines

The Hardangervidda in southern Norway, the largest mountain plateau in Europe, has thousands of lakes and streams, mainly between 1000 and 1300 m above sea level, where brown trout is the only fish species. To describe the current genetic diversity of brown trout in this area, a total of 863 fish from 20 lakes were genotyped with eleven microsatellites. Most diversity is within lake populations, but diversity among geographical groups and populations within groups was significant, too. Neighbor-joining, principle coordinate analysis and Bayesian clustering show three major geographic groups in accordance with the river systems. Bias was caused by recent stocking in two lakes. Low/no genetic differentiation among some populations indicates that intermixing is common when lakes are well-connected, as was also shown by assignment test. We recommend preserving the genetic diversity of brown trout in this unique area by managing stocking in lake systems according to genetic structure.     

Microsatellite analyses of the trout of northwest Mexico)

The trout of northwest Mexico represent an undescribed group of fish considered part of the Oncorhynchus mykiss (Pacific trout) complex of species and subspecies. Recent genetic studies have shown these fish to have important genetic diversity and a unique evolutionary history when compared to coastal rainbow trout. Increased levels of allelic diversity have been found in this species at the southern extent of its range. In this study we describe the trout in the Sierra Madre Occidental from the rios Yaqui, Mayo, Casas Grandes and de Bavispe, and their relationship to the more southern distribution of Mexican golden trout (O. chrysogaster) using 11 microsatellite loci. Microsatellite allelic diversity in Mexican trout was high with a mean of 6.6 alleles/locus, average heterozygosity=0.35, and a mean F _st=0.43 for all loci combined. Microsatellite data were congruent with previously published mtDNA results showing unique panmictic population structure in the Rio Yaqui trout that differs from Pacific coastal trout and Mexican golden trout. These data also add support for the theory of headwaters transfer of trout across the Continental Divide from tributaries of the Rio de Bavispe into the Rio Casas Grandes. Rio Mayo trout share a close genetic relationship to trout in Rio Yaqui, but sample sizes from the Rio Mayo prevent significant comparisons in this study. Microsatellite analyses show significant allelic frequency differences between Rio Yaqui trout and O. chrysogaster in Sinaloa and Durango Mexico, adding further support for a unique evolutionary status for this group of northwestern Mexican trout.     

Dynamic micro-geographic and temporal genetic diversity in vertebrates: the case of lake-spawning populations of brown trout (Salmo trutta)

Conservation of species should be based on knowledge of effective population sizes and understanding of how breeding tactics and selection of recruitment habitats lead to genetic structuring. In the stream‐spawning and genetically diverse brown trout, spawning and rearing areas may be restricted source habitats. Spatio–temporal genetic variability patterns were studied in brown trout occupying three lakes characterized by restricted stream habitat but high recruitment levels. This suggested non‐typical lake‐spawning, potentially representing additional spatio–temporal genetic variation in continuous habitats. Three years of sampling documented presence of young‐of‐the‐year cohorts in littoral lake areas with groundwater inflow, confirming lake‐spawning trout in all three lakes. Nine microsatellite markers assayed across 901 young‐of‐the‐year individuals indicated overall substantial genetic differentiation in space and time. Nested gene diversity analyses revealed highly significant (≤P = 0.002) differentiation on all hierarchical levels, represented by regional lakes (F_LT = 0.281), stream vs. lake habitat within regional lakes (F_HL = 0.045), sample site within habitats (F_SH = 0.010), and cohorts within sample sites (F_CS = 0.016). Genetic structuring was, however, different among lakes. It was more pronounced in a natural lake, which exhibited temporally stable structuring both between two lake‐spawning populations and between lake‐ and stream spawners. Hence, it is demonstrated that lake‐spawning brown trout form genetically distinct populations and may significantly contribute to genetic diversity. In another lake, differentiation was substantial between stream‐ and lake‐spawning populations but not within habitat. In the third lake, there was less apparent spatial or temporal genetic structuring. Calculation of effective population sizes suggested small spawning populations in general, both within streams and lakes, and indicates that the presence of lake‐spawning populations tended to reduce genetic drift in the total (meta‐) population of the lake.