Joint Segregation of Biochemical Loci in Salmonidae. II. Linkage Associations from a Hybridized Salvelinus Genome (S. NAMAYCUSHxS. FONTINALIS)

The results of more than 300 pairwise examinations of biochemical loci for joint segregation in brook trout (Salvelinus fontinalis) and in the hybridized genome of lake trout (S. namaycush) x brook trout are summarized. Nineteen loci have been assigned to the following eight linkage groupings on the basis of nonrandom assortment, including cases of both classical linkage and pseudolinkage: ODH with PMI with PGI-3, PGI-2 with SDH, ADA-1 with AGP-2, AAT-(1,2) with AGP-1 with MDH-1, MDH-3 with MDH-4, LDH-3 with LDH-4, IDH-3 with ME-2 and GUS with CPK-1. Pseudolinkage (an excess of nonparental progeny types) was observed only for male testcross parents. The results suggest that this phenomenon involves homeologous chromosome arms as evidenced by the de novo association of presumed duplicate loci in each case. Classical linkage has not been found for the five pairs of duplicate loci examined in Salvelinus, suggesting that not all of the eight metacentrics in the haploid complement involve fusions of homeologous chromosomes. Females consistently showed a greater degree of recombination.     

Cytogenetic analysis of pseudolinkage of ldh Loci in the teleost genus salvelinus

Cytological and genetic analyses provide evidence that spontaneous centric fusion and fission can account for curious patterns of pseudolinkage of two LDH loci in males of brook trout (Salvelinus fontinalis) and in the F₁, F₂ and backcross generations of lake trout (S. namaycush) x brook trout hybrids. Intraindividual polymorphisms for acrocentric and metacentric chromosomes in somatic and gonadal tissue of these fish have been related to the proposed polyploid evolution in Salmonidae.     

Isolation and cross‐familial amplification of 41 microsatellites for the brook charr (Salvelinus fontinalis)

The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty‐seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis.     

Spatial patterns of hybridization between bull trout, <Emphasis Type="Italic">Salvelinus confluentus</Emphasis>, and brook trout, <Emphasis Type="Italic">Salvelinus fontinalis</Emphasis> in an Oregon stream network

Hybridization with introduced species represents a serious threat to the persistence of many native fish populations. Brook trout (Salvelinus fontinalis) have been introduced extensively throughout the native range of bull trout (S. confluentus) and hybridization has been documented in several systems where they co-exist and is seen as a significant threat to the persistence of bull trout populations. We identified a group of diagnostic microsatellite loci to differentiate bull trout and brook trout and then used these loci to examine the spatial distribution of hybrids in the Malheur River basin, Oregon USA. In random samples of approximately 100 fish from each of three creeks we identified 181 brook trout, 112 bull trout and 14 hybrids. Although bull trout, brook trout and hybrids were found in all three creeks, they were not evenly distributed; brook trout were primarily found in the lower sections of the creeks, bull trout further upstream, and hybrids in the areas of the greatest overlap. One creek with a population of brook trout in a headwater lake provided an exception to this pattern; brook trout were found distributed throughout the creek downstream of the lake. Several post-F1 hybrids were identified suggesting that hybrids are reproducing in the Malher River Basin. Mitochondrial DNA analysis indicated that both female bull trout and brook trout are involved in hybridization events. Analysis of population structure suggested that brook trout have established multiple spawning populations within the Malheur system. Data presented in this study suggest that relative abundance of brook trout and habitat quality are important factors to consider when evaluating the threat of hybridization to bull trout populations.     

Sex linkage in salmonids: Evidence from a hybridized genome of brook trout and arctic charr

In second-generation sparctics (Salvelinus fontinalis × Salvelinus alpinus) backcrossed toS. fontinalis, we have identified tight classical linkage of phenotypic sex withLdh-1, Aat-5, andGpi-3. We designate this locusSex-1 and suggest that it may be the primary sex-determining locus in salmonids. Cumulative salmonid gene-to-centromere map distances for the three biochemical loci put the order as centromere—Ldh-1—(Aat-5 andGpi-3), with the latter two loci being tightly linked. An absence of association of phenotypic sex (presumably Sex-1) with these same three loci and other loci known to be linked to these loci is shown in splakes (S. fontinalis × Salvelinus namaycush) and cutbows (Salmo gairdneri × Salmo clarki). These data imply that the linkage ofSex-1 with these loci is found only inS. alpinus and support the view thatSex-1 lies across the centromere from these three loci inS. alpinus, representing a Robertsonian fusion not found in any of the other four species. A similar specific Robertsonian fusion is argued forS. gairdneri, whereSex-1 may be linked across a centromere to another biochemical locus (Ha). These linkage results and chromosomal observations of other investigators suggest thatSex-1 lies on an information-depauperate arm.     

Characterization of 20 highly variable tetranucleotide microsatellite loci for bull trout (Salvelinus confluentus) and cross‐amplification in other Salvelinus species

We describe the isolation and development of 20 polymorphic tetranucleotide microsatellite loci for bull trout (Salvelinus confluentus). In a sample of 76 fish, we observed between four and 23 alleles per locus. These loci show greater levels of genetic diversity than other loci previously examined in bull trout. Seventeen of these loci were also polymorphic in at least one of the following species: Salvelinus alpinus, Salvelinus malma, Salvelinus namaycush and Salvelinus fontinalis. These loci will aid in our understanding of the molecular ecology of bull trout and other char.     

Hybridization between native white-spotted charr and nonnative brook trout in the upper Sorachi River,Hokkaido, Japan

Invasion status and impacts of nonnative brook trout (Salvelinus fontinalis) in a Hokkaido stream were investigated with field surveys and genetic analyses. Nonnative brook trout was detected in nine (41 %) of the 22 sampled reaches in three tributaries of the Sorachi River, Hokkaido, Japan. Based on the external pigmentation, twelve putative hybrids between brook trout and native white-spotted charr (Salvelinus leucomaenis) were collected in two reaches. Microsatellite and mitochondrial DNA data established that 58% of these hybrids were first-generation (F₁) progenies between male brook trout and female white-spotted charr. Our results suggest potential negative impacts of nonnative brook trout on native charr populations in Hokkaido through interspecific interactions.     

Joint segregation of biochemical loci in Salmonidae. III. Linkage associations in Salmonidae including data from rainbow trout (Salmo gairdneri)

The results of 107 pairwise examinations of joint segregation of biochemical and skin color loci in rainbow trout, Salmo gairdneri, are presented. Three examinations revealed significant nonrandom assortment: Idh-3 with Me-2, Ada-1 with G3p-3, and Mdh-3 with Mdh-4. We believe the first two instances to be cases of classical linkage and the latter instance to reflect pseudolinkage based on similar findings in Salvelinus. All known salmonid linkage associations are reviewed. The results of this summary indicate a high degree of genome conservatism among genera within the Salmonidae, which would seem to be in contrast to the highly plastic genome of this family based on karyotypic data. Data are presented which negate the view that Robertsonian fusion of homologous acrocentric chromosome arms was the preferred mode of metacentric formation in salmonid evolution.Much of this paper is based on a Ph.D. thesis by B. May (1980). Authorized for publication as Paper No. 6118 in the Journal Series of The Pennsylvania Agricultural Experiment Station, University Park, in cooperation with the Benner Spring Fish Research Station, The Pennsylvania Fish Commission, Bellefonte. This work was supported, in part, by NSF Grant DEB 7905838 to J. E. Wright and by NSF Doctoral Dissertation Research Grant DEB 7901674 to B. May.     

Non‐native trout limit native brook trout access to space and thermal refugia in a restored large‐river system

We used direct observation via snorkeling surveys to quantify microhabitat use by native brook (Salvelinus fontinalis) and non‐native brown (Salmo trutta) and rainbow (Onchorynchus mykiss) trout occupying natural and restored pool habitats within a large, high‐elevation Appalachian river, United States. Permutational multivariate analysis of variance (PERMANOVA) and subsequent two‐way analysis of variance (ANOVA) indicated a significant difference in microhabitat use by brook and non‐native trout within restored pools. We also detected a significant difference in microhabitat use by brook trout occupying pools in allopatry versus those occupying pools in sympatry with non‐native trout—a pattern that appears to be modulated by size. Smaller brook trout often occupied pools in the absence of non‐native species, where they used shallower and faster focal habitats. Larger brook trout occupied pools with, and utilized similar focal habitats (i.e. deeper, slower velocity) as, non‐native trout. Non‐native trout consistently occupied more thermally suitable microhabitats closer to cover as compared to brook trout, including the use of thermal refugia (i.e. ambient–focal temperature >2°C). These results suggest that non‐native trout influence brook trout use of restored habitats by: (1) displacing smaller brook trout from restored pools, and (2) displacing small and large brook trout from optimal microhabitats (cooler, deeper, and lower velocity). Consequently, benefits of habitat restoration in large rivers may only be fully realized by brook trout in the absence of non‐native species. Future research within this and other large river systems should characterize brook trout response to stream restoration following removal of non‐native species.     

Cytogenetic identification of genomic elements of brook trout (Salvelinus fontinalis) in the karyotype of Arctic char (Salvelinus alpinus) from the aquaculture broodstock

Growing interest of Arctic char (Salvelinus alpinus) aquaculture in Europe, and the fact that it can easily hybridize with brook trout (Salvelinus fontinalis) resulting in fertile progeny, led us to investigate fish from the farmed stocks. Chromosomes of sampled Arctic char were examined using conventional and molecular cytogenetic (FISH) techniques in order to determine possible contamination of genomic elements of brook trout. Investigated fish possessed karyotypes composed of 80–82 chromosomes and up to three chromosome fragments. Using staining methods and FISH approach enabled identification of the brook trout chromosomes in the eight out of twenty‐two examined Arctic char. Specific location of AT‐, GC‐ positive and NOR sites observed on chromosomes as well as chromosome fragments in the karyotypes of several individuals points on past chromosomal rearrangements in fish from examined broodstock. Based on our results, it may be assumed that individuals with the brook trout genomic elements, although phenotypically identified as Arctic chars, were hybrids. Our results highlights that special care should be taken to protect gene pools of brook trout and Arctic char in farms where both species are cultured.     

DEVELOPMENTAL INSTABILITY AND HIGH MERISTIC COUNTS IN INTERSPECIFIC HYBRIDS OF SALMONID FISHES

Interspecific hybrids have been proposed to have reduced developmental stability in comparison to their parental species because the parental genomes have not undergone selection for the maintenance of developmental stability when they occur together. We present data from four interspecific hybrids of salmonid fishes that support this view. Natural hybrids of bull trout (Salvelinus confluentus) with brook trout (Salvelinus fontinalis) and laboratory hybrids of rainbow trout (Salmo gairdneri) with Yellowstone (Salmo clarki bouvieri), westslope (S. c. lewisi), and coastal (S. c. clarki) cutthroat trout all have higher levels of fluctuating asymmetry than either of their parental species raised in the same environment. Thus, the hybrids have reduced developmental stability. The hybrids do not have meristic counts intermediate to the counts of the parental species. The hybrids usually have counts as high as the species with the higher count for those characters that differ between the parental species and often have higher counts for those characters that do not differ between the parental species. We suggest that the tendency for interspecific hybrids to have high meristic counts may be related to differences between the species in the length and timing of the developmental periods during which the counts of the characters are determined.     

Experimental sea ranching of brook trout, Salvelinus fontinalis Mitchill

An experiment to induce anadromy in a population of wild brook trout, Salvelinus fontinalis , was conducted near Sept-Iles, Quebec, in 1978–1979. Brook trout were captured from the Matamek River, tagged and transported to the Matamek River estuary during late spring and early summer, and allowed free movement between an impassable waterfall 0.7 km upstream and the sea. Fish were recaptured in autumn as they returned to fresh water. Over two years, 34.0% of the released fish were recaptured. Best returns were in the 2+ and 3+ age classes with 38.0 and 62.1% recaptured, respectively. Straying of transplanted fish appeared to be <1%. All age classes included sea run brook trout (sea trout) but the largest percentages of sea trout occurred in older fish. Growth was better in sea trout than in fish which did not develop anadromy, presumably a function of an increased food supply at sea. Severe tagging effects stunted growth and probably suppressed anadromy, especially among younger fish. Sexual characteristics of recaptured fish indicated suppressed maturation of gonads in sea trout compared to fish remaining in fresh water and there was a shift to a larger percentage of females in the sea trout. Comparisons between our results and data on other anadromous Salvelinus species underscore the potential for sea-ranching of trout and char as a moderate effort, high yield aquaculture technique.     

Effects of different protein and carbohydrate levels on growth performance and feed utilisation of brook trout,Salvelinus fontinalis (Mitchill, 1814), at two temperatures

A 12‐week feeding trial was conducted to determine the optimum dietary protein requirement of brook trout, Salvelinus fontinalis, at 15 and 19°C. Twelve iso‐energetic (22 MJ · kg^?1) and iso‐lipidic (23%) diets (36–58% protein at 2% increments) were prepared. Fish (29.45 ± 3.25 g · fish^?1) were fed 2% of body weight per day, divided into two equal rations. The specific growth rate (SGR, % · day^?1), feed efficiency ratio (FER), productive protein value (PPV), productive lipid value (PLV) and productive energy value (PEV), apparent digestibility of diet (AD_DM) and protein (AD_CP) were significantly higher at optimum temperature (15°C). Increasing PPV with increasing dietary carbohydrate and with decreasing dietary protein content was due to the protein‐sparing effect of carbohydrates. A piecewise regression (broken line) model between the SGR and digestible dietary protein level revealed that the digestible dietary protein requirement of brook trout was 44 and 40% at 15 and 19°C, respectively. When PPV (digestible protein retention basis) was modelled with a broken line, the digestible protein requirement of brook trout was 39 and 35% at 15 and 19°C, respectively. A reduction in dietary protein content balanced by increased gelatinised carbohydrate might be useful for improving the protein utilization efficiency for growth at 15 and 19°C; however, the growth and feed efficiency was lower at the elevated temperature.     

Comparing competitive ability and associated metabolic traits between a resident and migratory population of bull trout against a non-native species

Juvenile bull trout Salvelinus confluentus from two geographically and ecologically distinct populations were compared with regard to their ability to compete with non-native brook trout Salvelinus fontinalis in an artificial stream, and with respect to their rates of oxygen consumption. Bull trout collected from a migratory population foraged more successfully against brook trout competitors than those from a resident population, capturing more of a limited amount of food items presented. The migratory population was also more aggressive (measured by the number of nips, chases and lateral threat displays) against brook trout competitors than the resident population. Bull trout from the migratory population had a higher oxygen consumption rate (203 mg O₂ kg · hr^-1) in the field than similar sized fish from the resident population (183 mg O₂ kg · hr^-1). These results suggest native bull trout have population-level variation in competitive ability against a non-native species and such competitive ability is positively associated with metabolism and migratory life history.     

Allozyme Polymorphisms and Biochemical-Genetic Taxon Markers in Lampreys (Lampetra, Eudontomyzon, Petromyzon)

Variation at 23 putative enzyme-coding loci was scored in 424 lampreys, including 321 European brook lampreys (Lampetra planeri), 83 European river lampreys (L. fluviatilis), 11 Ukrainian brook lampreys (Eudontomyzon mariae), and nine sea lampreys (Petromyzon marinus). Twelve polymorphisms are described for Lampetra species (LDH*, SOD-2*, PNP*, AAT-1*, AK-1*, ES-2*, LGL*, MPI*, GPI-1*, GPI-2*, PGM*, IDHP-2*), and two each for E. mariae (GPI-1*, ME-2*) and P. marinus (MDH-1*, ME-2*). Diagnostic allozymes are presented for the discrimination of lamprey taxa, some of which are difficult to recognize from the morphology of ammocoetes larvae, the life stage usually encountered when collecting cyclostomes. The allelic markers described permit the clear allocation to a genus, except for the species L. fluviatilis and L. planeri, which are not differentiated by qualitative allozyme analysis.     

Diel foraging in relation to available prey in an Adirondack Mountain stream fish community

The diets of the fish community of Trucka Brook, a small stream located in the central Adirondack Mountains in northern New York, were examined in relation to the bottom fauna and invertebrate drift. Measures of overlap were calculated between the diets of each fish species examined, brook trout (Salvelinus fontinalis), blacknose dace (Rhinichthys atratulus), creek chub (Semotilus atromaculatus) and pearl dace (Semotilus margarita). Overlap was also examined between the fish diets and bottom and drift samples. Blacknose dace, pearl dace and brook trout had the most similar diets which were closely associated with the benthos. Creek chub had the most distinctive diets which did not compare well with any other fish species during either diurnal or nocturnal periods. The mayfly nymph Litobranchia recurvata was the most abundant bottom invertebrate and was the major prey of benthic feeding fishes. The invertebrate drift did not compare favorably with any of the fishes' diets because of the predominance of large cased limnephilid larvae (primarily Psychoglypha sp.) which were not readily consumed by fish.     

Species-specific probe,based on 18S rDNA sequence,could be used for identification of the mucilage producer microalga <Emphasis Type="Italic">Gonyaulax fragilis</Emphasis> (Dinophyta)

Brook trout (Salvelinus fontinalis) in Appalachia experience prolonged periods of poor feeding conditions, particularly during summer and fall. To determine which prey organisms are important in sustaining brook trout populations, we monitored the feeding patterns of a population of brook trout over the course of 2 years with an emphasis on seasonal change. We employed a bioenergetics model to estimate whether or not each fish had obtained enough energy to meet daily metabolic demand. As a result, qualitative comparisons between fish feeding above maintenance ration (successfully feeding fish) and fish feeding below maintenance ration (unsuccessfully feeding fish) were possible. With the exception of winter, brook trout derived significantly more energy from terrestrial organisms than aquatic organisms. During each season, successfully feeding brook trout fed on greater proportions of specific prey types. Terrestrial Coleoptera and Lepidoptera consistently proved to be important prey during warmer seasons, while large organisms such as vertebrates and crayfish appeared to be important during winter. Our findings suggest that terrestrial organisms are more important than aquatic organisms in sustaining brook trout populations. Further, certain large and abundant terrestrial taxa are critical in providing energy to brook trout.     

Can replacement of native by non‐native trout alter stream‐riparian food webs?

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Brown trout and food web interactions in a Minnesota stream

1. We examined indirect, community‐level interactions in a stream that contained non‐native brown trout (Salmo trutta Linnaeus), native brook trout (Salvelinus fontinalis Mitchill) and native slimy sculpin (Cottus cognatus Richardson). Our objectives were to examine benthic invertebrate composition and prey selection of fishes (measured by total invertebrate dry mass, dry mass of individual invertebrate taxa and relative proportion of invertebrate taxa in the benthos and diet) among treatments (no fish, juvenile brook trout alone, juvenile brown trout alone, sculpin with brook trout and sculpin with brown trout). 2. We assigned treatments to 1 m² enclosures/exclosures placed in riffles in Valley Creek, Minnesota, and conducted six experimental trials. We used three designs of fish densities (addition of trout to a constant number of sculpin with unequal numbers of trout and sculpin; addition of trout to a constant number of sculpin with equal numbers of trout and sculpin; and replacement of half the sculpin with an equal number of trout) to investigate the relative strength of interspecific versus intraspecific interactions. 3. Presence of fish (all three species, alone or in combined‐species treatments) was not associated with changes in total dry mass of benthic invertebrates or shifts in relative abundance of benthic invertebrate taxa, regardless of fish density design. 4. Brook trout and sculpin diets did not change when each species was alone compared with treatments of both species together. Likewise, we did not find evidence for shifts in brown trout or sculpin diets when each species was alone or together. 5. We suggest that native brook trout and non‐native brown trout fill similar niches in Valley Creek. We did not find evidence that either species had an effect on stream communities, potentially due to high invertebrate productivity in Valley Creek.     

Heterochromatins and band karyotypes in three species of salmonids

Summary The heterochromatins of rainbow trout (Salmo gairdneri R.), brown trout (Salmo trutta fario L.) and brook trout (Salvelinus fontinalis M.) were characterized by sequential chromomycin A₃/distamycin A/DAPI (CDD) and DAPI/actinomycin D (DAPI/AmD) fluorescence. On most biarmed chromosomes, an equilocal localization of prominent DAPI/AmD positive, chromomycin A₃ negative, AT-rich blocks at the centromeres were observed in all three species. Band karyotypes of the three species were established. In rainbow trout, several DAPI/AmD positive heterochromatin blocks behaved positive in a silver-staining method. Mitotic and interphase studies proved the presence of inter-individual NOR variation in brown trout. The NORs of brook trout were localized on chromosomes 5, 10, 14, 15 and 29.