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.     

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.     

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.     

Natural replacement of invasive brown trout by brook charr in an upper Midwestern United States stream

Hydrobiologia - Competition with invasive species and a warming climate have threatened brook charr (Salvelinus fontinalis) populations throughout their native range. In particular, brown trout...     

Annual variability in the life-history characteristics of brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) in a subalpine Norwegian lake

The annual variability in growth and life history traits of brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.)) in Lake Atnsjøen, a Norwegian subalpine lake, was studied over a period of 13 years (1985–1997). The extent to which life-history characteristics recorded on one occasion can be regarded as representative for the population was explored. We found inter-cohort variation in growth for both species; estimates of asymptotic length (L _∞) in ten cohorts ranged between 225–305 mm (CV = 10.5%) for brown trout and 273–301 mm (CV = 4.1%) for Arctic charr. However, this variation was much lower than inter-population variation for brown trout based on single samples from 169 populations (CV = 24.6%). In Lake Atnsjøen, annual growth increment correlated highly with the number of days warmer than 7?°C (R ²=0.60–0.89) for brown trout, and days warmer than 10?°C (R ²=0.40–0.58) for Arctic charr. Females of Arctic charr were younger at sexual maturity than males, while no such difference was found in brown trout. Generally speaking, early maturing individuals of both species grew faster, particularly from age-2 and onwards, than immature individuals. Early maturing individuals, however, were smaller at maturity than those maturing one year older. Age and size at maturity were significantly correlated with asymptotic lengths only in Arctic charr females.     

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.     

Food borne parasites as indicators of trophic segregation between Arctic charr and brown trout

The habitat and diet choice and the infection (prevalence and abundance) of trophically transmitted parasites were compared in Arctic charr and brown trout living sympatrically in two lakes in northern Norway. Arctic charr were found in all main lake habitats, whereas the brown trout were almost exclusively found in the littoral zone. In both lakes the parasite fauna reflected the niche segregation between trout and charr. Surface insects were most common in the diet of trout, but transmit few parasites, and accordingly the brown trout had a relatively low diversity and abundance of parasites. Parasites transmitted by benthic prey such as Gammarus and insect larva, were common in both salmonid host species. Copepod transmitted parasites were much more common in Arctic charr, as brown trout did not include zooplankton in their diets. Parasite species that may use small fish as transport hosts, were far more abundant in piscivorous fish, especially brown trout. The seasonal dynamics in parasite infection were also consistent with the developments in the diet throughout the year. The study demonstrates that the structure of parasite communities of charr and the trout is highly dependent on shifts in habitat and diet of their hosts both on an annual base and through the ontogeny, in addition to the observed niche segregation between the two salmonid species.     

The effects of introduced salmonids on two native stream‐dwelling salmonids through interspecific competition

Using an artificial stream, habitat use by two sympatric native salmonids in the presence and absence of introduced salmonid species was investigated experimentally. When only native white‐spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou were sympatric, they occupied different microhabitats. In the presence of introduced brown trout Salmo trutta or rainbow trout Oncorhynchus mykiss , however, white‐spotted charr and masu salmon were observed to use a similar habitat and interspecific competition between white‐spotted charr and masu salmon was initiated. The study suggested that the coexistence of native salmonids was negatively affected through interspecific competition between native and introduced salmonids.     

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.     

The effects of fisheries management on harvest rates of native and non-native salmonid fish species

In central Europe, both brown trout Salmo trutta and European grayling Thymallus thymallus are threatened native salmonid species with high value in recreational angling and nature conservation. On the other hand, rainbow trout Oncorhynchus mykiss and brook trout Salvelinus fontinalis are intensively stocked non-native species of high angling value but no value for nature conservation. This study tested if harvest rates of native salmonids are negatively correlated to intensive stocking and harvest rates of non-native salmonids in inland freshwater recreational fisheries. Data were collected from 250 fishing sites (river and stream stretches) over 13 years using mandatory angling logbooks. Logbooks were collected from individual anglers by the Czech Fishing Union in the regions of Prague and Central Bohemia, Czechia (central Europe) and processed by the author of this study. In result, anglers harvested 200,000 salmonids with total weight of 80 tons over 13 years. Intensive stocking of multiple salmonid species lead to slightly lower harvests of native salmonids. Inversely, intensive harvests of multiple salmonid species lead to slightly higher harvest of native salmonids. Recapture rates of stocked salmonids were relatively low (0.6%–3.7%), proving fish stocking moderately ineffective. Since the effects of non-native salmonid stocking and harvest rates on native salmonid harvest were significant but not strong, it is suggested that rivers and streams that support fishing for non-native salmonids still support fishing for native salmonids. However, this idea does not apply for fishing sites with really high intensity of non-native salmonid stocking – harvest rates of natives were very low on these fishing sites.     

Piscivory by brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) in Norwegian lakes

Size and frequency of occurrence of prey of brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) were recorded in 13 Norwegian lakes during 1973–1990. Piscivores usually comprised less than 5% of the total population. Arctic charr were less piscivorous than brown trout. Trout and charr became piscivorous at 13 and 16 cm length, respectively. These size thresholds were similar to those of other facultative piscivorous freshwater fish species. When present, three-spined sticklebacks, Gasterosteus aculeatus (L.), were preferred by all length groups of piscivorous brown trout and Arctic charr. Length of prey increased with increasing predator length, and the mean body length of prey was about 33 and 25% of predator length for trout and charr, respectively. Yearlings of charr were not recorded as prey.     

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.     

Genetic architecture of body weight,condition factor and age of sexual maturation in Icelandic Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>)

The high commercial value from the aquaculture of salmonid fishes has prompted many studies into the genetic architecture of complex traits and the need to identify genomic regions that have repeatable associations with trait variation both within and among species. We searched for quantitative trait loci (QTL) for body weight (BW), condition factor (CF) and age of sexual maturation (MAT) in families of Arctic charr (Salvelinus alpinus) from an Icelandic breeding program. QTL with genome-wide significance were detected for each trait on multiple Arctic charr (AC) linkage groups (BW: AC-4, AC-20; CF: AC-7, AC-20, AC-23, AC-36; MAT: AC-13/34, AC-39). In addition to the genome-wide significant QTL for both BW and CF on AC-20, linkage groups AC-4, AC-7, AC-8, and AC-16 contain QTL for both BW and CF with chromosome-wide significance. These regions had effects (albeit weaker) on MAT with the exception of the region on AC-8. Comparisons with a North American cultured strain of Arctic charr, as well as North American populations of Atlantic salmon (Salmo salar), and rainbow trout (Oncorhynchus mykiss), reveal some conservation in QTL location and structure, particularly with respect to the joint associations of QTL influencing BW and CF. The detection of some differences in genetic architecture between the two aquaculture strains of Arctic charr may be reflective of the differential evolutionary histories experienced by these fishes, and illustrates the importance of including different strains to investigate genetic variation in a species where the intent is to use that variation in selective breeding programs.     

Effects of Fish-farm Activity on the Limnetic Community Structure of Brown Trout, Salmo trutta, and Arctic Charr, Salvelinus alpinus

Establishment of four fish-farms during the period 1971 to 1994 in the oligotrophic lake Skogseidvatnet affected Arctic charr, Salvelinus alpinus, but not brown trout, Salmo trutta. From 1971 to 1987, an increase in mean individual size of Arctic charr was recorded, while the mean individual size of brown trout remained stable. Arctic charr were found to use deeper benthic areas than brown trout. Approximately 8% of the Arctic charr population (>26cm), were found to switch to waste food from fish-farms, resulting in a novel feeding habitat for the species. They were, however, found in gillnets distant from the fish farm cages, indicating high mobility. The habitat segregation between the two species can most likely be explained by selective differences and asymmetric competition with brown trout as the dominant species. Based on the present results, changes in the Arctic charr population may be due to increased food availability and due to a new habitat use as a waste food feeder. The reason for the brown trout population to have remained stable with respect to mean size, growth pattern and habitat use, may be due to a different diet choice than Arctic charr in this lake. Brown trout were found to feed mainly on terrestrial insects, while Arctic charr fed mainly on zooplankton and on waste food.     

Diel food selection of pelagic Arctic charr, Salvelinus alpinus (L.), and brown trout, Salmo trutta L., in Lake Atnsjø, SE Norway

Patterns of diel food selection in pelagic Arctic charr, Salvelinus alpinus (L.) and brown trout, Salmo trutta L. were investigated in Lake Atnsjo, SE Norway, by gillnet sampling during July-September 1985. Arctic charr feed almost exclusively on zooplankton both day and night, while brown trout had a diurnal shift in diet. For this species zooplankton made up a considerable part of the diet in the daytime, while at night the diet consisted mainly of surface insect and chironomid pupae. Both species had a selective feeding mode on zooplankton during the day and night. Arctic charr had a higher gill raker number and a denser gill raker spacing compared with brown trout. Still, the differences in prey size between the two species were small. We argue that the observed differences in food selection between Arctic charr and brown trout can be explained by differing abilities to detect food items under low light conditions.     

Sex chromosome polymorphisms in Arctic charr and their evolutionary origins

Current data on the Y-specific sex-determining region of salmonid fishes from genera Salvelinus, Salmo, and Oncorhynchus indicate variable polymorphisms in the homologous chromosomal locations of the sex-specific determining region. In the majority of the Atlantic lineage Arctic charr, including populations from the Fraser River, in Labrador Canada, as well as Swedish and Norwegian strains, the sex-determining locus maps to linkage group AC-4. Previously, sex-linked polymorphisms (i.e., variation in the associated sex-linked markers on AC-4) have been described in Arctic charr. Here, we report further evidence for intraspecific sex linkage group polymorphisms in Arctic charr (i.e., the detection of the SEX locus on either the AC-1 or AC-21 linkage group) and a possible conservation of a sex linkage arrangement in Icelandic Arctic charr and Atlantic salmon, involving sex-linked markers on the AC-1/21 homeologs and the European AS-1/6 homeologous linkage groups in Atlantic salmon. The evolutionary origins for the multiple sex-determining regions within the salmonid family are discussed. We also relate the variable sex-determining regions in salmonids to their ancestral proto-teleost karyotypic origins and compare these findings with what has been observed in other teleost species in general.     

Selection on Arctic charr generated by competition from brown trout

We experimentally explored population‐ and individual‐level effects on Arctic charr (Salvelinus alpinus) resulting from resource competition with its common European competitor, the brown trout (Salmo trutta). At the population level, we compared performance of the two species in their natural sympatric state with that of Arctic charr in allopatry. At the individual level, we established selection gradients for morphological traits of Arctic charr in allopatric and in sympatric conditions. We found evidence for interspecific competition likely by interference at the population level when comparing differences in average performance between treatments. The growth and feeding rates did not differ significantly between allopatric and sympatric Arctic charr despite lower charr densities (substitutive design) in sympatric enclosures indicating that inter‐ and intraspecific competition are of similar strength. The two species showed distinct niche segregation in sympatry, and brown trout grew faster than Arctic charr. Arctic charr did not expand their niche in allopatry, indicating that the two species compete to a limited degree for the same resources and that interference may suppress the growth of charr in sympatric enclosures. At the individual level, however, we found directional selection in sympatric enclosures against individual Arctic charr with large head and long fins and against individuals feeding on zoobenthos rather than zooplankton indicating competition for common resources (possibly exploitative) between trout and these charr individuals. In allopatric enclosures these relations were not significant. Diets were correlated to the morphology supporting selection against the benthic‐feeding type, i.e. individuals with morphology and feeding behaviour most similar to their competitor, the benthic feeding brown trout. Thus, this study lends support to the hypothesis that Arctic charr have evolved in competition with brown trout, and through ecological character displacement adapted to their present niche.     

Spatial and temporal distributions of salmonids in two ponds in Newfoundland, Canada

Spatial and temporal distributions of salmonids were examined in Junction Pond, Northeast River, Placentia and Conne Pond, Conne River, Newfoundland using Lundgren multiple-mesh experimental gillnets. Both ponds contain populations of Atlantic salmon and brook trout with Junction Pond also possessing brown trout and resident Arctic charr. For salmon parr there was a significant month effect in distribution of catch rates in both ponds, and in Junction Pond, there was a significant diel effect. There was also significant variation in catch rates by lentic zone. For brook trout, there was a significant lentic zone × month interaction in Junction Pond; in Conne Pond, the main effects lentic zone and month were significant. Highest benthic catch rates of Atlantic salmon parr occurred in the littoral zone of both ponds. Most captures of brook trout also occurred benthically in both ponds; similar to salmon parr, littoral zone catch rates were higher than those of the deeper benthic area in Conne Pond but the reverse was true for Junction Pond. For both salmon parr and brook trout, the deeper benthic area and the pelagic area were relatively important rearing habitats in each pond. The distribution of catches for brown trout (few in number relative to the other species) in Junction Pond was similar to that of brook trout while Arctic charr were found mainly pelagically. Within the benthic area, most Arctic charr were caught at depths beyond the littoral zone. There was a tendency for Altantic salmon parr and brook trout found in the deeper benthic area and the pelagic area to be significantly larger and older than those in littoral zone in each pond. Sizes of Arctic charr did not differ significantly among lentic zones.     

The most variable vertebrate on Earth

In the search for the most variable non-human vertebrate on Earth, intraspecific variation of ten variable traits was compared among ten highly variable species. Mammals, birds and many reptiles, amphibians and fishes were excluded because most of the variation is among, and not within species. The focus was on northern fishes, where high intraspecific variation is well documented. The ten selected species were European whitefish Coregonus lavaretus, chinook salmon Oncorhyncus tshawytscha, sockeye salmon O. nerka, rainbow trout O. mykiss, atlantic salmon Salmo salar, brown trout S. trutta, arctic charr Salvelinus alpinus, brook charr S. fontinalis, dolly varden charr S. malma and threespine stickleback Gasterosteus aculeatus. Variation included not only size and phenotype, but also ecology, behaviour and life history. The traits were geographic range, migration, habitat, adult size, colour, body form, polymorphism, diet, reproduction and genetics. Arctic charr came on top in the final ranking, followed by dolly varden charr and rainbow trout. The two least variable were chinook salmon and threespine stickleback. It is proposed that arctic charr, which is also the northernmost fish on Earth, has evolved its unique variability in range, size, phenotype, ecology and life history by adapting to the extreme and highly unpredictable ecological conditions of arctic and other northern lakes for many glacial periods.     

Winter ecology of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in a subarctic lake,Norway

We studied habitat choice, diet, food consumption and somatic growth of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) during the ice-covered winter period of a subarctic lake in northern Norway. Both Arctic charr and brown trout predominantly used the littoral zone during winter time. Despite very cold winter conditions (water temperature <1°C) and poor light conditions, both fish species fed continuously during the ice-covered period, although at a much lower rate than during the summer season. No somatic growth could be detected during the ice-covered winter period and the condition factor of both species significantly declined, suggesting that the winter feeding rates were similar to or below the maintenance requirements. Also, the species richness and diversity of ingested prey largely decreased from summer to winter for both fish species. The winter diet of Arctic charr <20 cm was dominated by benthic insect larvae, chironomids in particular, and Gammarus lacustris, but zooplankton was also important in December. G. lacustris was the dominant prey of charr >20 cm. The winter diet of brown trout <20 cm was dominated by insect larvae, whereas large-sized trout mainly was piscivorous, feeding on juvenile Arctic charr. Piscivorous feeding behaviour of trout was in contrast rarely seen during the summer months when their encounter with potential fish prey was rare as the small-sized charr mainly inhabited the profundal. The study demonstrated large differences in the ecology and interactions of Arctic charr and brown trout between the winter and summer seasons.