Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) differ in their suitability as hosts for the endangered freshwater pearl mussel (Margaritifera margaritifera) in northern Fennoscandian rivers

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Seventy‐five EST‐linked Atlantic salmon (Salmo salar L.) microsatellite markers and their cross‐amplification in five salmonid species

An Atlantic salmon (Salmo salar L.) expressed sequence tag (EST) database consisting of 58 146 ESTs was screened for microsatellite sequences. Subsequent development of 75 polymorphic EST‐associated microsatellite markers in this species is described together with cross‐species amplification results of 133 gene‐associated tandem repeat markers in five salmonid species (Salmo trutta, Oncorhynchus mykiss, Salvelinus aplinus, Thymallus thymallus, Coregonus lavaretus). The number of alleles among EST‐linked microsatellites in Atlantic salmon ranged from two to 41 with an average of 12 alleles per locus. Cross‐species amplification resulted in detection of a total of 111 polymorphic locus‐species combinations (12–32 loci per species).     

Evidence for an autumn downstream migration of Atlantic salmon Salmo salar (Linnaeus) and brown trout Salmo trutta (Linnaeus) parr to the Baltic Sea

In the eastern Baltic rivers, anadromous salmonid parr are known to smoltify and migrate to the sea from March until June, depending on latitude, climate and hydrological conditions. In this study, we present the first records of autumn descent of brown trout Salmo trutta and Atlantic salmon Salmo salar from the Baltic Sea Basin. Otolith microchemistry analyses revealed that these individuals hatched in freshwater and had migrated to the brackish water shortly prior to capture. The fish were collected in 2006, 2008, 2009 and 2013 from Eru Bay (surface salinity 4.5–6.5 ‰), Gulf of Finland. This relatively wide temporal range of observations indicates that the autumn descent of anadromous salmonids is not a random event. These results imply that autumn descent needs more consideration in the context of the effective stock management, assessment and restoration of Baltic salmonid populations and their habitats.     

Characterization of the porcine transferrin gene (TF ) and its association with disease severity following an experimental Actinobacillus pleuropneumoniae infection

Transferrin (TF)‐mediated provision of iron is essential for a productive infection by many bacterial pathogens, and iron‐depletion of TF is a first line defence against bacterial infections. Therefore, the transferrin (TF) gene can be considered a candidate gene for disease resistance. We obtained the complete DNA sequence of the porcine TF gene, which spans 40 kb and contains 17 exons. We identified polymorphisms on a panel of 10 different pig breeds. Comparative intra‐ and interbreed sequence analysis revealed 62 polymorphisms in the TF gene including one microsatellite. Ten polymorphisms were located in the coding sequence of the TF gene. Four SNPs (c.902A>T, c.980G>A, c.1417A>G, c.1810A>C) were predicted to cause amino acid exchanges (p.Lys301Ile, p.Arg327Lys, p.Lys473Glu, p.Asn604His). We performed association analyses using six selected TF markers and 116 pigs experimentally infected with Actinobacillus pleuropneumoniae serotype 7. The analysis showed breed‐specific TF allele frequencies. In German Landrace, we found evidence for a possible association of the severity of A. pleuropneumoniae infection with TF genotypes.     

Feeding by Arizona trout (Salmo apache) and brown trout (Salmo trutta) at different light intensities

Synopsis Brown trout (Salmo trutta) were more efficient than Arizona trout (Salmo apache) in eating brine shrimp at starlight (10^–4 fL) light levels. Arizona trout required light levels moonlight (10^–3 fL) to feed. In bright light (50 fL), brown trout utilized cover to a much greater extent in both field and laboratory. Our study indicates that factors other than competition for food or habitat are probably causing the displacement of Arizona trout by brown trout when browns are stocked into the native habitat of Arizona trout.     

Evolution of Hox Clusters in Salmonidae: A Comparative Analysis Between Atlantic Salmon (Salmo salar) and Rainbow Trout (Oncorhynchus mykiss)

We studied the genomic organization of Hox genes in Atlantic salmon (Salmo salar) and made comparisons to that in rainbow trout (Oncorhynchus mykiss), another member of the family Salmonidae. We used these two species to test the hypothesis that the Hox genes would provide evidence for a fourth round of duplication (4R) of this gene family given the recent polyploid ancestry of the salmonid fish. Thirteen putative Hox clusters were identified and 10 of these complexes were localized to the current Atlantic salmon genetic map. Syntenic regions with the rainbow trout linkage map were detected and further homologies and homeologies are suggested. We propose that the common ancestor of Atlantic salmon and rainbow trout possessed at least 14 clusters of Hox genes, and additional clusters cannot be ruled out. Salmonid Hox cluster complements seem to be more similar to those of zebrafish (Danio rerio) than medaka (Oryzias latipes) or pufferfish (Sphoeroides nephelus and Takifugu rubripes), as both Atlantic salmon and rainbow trout have retained HoxCb ortholog, which has been lost in medaka and pufferfish but not in zebrafish. However, our data suggest that phylogenetically, the homologous genes within each cluster express mosaic relationships among the teleosts tested and, thus, leave unresolved the interfamilial relationships among these taxa. Sequence data from this article have been deposited within the EMBL/GenBank Data Libraries under the following accession numbers: AY677341, AY677342, AY677343, AY677344, AY677345, AY677346, AY677347, AY677348, AY677349, AY677350, AY677351, AY677352, AY677353, AY677354, AY677355, AY677356, AY677357, AY677358, AY677359, AY677360, AY677361, AY677362, AY677363, AY677364 and AY677365. [Reviewing Editor: Dr. Axel Meyer]     

Nucleolar DNA in oocytes of Salmo irideus (Gibbons)

The amplification of ribosomal genes has been studied in oocytes from Salmo irideus. In situ nucleic acid hybridization showed that the synthesis of nucleolar DNA begins in oogonium and proceeds slowly through leptotene and zygotene when a small amount of extrachromosomal nucleolar DNA is produced. In early pachytene there is a rapid build-up of nucleolar DNA demonstrable by rapid incorporation of tritiated thymidine. Synthesis stops completely in early diplotene when nucleolar DNA becomes dispersed over the inner surface of the nuclear envelope in the form of small Feulgen-positive granules. Photometric measurements of Feulgen stained nuclei showed that the final amount of amplified nucleolar DNA synthesized in each oocyte is approximately 20 g. The amplified DNA does not form a heterochromatic mass. The buoyant density of the amplified nucleolar DNA calculated from analytical centrifuge tracings in relation to DNA from Micrococcus luteus ( = 1.731 g cm^–3) is 1.715 g cm^–3 and corresponds to a G + C content of 57%. There are indications that the buoyant density of the somatic nucleolar DNA is lower than that of amplified nucleolar DNA.Similarities and differences between ribosomal gene amplifications in oocytes of Salmo irideus and the corresponding process in Xenopus are discussed.     

Identification of the sex chromosomes of brown trout (Salmo trutta) and their comparison with the corresponding chromosomes in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss)

Males are the heterogametic sex in salmonid fishes. In brown trout (Salmo trutta) the sex-determining locus, SEX, has been mapped to the end of linkage group BT-28, which corresponds to linkage group AS-8 and chromosome SSA15 in Atlantic salmon (Salmo salar). We set out to identify the sex chromosomes in brown trout. We isolated Atlantic salmon BAC clones containing microsatellite markers that are on BT-28 and also on AS-8, and used these BACs as probes for fluorescent in situ hybridization (FISH) analysis. SEX is located on the short arm of a small subtelocentric/acrocentric chromosome in brown trout, which is consistent with linkage analysis. The acrocentric chromosome SSA15 in Atlantic salmon appears to have arisen by a centric fusion of 2 small acrocentric chromosomes in the common ancestor of Salmo sp. We speculate that the fusion process that produced Atlantic salmon chromosome SSA15 disrupted the ancestral sex-determining locus in the Atlantic salmon lineage, providing the impetus either for the relocation of SEX or selection pressure for a novel sex-determining gene to arise in this species. Thus, the sex-determining genes may differ in Atlantic salmon and brown trout.     

Chromosome relationships in the genus Salmo

Chromosome numbers and polymorphisms in rainbow trout, Atlantic salmon, and brown trout are described. The karyotypes of these three species are compared with each other and with those of other salmonid fish from the genera Salmo, Salvelinus, and Oncorhynchus. Karyotype evolution from a postulated ancestral tetraploid is discussed.     

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.     

Genomic organization and characterization of two vomeronasal 1 receptor-like genes (ora1 and ora2) in Atlantic salmon Salmo salar

Olfactory receptors are encoded by three large multigene superfamilies (OR, V1R and V2R) in mammals. Fish do not possess a vomeronasal system; therefore, it has been proposed that their V1R-like genes be classified as olfactory receptors related to class A G protein-coupled receptors (ora). Unlike mammalian genomes, which contain more than a hundred V1R genes, the five species of teleost fish that have been investigated to date appear to have six ora genes (ora1-6) except for pufferfish that have lost ora1. The common ancestor of salmonid fishes is purported to have undergone a whole genome duplication. As salmonids have a life history that requires the use of olfactory cues to navigate back to their natal habitats to spawn, we set out to determine if ora1 or ora2 is duplicated in a representative species, Atlantic salmon (Salmo salar). We used an oligonucleotide probe designed from a conserved sequence of several teleost ora2 genes to screen an Atlantic salmon BAC library (CHORI-214). Hybridization-positive BACs belonged to a single fingerprint contig of the Atlantic salmon physical map. All were also positive for ora2 by PCR. One of these BACs was chosen for further study, and shotgun sequencing of this BAC identified two V1R-like genes, ora1 and ora2, that are in a head-to-head conformation as is seen in some other teleosts. The gene products, ora1 and ora2, are highly conserved among teleosts. We only found evidence for a single ora1-2 locus in the Atlantic salmon genome, which was mapped to linkage group 6. Fluorescent in situ hybridization (FISH) analysis placed ora1-2 on chromosome 12. Conserved synteny was found surrounding the ora1 and ora2 genes in Atlantic salmon, medaka and three-spined stickleback, but not zebrafish.     

Thiamin dynamics during the adult life cycle of Atlantic salmon (Salmo salar)

Thiamin is an essential water-soluble B vitamin known for its wide range of metabolic functions and antioxidant properties. Over the past decades, reproductive failures induced by thiamin deficiency have been observed in several salmonid species worldwide, but it is unclear why this micronutrient deficiency arises. Few studies have compared thiamin concentrations in systems of salmonid populations with or without documented thiamin deficiency. Moreover, it is not well known whether and how thiamin concentration changes during the marine feeding phase and the spawning migration. Therefore, samples of Atlantic salmon (Salmo salar) were collected when actively feeding in the open Baltic Sea, after the sea migration to natal rivers, after river migration, and during the spawning period. To compare populations of Baltic salmon with systems without documented thiamin deficiency, a population of landlocked salmon located in Lake Vänern (Sweden) was sampled as well as salmon from Norwegian rivers draining into the North Atlantic Ocean. Results showed the highest mean thiamin concentrations in Lake Vänern salmon, followed by North Atlantic, and the lowest in Baltic populations. Therefore, salmon in the Baltic Sea seem to be consistently more constrained by thiamin than those in other systems. Condition factor and body length had little to no effect on thiamin concentrations in all systems, suggesting that there is no relation between the body condition of salmon and thiamin deficiency. In our large spatiotemporal comparison of salmon populations, thiamin concentrations declined toward spawning in all studied systems, suggesting that the reduction in thiamin concentration arises as a natural consequence of starvation rather than to be related to thiamin deficiency in the system. These results suggest that factors affecting accumulation during the marine feeding phase are key for understanding the thiamin deficiency in salmonids.     

The Russian Gene Pool: Gene Geography of Serum Gene Markers (HP,GC,PI,and TF)

The study continues the series of works on the Russian gene pool. Gene geographic analysis of four serum gene markers best studied in the Russian population (HP, GC, PI, and TF) has been performed. Gene-geographic electronic maps have been constructed for 14 alleles of these loci and their correlations with geographic latitude and longitude. For all maps, statistical characteristics are presented, including the variation range and mean gene frequencies, partial and multiple correlations with latitude and longitude, and parameters of heterozygosity and interpopulation diversity. The maps of five alleles (HP*1, GC*2, GC*1S, PI*M2, and TF*C2) are shown and analyzed in detail. The genetic relief and structural elements of the maps are compared with the ecumenical trends, main variation patterns of these genes in northern Eurasia, and genetic characteristics of the indigenous populations of the Urals and Europe.     

Phenotypic differentiation analysis: A case study in hybridizing Çoruh trout (Salmo coruhensis), Rize trout (Salmo rizeensis) and brown trout (Salmo trutta fario)

The aim of this study was to determine and compare the phenotypic variation in Çoruh trout (Salmo coruhensis), Rize trout (Salmo rizeensis), brown trout (Salmo trutta fario) and their native hybrids (S. rizeensis × S. t. fario; S. t. fario × S. coruhensis; S. rizeensis × S. coruhensis). The numbers and diameters of red and black spots were determined on operculum, fins and above and below the lateral line. The results from this study indicate that there were differences in spotting pattern, colour pattern or fin pigmentation traits between S. rizeensis, S. t. fario, S. coruhensis and their hybrids. Consequently, native S. rizeensis, S. t. fario and S. coruhensis were affected by interaction and phenotypic plastic aspects of traits in S. rizeensis were dominant in their hybrids (S. rizeensis × S. t. fario; S. rizeensis × S. coruhensis).     

Genome‐wide methylation study of diploid and triploid brown trout (Salmo trutta L.)

The induction of triploidization in fish is a very common practice in aquaculture. Although triploidization has been applied successfully in many salmonid species, little is known about the epigenetic mechanisms implicated in the maintenance of the normal functions of the new polyploid genome. By means of methylation‐sensitive amplified polymorphism (MSAP) techniques, genome‐wide methylation changes associated with triploidization were assessed in DNA samples obtained from diploid and triploid siblings of brown trout (Salmo trutta). Simple comparative body measurements showed that the triploid trout used in the study were statistically bigger, however, not heavier than their diploid counterparts. The statistical analysis of the MSAP data showed no significant differences between diploid and triploid brown trout in respect to brain, gill, heart, liver, kidney or muscle samples. Nonetheless, local analysis pointed to the possibility of differences in connection with concrete loci. This is the first study that has investigated DNA methylation alterations associated with triploidization in brown trout. Our results set the basis for new studies to be undertaken and provide a new approach concerning triploidization effects of the salmonid genome while also contributing to the better understanding of the genome‐wide methylation processes.     

Fish Infected with Sphaerospora spp. Thélohan (Myxosporea) from Waters Enzootic for Proliferative Kidney Disease of Salmonids1

ABSTRACT. Sphaerospores were found among three species of fish examined from waters known to be enzootic for proliferative kidney disease (PKD) of salmonids. They were detected in the renal tubules of both hatchery-reared rainbow trout (Salmo gairdneri) exposed to the infectious stage of PKD and in chubs (Gila bicolor) in the headwaters of a hatchery where PKD is enzootic. Sticklebacks (Gasterosteus aculeatus) collected near net pens where Pacific salmon had experienced a PKD epizootic were also found to harbor sphaerospores in the lumen of the kidney tubules. The latter two host species contained developmental stages of a myxosporidan in the blood and in the lumen of the kidney tubules which are similar to those of PKX, the causative agent of PKD in salmonid fish. The sphaerospores observed in the rainbow trout are the first to be observed in this species. The similarity to previously observed developmental stages, rarity, and presence of these sphaerospores in salmonid fish from a hatchery where PKD is enzootic suggest that they are the most mature stage of the PKX myxosporidan yet observed.     

Early development of the chondrocranium in Salmo letnica(Karaman, 1924)(Teleostei: Salmonidae)

The ontogenetic development of the chondrocranium of Ohrid trout Salmo letnica was studied from hatching until 92 days post‐hatching (dph). Most of the samples were in toto trypsin cleared and stained, some specimens were used for serial histological sectioning. The serial histological sections of fish specimens at the age of 92 dph were used for a graphical reconstruction of the cartilaginous neurocranium. A chronological evaluation of the formation of the cartilaginous skull in the early development of S. letnica was performed. In order to investigate to what degree the ontogeny of the Ohrid trout is unique, the results were compared with data of the development of other salmonids, as well as some non‐salmonid teleosts. The development of the cartilaginous structures of the Ohrid trout was found to be similar to that of other salmonids. Most of the cartilage structures of the neurocranium and the viscerocranium are present at the moment of hatching of this species. A fully developed chondrocranium was observed at the age of 92 dph, when the first signs of cartilage resorption could also be observed.     

Overlooked aspects of the Salmo salar and Salmo trutta lifecycles

Reviews in Fish Biology and Fisheries - The salmonid lifecycle has been studied for over a 100 years. Our literature search indicated that the Atlantic salmon (Salmo salar) and brown trout...     

Characterization of Novel Minisatellite Repeat Loci in Atlantic Salmon (Salmo salar) and Their Phylogenetic Distribution

We present here the sequence and characterization of various minisatellite-like tandem repeat loci isolated from the genome of Atlantic salmon (Salmo salar). Their diversity of sequence and lack of core motifs common to minisatellites of other species suggest the presence of numerous and previously unidentified simple sequence repeat families in this salmonid. Evidence for their ubiquity was provided by screening of a salmon genomic library. Southern blot analysis of the phylogenetic distribution of a subset of the minisatellites found one sequence to be pervasive among vertebrates, others present only in Salmoninae or Salmonidae species, and one amplified only in Atlantic salmon. There is evidence for the positioning of microsatellite and minisatellite arrays in close proximity at many loci. Furthermore, one tandem repeat appears to have been inserted into the transposase coding region of a copy of the Tc1 transposon-like element recently identified in salmonids. Received: 9 October 1996 / Accepted: 20 May 1997