Genetic variation for tolerance to acidic water in salmonids

Water pH is an important factor affecting the general water quality as well as quality traits in fishes, and the magnitude of the effect varies among species. The massive and negative effect of acidification of rivers and lakes became evident during the 1960s and 1970s and caused the depletion of fish stocks in several countries in the northern hemisphere. Significant variation in tolerance to acidic water has been documented among salmonid species, and large genetic variation has been identified among strains of brown trout Salmo trutta, brook trout Salvelinus fontinalis and Atlantic salmon Salmo salar. For S. trutta, S. fontinalis and S. salar, there is considerable additive genetic variation in tolerance to acidic water, with heritabilities (h(2)) ranging from 0·09 to 0·27 for dead eyed-eggs (the period most sensitive to low pH). The main reasons for depletion of freshwater fish stocks are discussed.     

The influence of sex and spawning on levels of tryptophan, serotonin and 5-hydroxyindoleacetic acid in the brains of wild brook trout, Salvelinus fontinalis

Levels of tryptophan (TP), serotonin (5-hydroxytryptamine, 5HT) and 5-hydroxyindoleacetic acid (5HIAA) have been determined in the brains of wild brook trout, Salvelinus fontinalis (Mitchill), and brown trout, Salmo trutta L., using high performance liquid chromatography with electrochemical detection. Immediately prior to spawning, adult female brook trout exhibit higher levels of 5HT in the brain than adult males, immature brook trout and immature brown trout. After spawning, the highest levels of TP are found in spent males, which also have higher levels of 5HT in the brain than spent females and immature brook trout. Immature brook trout exhibit higher levels of 5HIAA than prespawning adults. This difference disappears after the spawning season. Serum protein levels and condition factors are lower in spent female brook trout; however, haematocrit values for both sexes remain unchanged after spawning.     

Stable isotope evidence of trophic interactions between introduced brook trout Salvelinus fontinalis and native brown trout Salmo trutta in a mountain stream of south-west France

The potential trophic impact of introduced brook trout Salvelinus fontinalis on native brown trout Salmo trutta in a mountain stream (south-west France) was investigated using stable isotope analysis (SIA). The isotopic signatures (δ¹³C and δ¹⁵N) of S. fontinalis were similar regardless of the absence or presence of S. trutta , and SIA mixing models revealed that S. fontinalis diet consisted mainly of terrestrial invertebrates. Conversely, a significant shift in S. trutta isotopic signatures (depletion of 1·6‰δ¹³C and enrichment of 0·6‰δ¹⁵N) was observed in sympatry with S. fontinalis ; this may be due to a dietary shift towards terrestrial invertebrates. Contrary to an expected dietary divergence in sympatry, an elevated level of dietary overlap was observed between the non-native and native salmonids when in co-occurrence. This dietary convergence is more likely to be due to behavioural interactions than to variations in food availability or fish displacements.     

Swimming performance of various freshwater Newfoundland salmonids relative to habitat selection and fishway design

Swimming ability of wild brook trout Salvelinus fontinalis , brown trout Salmo trutta , anadromous Atlantic salmon Salmo salar , and landlocked Atlantic salmon was examined using fixed and increasing velocity tests. Although brook trout and salmon parr were collected from the same site, brook trout were found generally in slow-moving pools whereas salmon were more common in faster riffle areas. Salmon parr could hold station indefinitely in currents in which brook trout could only maintain themselves briefly. Therefore, selection of fast-water areas by salmon parr may impose a velocity barrier to sympatric juvenile brook trout, reducing competition between the species. Performance comparisons also indicate that anadromous Atlantic salmon possess slightly greater sustained ability than landlocked salmon, possibly due to altered selective pressure associated with their different life histories. Finally, fishways and culverts in Newfoundland can now be designed using models generated from performance data collected from native salmonid species.     

Post-stocking movements and recapture of hatchery-reared trout released into flowing waters—a review

The success of stocking with hatchery-reared trout has been the subject of varied investigations for the past half-century. Percentage returns are summarised, and literature on the post-stocking movements of hatchery-reared trout is reviewed. Factors affecting the poststocking movements are considered, special attention being paid to studies on industrial rivers. Highest returns are obtained from stockings, with trout of a size suitable for angling, made during or shortly before the angling season. The majority of stocked brown trout, Salmo trutta tend to remain close to the area of stocking, but brook trout, Salvelinus fontinalis and rainbow trout, Salmo gairdneri show greater movement, usually in a down-stream direction. Greater dispersion of all species occurs if they have overwintered prior to capture or have been stocked in'cold water'or in small upstream stretches of river.     

Host specificity and geographical distribution of Eubothrium in European salmonid fish

The host specificity and distribution of Eubothrium crassum (Bloch, 1779) and Eubothrium salvelini (Schrank, 1790), morphologically fairly similar pseudophyllidean tapeworms parasitizing salmonid fish, were critically assessed on the basis of morphological and genetic evaluation of extensive material collected from different definitive hosts and geographical regions in Europe. Eubothrium crassum occurs in fish of the genera Salmo, i.e. salmon (S. salar - both freshwater and marine), sea trout (S. trutta trutta), brown trout (S. trutta fario), and lake trout (S. trutta lacustris), and also in Danubian salmon (Hucho hucho) and vendace (Coregonus albula). Eubothrium salvelini parasitizes Arctic char (Salvelinus alpinus) and brook trout (Salvelinus fontinalis) in Europe, and also whitefish (Coregonus wartmanni). Rainbow trout (Oncorhynchus mykiss), which is not a native European fish species, was found to be a suitable definitive host for both Eubothrium species, which may occur simultaneously in the same fish. Previous records of E. crassum in Arctic char and brook trout, and those of E. salvelini in fish of the genus Salmo were most probably misidentifications. Most studies of Eubothrium have involved salmonids from the northern part of Europe, with few records from southern and south-eastern Europe. This study also confirmed the reliability of the morphology of the apical disc for the discrimination of E. crassum and E. salvelini.     

Transmission of Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) to Fredericella sultana (Bryozoa: Phylactolaemata) by various fish species

Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonids and freshwater bryozoans, which causes proliferative kidney disease (PKD) in the fish host. To test which fish species are able to transmit T. bryosalmonae to bryozoans, an infection experiment was conducted with 5 PKD-sensitive fish species from different genera. Rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, brook trout Salvelinus fontinalis, grayling Thymallus thymallus and northern pike Esox lucius were cohabitated with T. bryosalmonae-infected Fredericella sultana colonies and then subsequently cohabitated with statoblast-reared parasite free Bryozoa. Statoblasts from infected colonies were tested by PCR to detect cryptic stages of T. bryosalmonae, which may indicate vertical transmission of the parasite. In this study, brown trout and brook trout were able to infect Bryozoa, while there was no evidence that rainbow trout and grayling were able to do so. Few interstitial kidney stages of the parasite were detected by immunohistochemistry in brown trout and brook trout, while rainbow trout and grayling showed marked proliferation of renal interstitial tissue and macrophages with numerous parasite cells. Intraluminal stages in the kidney tubules were only detected in brown trout and rainbow trout. In contrast to previous observations, pike was not susceptible to PKD in these trials according to the results of T. bryosalmonae-specific PCR. No DNA of T. bryosalmonae was detected in any statoblast.     

Fate of maternal mtDNA following 60Co inactivation of maternal nuclear DNA in unfertilized salmonid eggs.

The effects of gamma irradiation on nuclear DNA and mitochondrial DNA (mtDNA) were examined by exposing unfertilized salmonid eggs to a 60Co source. Brown trout (Salmo trutta) eggs exposed to 60Co were fertilized with sperm from brook trout (Salvelinus fontinalis), and brook trout eggs exposed to 60Co were fertilized with sperm from splake males (S. namaycush x S. fontinalis). In both types of matings only paternal allozymes were found in embryos, confirming the inactivation of the nuclear genome in the eggs. Analysis of mtDNA in these same embryos showed exclusively maternal mtDNA. The absence of paternal mtDNA among any of the embryos supports the predominance of maternal inheritance of mtDNA in vertebrates and suggests that mtDNAs are more resistant to cobalt inactivation than nuclear DNAs based on structure or numerical superiority to maternal nuclear DNA. Inactivation of maternal nuclear DNA, fertilization, and an induced return to the diploid state provide a means for producing an inbred organism having the nuclear genome of the paternal parent (androgenetic) and the mitochondrial genome of the female.     

Phylogeography,genetic structure,and conservation of the endangered Caspian brown trout, <Emphasis Type="Italic">Salmo trutta caspius</Emphasis> (Kessler, 1877), from Iran

The Caspian Sea, the largest inland closed water body in the world, has numerous endemic species. The Caspian brown trout (Salmo trutta caspius) is considered as endangered according to IUCN criteria. Information on phylogeography and genetic structure is crucial for appropriate management of genetic resources. In spite of the huge number of studies carried out in the Salmo trutta species complex across its distribution range, very few data are available on these issues for S. trutta within the Caspian Sea. Mitochondrial (mtDNA control region) and nuclear (major ribosomal DNA internal transcribed spacer 1, ITS-1, and ten microsatellite loci) molecular markers were used to study the phylogeography, genetic structure, and current captive breeding strategies for reinforcement of Caspian trout in North Iranian rivers. Our results confirmed the presence of Salmo trutta caspius in this region. Phylogenetic analysis demonstrated its membership to the brown trout Danubian (DA) lineage. Genetic diversity of Caspian brown trout in Iranian Rivers is comparable to the levels usually observed in sustainable anadromous European brown trout populations. Microsatellite data suggested two main clusters connected by gene flow among river basins likely by anadromous fish. No genetic differences were detected between the hatchery sample and the remaining wild populations. While the current hatchery program has not produced detectable genetic changes in the wild populations, conservation strategies prioritizing habitat improvement and recovering natural spawning areas for enhancing wild populations are emphasized.     

Brown trout Salmo trutta express different morphometrics due to divergence in the rearing environment

Variation in the body morphology of juvenile brown trout Salmo trutta was studied for both wild and hatchery-reared individuals from the same gene pool. The thin-plate spline (TPS) method by pointing landmarks was used to characterize juveniles from their natal environment, the River Kuusinkijoki in eastern Finland, and from wild parents raised in a hatchery environment. Differences were found in the morphometrics of juvenile S. trutta from the two different environments. Wild S. trutta are characterized by a longer head and shorter anterior part of the trunk compared to hatchery S. trutta. Stocked to their natal river with wild S. trutta, the hatchery fish became characterized with more similar morphometrics to their wild counterparts. The characteristics of the body form are explained by the differing environmental conditions in the wild and hatchery. It is concluded that a simple hatchery environment may delay the development of morphological characteristics important in a natural river environment.     

Failure of interspecies androgenesis in salmonids

Androgenetic development of salmonid embryos was induced in recipient oocytes from the same or other species (intra- or interspecies androgenesis). Parameters for induced androgenesis were investigated in brown trout Salmo trutta and brook trout Salvelinus fontinalis . Reciprocal androgenetic and control crosses were conducted among fishes from three genera: Oncorhynchus (rainbow trout, O. mykiss ), Salmo (brown trout) and Salvelinus (brook trout), and within two genera: Salmo (brown trout and Atlantic salmon, S. salar ) and Salvelinus (brook trout and Arctic charr, S. alpinus ). Live hatched androgenetic progenies were obtained in all intraspecies variants, where oocytes and sperm originated from the same species. Interspecies androgenesis resulted in no viable larvae, despite the fact that most hybrid controls and intraspecies androgenetic individuals were viable. When recipient oocytes originated from other genera (interspecific intergeneric androgenesis), embryonic development ceased in early developmental stages, except for haploid controls of brook trout produced in eggs of brown trout. Survival of embryos to the eyed-egg stage was relatively high in the intrageneric androgenesis experiment. Nevertheless, none of these embryos survived to hatching. Some of the presumed Atlantic salmon individuals developing in brown trout eggs contained maternal DNA, questioning the accuracy of enucleation using irradiation. The inability to induce interspecific androgenesis among the examined salmonid species may have been the result of substantial kariotypical and developmental differences between spermatozoal donors and oocyte recipients, causing an incompatibility between maternal cytoplasmic regulatory factors and the paternal nuclear genome.     

Daylight responses to overhead cover in stream channels for fry of four salmonid species

Brown trout ( Salmo trutta ), Atlantic salmon ( Salmo salar ), brook trout ( Salvelinus fontinalis ) and lake trout ( Salvelinus namaycush ) fry entering the free-feeding stage, were tested for overhead cover preferences in stream channels at different temperatures and water velocities. Atlantic salmon showed strong preferences for overhead cover, brown trout moderate preferences, whereas lake trout had preferences only at high temperatures, i.e. 12.4–19.2°C. Brook trout showed no cover preferences. Temperature influenced cover preferences of Atlantic salmon and brown trout considerably. The fry tended to seek more cover at low temperatures, i.e. 6.0–8.3°C     

An epizootic in chinook salmon (Oncorhynchus tshawytscha) caused by a sorbitol-positive serovar 2 strain of Yersinia ruckeri

Enteric redmouth disease is described in chinook salmon (Oncorhynchus tshawytscha) at a state hatchery in Sand Ridge, Illinois. Biochemical, isoenzyme, and serological data indicated that the epizootic was caused by a sorbitol-fermenting Serovar 2 strain of Yersinia ruckeri. In laboratory experiments the isolate was pathogenic for both brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar).     

Growth rate differences between resident native brook trout and non-native brown trout

Between species and across season variation in growth was examined by tagging and recapturing individual brook trout Salvelinus fontinalis and brown trout Salmo trutta across seasons in a small stream (West Brook, Massachusetts, U.S.A.). Detailed information on body size and growth are presented to (1) test whether the two species differed in growth within seasons and (2) characterize the seasonal growth patterns for two age classes of each species. Growth differed between species in nearly half of the season- and age-specific comparisons. When growth differed, non-native brown trout grew faster than native brook trout in all but one comparison. Moreover, species differences were most pronounced when overall growth was high during the spring and early summer. These growth differences resulted in size asymmetries that were sustained over the duration of the study. A literature survey also indicated that non-native salmonids typically grow faster than native salmonids when the two occur in sympatry. Taken together, these results suggest that differences in growth are not uncommon for coexisting native and non-native salmonids.     

The susceptibility of Salvelinus fontinalis (Mitchill) to Gyrodactylus salaris Malmberg (Platyhelminthes; Monogenea) under experimental conditions

The host specificity of Gyrodaclylus Solaris is examined experimentally with respect to its ability to infect the brook trout, Salvelinus fontinalis . The parasite readily attached to and reproduced on parr of this host and infections grew for c. 20 days from first monitoring (c. 30 days from first infection) before declining. Parasites could persist on this host for up to 70 days before finally disappearing. The pattern of infection resembled that seen in many other gyrodactylid species on their normal hosts, and suggested the action of a host response, In this respect infections of G. salaris on parr of S. fontinalis , anadromous Salvelinus alpinus, Oncorhynchus mykiss, Thymallus thymallus and Baltic Salmo salar follow a normal pattern, while infections of Norwegian S. salar are unusual in a continued unchecked growth, until the host dies, under pooled laboratory conditions.     

Brown trout Salmo trutta redd superimposition by spawning Lampetra species in a lowland stream

Reproductive interaction between sympatric lampreys and salmonids was studied. The superimposition of brown trout Salmo trutta redds by spring-spawning river lamprey Lampetra fluviatilis and brook lamprey Lampetra planeri was examined in a small lowland stream of western Lithuania. A high superimposition rate of S. trutta redds by both L. fluviatilis (up to 83%) and L. planeri (up to 48%) was found, when the spawning intensity of Lampetra spp. was high. The occurrence of this phenomenon is the result of the overlap in the spawning habitat preferences at the reach-scale and at the microhabitat scale for the three species. One of the main requirements for Lampetra spp. spawning site selection was the negative streambed slope, an essential trait of the pool-riffle transitional zone. The structure of the salmonid redd created a considerable negative microhabitat slope suitable for Lampetra spp. spawning, which put the redds under a higher susceptibility to be superimposed. The timing of Lampetra spp. spawning overlapped closely with the emergence of S. trutta fry, suggesting a probable ecological effect of superimposition on S. trutta in the pre-emergent and emerging stages.     

Experimental and natural host specificity of Loma salmonae (Microsporidia)

The microsporidian Loma salmonae (Putz, Hoffman & Dunbar, 1965) Morrison & Sprague, 1981 has caused significant gill disease in Pacific salmon Oncorhynchus spp. Host specificity of the parasite was examined experimentally by per os challenge of selected salmonids and non-salmonids with infective chinook salmon O. tshawytscha gill material. Pink Oncorhynchus gorbuscha and chum salmon O. keta, brown Salmo trutta and brook trout Salvelinus fontinalis, and chinook salmon (controls) were positive, whereas Atlantic salmon Salmo salar and Arctic char Salvelinus alpinus were negative. In addition, no non-salmonids were susceptible to experimental exposure. Wild Pacific salmon species in British Columbia, Canada, were examined for L. salmonae during their freshwater life history stages (smolts, prespawning, spawning). All stages were infected, although infections in smolts were only detectable using a L. salmonae-specific PCR test. Many previous Loma spp. described from Oncorhychus spp. are likely L. salmonae based on host, parasite morphology, and site of infection.     

Comparative analysis of intra-individual and inter-species DNA sequence variation in salmonid ribosomal DNA cistrons

This study examines sequence divergence in three spacer regions of the ribosomal DNA (rDNA) cistron, to test the hypothesis of unequal mutation rates. Portions of two transcribed spacers (ITS-1 and 5' ETS) and the non-transcribed spacer (NTS) or intergenic spacer (IGS) formed the basis of comparative analyses. Sequence divergence was measured both within an individual lake trout (Salvelinus namaycush) and among several related salmonid species (lake trout; brook trout, Salvelinus fontinalis; Arctic char, Salvelinus alpinus; Atlantic salmon, Salmo salar; and brown trout, Salmo trutta). Despite major differences in the length of the rDNA cistron within individual lake trout, minimal sequence difference was detected among cistrons. Interspecies comparisons found that molecular variation in the rDNA spacers did not conform to the predicted pattern of evolution (ITS spacers相似文献   

Isolation of a Loma salmonae variant: biological characteristics and host range

A Salvelinus -infecting variant of Loma salmonae , derived from naturally-infected Chinook salmon Oncorhynchus tshawytscha by serial passage through brook trout Salvelinus fontinalis , has been isolated and amplified. Loma salmonae SV ( Salvelinus -variant) has a high preference for species of Salvelinus (brook trout and Arctic charr S. alpinus ) and low virulence and preference for species of Oncorhynchus (rainbow trout O. mykiss , Chinook salmon, cohoSalmon O. kisutch ) or Salmo (Atlantic salmon Salmo salar ). Although this variant of L. salmonae was different from the original, the differences do not justify describing it as a new species, although definitive determination is pending.     

Abundance and distribution of Salmincola edwardsii (Copepoda) on anadromous brook trout, Salvelinus fontinalis, (Mitchill) in the Moisie River system, Quebec

Riviere a la Truite, a tributary of the Moisie River, is probably a focus of Salmincola edwardsii transmission within the system. Differences in prevalence of the copepod on fish between Riviére à la Truite and the main river suggested that up to 41% of anadromous brook trout, Salvelinus fontinalis , in the Moisie River system overwinter in the tributary. Infected fish were generally less than 200 mm long and copepods were attached almost exclusively to the fins and their bases. The primary site of copepod attachment at low intensities of infection was the adipose fin but at high intensities the dorsal fin was most frequently infected. This displacement in attachment location with increased intensity may result in density-dependent mortality of copepods. Copepods were overdispersed on the host population at each major sampling time and data fit a negative binomial distribution (k ranged from 0.2 to 0.8).