Metazoan arasites of fish from the Smallwood Reservoir, Labrador, Canada

Three-hundred and thirty-two fish of eight species (5 Salmo salar , 68 Salvelinus fontinalis , 32 S. namaycush , 102 Coregonus clupeaformis , 1 Prosopium cylindraceum , 107 Esox lucius , 14 Catostomus catostomus , 3 Couesius plumbeus ) from the Smallwood Reservoir, Labrador, Canada, were examined for metazoan parasites, using conventional parasitological techniques.
Fifteen genera of parasites were recovered (two of Monogenea, two of Digenea, four of Cestoda, three of Nematoda, two of Acanthocephala and two of Copepoda), these including seven new host records.
Significant differences were noted in the prevalence of the various parasites which were common to the different species of fish examined. No differences were recorded in the parasite burden of male and female fish. There was no correlation between the number of parasite species per infected fish and host age except in the case of Salvelinus namaycush . Food items of the fish examined were also noted.     

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.     

Changes in the North Channel fish community,with emphasis on pink salmon (Oncorhynchus gorbuscha Walbaum)

Historical trends in commercial fishery yields were examined for evidence of structural changes in the North Channel fish community. Significant declines in the abundance of indigenous species occurred primarily as a result of man's activities. Lake sturgeon (Acipenser fulvescens Rafinesque) were harvested down to low levels by 1900. Introductions of exotics to the fish community were associated with major changes. Rainbow smelt (Osmerus mordax Mitchill) and sea lamprey (Petromyzon marinus Linnaeus) colonized the channel in the late 1930s. Concurrently, lake trout (Salvelinus namaycush Walbaum) and burbot (Lota lota Linnaeus), the top deepwater predators, declined to near extinction. Lake whitefish (Coregonus clupeaformis Mitchill) and shallow-water cisco (Coregonus artedii Lesueur) also declined. Without predation pressure, smelt abundance increased to high levels in the 1950s and alewife (Alosa pseudoharengus Wilson), another exotic, peaked during the 1960s. Both species equilibrated at lower levels in the 1970s, perhaps favouring colonization by pink salmon (Oncorhynchus gorbuscha Walbaum). Pink salmon which are larger and more fecund in Lake Huron than in Lake Superior, are increasing rapidly in numbers and are expanding their range in the channel. Certain whitefish stocks have increased sufficiently to support fishery yields greater than those of the 1930s, despite considerable exploitation pressure. This success is partially in response to the control of sea lamprey since 1961. However both lake whitefish and walleye (Stizostedion vitreum Mitchill) are now rare in the east end of the channel, possibly due to environmental factors such as acid precipitation and metal contaminants. Community stability will not likely be attained until a suitable climax predator becomes reestablished.     

Effect of landscape factors on fish distribution in arctic Alaskan lakes

1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape‐level factors that control colonisation and extinction. 2. We used classification and regression tree (CART) analyses to quantify the importance of landscape‐level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables). 3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied with species. Extinction variables were most important for lake trout (Salvelinus namaycush) and slimy sculpin (Cottus cognatus), a mixture of extinction and colonisation variables was important for arctic char (Salvelinus alpinus), and colonisation variables were most important for arctic grayling (Thymallus arcticus) and round whitefish (Prosopium cylindraceum). 4. Ecological differences among species account for much of the difference in relative importance of colonisation versus extinction variables. In addition, stream piracy events have occurred over geologic time scales, which have resulted in lakes that are currently inaccessible but support relict fish populations. 5. Climate warming, currently occurring in the arctic, is likely to alter further the stream network, which could have dramatic effects on fish distributions by affecting access to isolated lakes or isolating lakes that are currently accessible.     

Peculiarities of the parasitofauna of Atlantic salmon parr (Salmo salar L.), brown trout (Salmo truttae L.), and char (Salvelinus alpinus L.) in the Utsjoki River system (Northern Finland)

Data on the parasite diversity in Salmonidae fish parr from different parts of the Utsjoki River obtained during 1993-1995 and 2006-2007 are presented. Three fish species, Salmo salar L., S. truttae L., and Salvelinus alpinus L., were examined on the presence of helminthes. Twenty species of salmon parasites were found, the majority of which are the parasites with complicated life cycles. Infusorians C apriniana piscium, myxosporidia Chloromyxum januaricus and Myxobolus neurobius, metacercaria of the genera Diplostomum and Apatemon, and the nematode Raphidascaris acus larvae were the most numerous in salmon parasite fauna. Brown trout had the most number of specific parasite species, whereas char was infested by protozoan parasites only.     

Seasonal dietary shifts enhance parasite transmission to lake salmonids during ice cover

Changes in abiotic and biotic factors between seasons in subarctic lake systems are often profound, potentially affecting the community structure and population dynamics of parasites over the annual cycle. However, few winter studies exist and interactions between fish hosts and their parasites are typically confined to snapshot studies restricted to the summer season whereas host‐parasite dynamics during the ice‐covered period rarely have been explored. The present study addresses seasonal patterns in the infections of intestinal parasites and their association with the diet of sympatric living Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in Lake Takvatn, a subarctic lake in northern Norway. In total, 354 Arctic charr and 203 brown trout were sampled from the littoral habitat between June 2017 and May 2018. Six trophically transmitted intestinal parasite taxa were identified and quantified, and their seasonal variations were contrasted with dietary information from both stomachs and intestines of the fish. The winter period proved to be an important transmission window for parasites, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through fish prey in brown trout. In Arctic charr, seasonal patterns in parasite infections resulted mainly from temporal changes in diet toward amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout. The overall dynamics in the community structure of parasites chiefly mirrored the seasonal dietary shifts of their fish hosts.     

The association between parasite infection and growth rates in Arctic charr: do fast growing fish have more parasites?

Trophically transmitted parasites are known to impair fish growth in experimental studies, but this is not well documented in natural populations. For Arctic charr [Salvelinus alpinus (L.)], individual growth is positively correlated with food consumption. However, increased food consumption will increase the exposure to trophically transmitted parasites. Using a correlative approach, we explore the association between parasite abundance and the individual growth of Arctic charr from five lakes within the same watercourse. The studied parasite species differ in their life cycles and cost to the host. We predicted a positive association between parasite abundance and fish growth for parasites of low pathogenicity reflecting high consumption rates, and a negative association at higher parasite abundances for more costly parasites. We found no direct negative associations between parasite abundance and fish growth. The relationship between parasite abundance and growth was linearly positive for the low costly Crepidostomum sp. and concave for the more costly Eubothrium salvelini. In natural fish populations, the negative effects of parasites on fish growth might be outweighed by the energy assimilated from feeding on the intermediate host. However, experimental studies with varying food consumption regimes are needed to determine the mechanisms underlying our observations.

     

Fine-Scale Ecological and Genetic Population Structure of Two Whitefish (Coregoninae) Species in the Vicinity of Industrial Thermal Emissions

Thermal pollution from industrial processes can have negative impacts on the spawning and development of cold-water fish. Point sources of thermal effluent may need to be managed to avoid affecting discrete populations. Correspondingly, we examined fine-scale ecological and genetic population structure of two whitefish species (Coregonus clupeaformis and Prosopium cylindraceum) on Lake Huron, Canada, in the immediate vicinity of thermal effluent from nuclear power generation. Niche metrics using δ¹³C and δ¹⁵N stable isotopes showed high levels of overlap (48.6 to 94.5%) in resource use by adult fish captured in areas affected by thermal effluent compared to nearby reference locations. Isotopic niche size, a metric of resource use diversity, was 1.3- to 2.8-fold higher than reference values in some thermally affected areas, indicative of fish mixing. Microsatellite analyses of genetic population structure (F_st, STRUCTURE and DAPC) indicated that fish captured at all locations in the vicinity of the power plant were part of a larger population extending beyond the study area. In concert, ecological and genetic markers do not support the presence of an evolutionarily significant unit in the vicinity of the power plant. Thus, future research should focus on the potential impacts of thermal emissions on development and recruitment.     

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.     

Effects of the eye fluke Diplostomum spathaceum on the energetics and feeding of Arctic charr Salvelinus alpinus

In the present study, effects of the trematode eye fluke Diplostomum spathaceum infection and parasite‐induced cataract on energetic costs and feeding of hatchery‐bred one‐summer‐old Lake Saimaa Arctic charr Salvelinus alpinus were examined. The energetic effects (measured as oxygen uptake) of acute eye fluke infection on S. alpinus were negligible, but in the chronic infections mean oxygen consumption of infected fish was significantly higher than that of controls. Feeding capability of S. alpinus was studied in aquarium experiments, and uninfected healthy‐eyed fish reacted to zooplankton more rapidly and caught zooplankton with better success compared to individuals with cataracts in the same school. The results suggested that to compensate energetic costs and impaired feeding capability caused by eye fluke, cataract‐bearing fish spend more time foraging, which may result in increased predation risk.     

Water temperatures influence the marine area use of Salvelinus alpinus and Salmo trutta

The migratory behaviour and spatial area use of sympatric Arctic charr Salvelinus alpinus and brown trout Salmo trutta were investigated during their marine feeding migration. The likelihood of finding individuals of both species in the inner or outer fjord areas was dependent on water temperature in the inner area (especially for S. alpinus), the temperature difference between the inner and outer areas (especially for S. trutta) and fish fork length (both species). The strongest predictor was the water temperature in the inner area, and particularly S. alpinus left this area and moved to the outer areas with increasing temperatures in the inner area. At 8° C in the inner area, the likelihood of finding S. alpinus in the outer areas was >50%. This predictor had a smaller effect on S. trutta, and the likelihood of finding S. trutta in the outer areas only started to increase at around 14° C. The relationships between temperature and area use did not correspond to the species' optimal growth temperatures, but to their previously documented temperature preferences. Individuals of both species used mainly the littoral fjord areas, and to a lesser extent the pelagic areas. In conclusion, temperature differences between the inner and outer marine areas probably resulted in the segregated area use between the species, because water temperatures or factors influenced by temperature affected their migratory behaviour and habitat use differently. The results indicate that increased marine temperatures with global warming may lead to increased spatial overlap between S. trutta and S. alpinus, which again may lead to increased interspecific competition during their marine phase, and with S. alpinus probably being the more negatively affected.     

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.     

Non-native species and lake warming negatively affect Arctic char Salvelinus alpinus abundance; deep thermal refugia facilitate co-existence

This study finds that non-native species and warming temperatures have significant negative effects on Arctic char Salvelinus alpinus abundance in Irish lakes. Eutrophication was not important at the range of total phosphorus tested (0.005–0.023 mg l⁻¹). Model results predict that S. alpinus occur across the temperature range sampled (8.2–19.7°C) when non-natives are absent, but S. alpinus catch is predicted to be close to zero irrespective of temperature when non-native catch is high. This result indicates that to persist, S. alpinus may require a habitat where non-natives are at low abundance or absent. Salvelinus alpinus segregated from other species along the thermal axis, inhabiting significantly colder water and actively avoided non-native species, which appeared to limit their distribution. The thermal niche realized by S. alpinus in non-native dominated lakes was thus compressed relative to native dominated lakes and S. alpinus population density was significantly lower. These findings were consistent even when the only non-native present was Perca fluviatilis. Temperature appeared to limit the distribution of non-native species, such that the presence of deep thermal refugia is currently facilitating S. alpinus co-existence with non-natives in associated lakes. Diet analysis identified P. fluviatilis as potential predators and competitors. This study provides strong evidence that non-native species are a key driver of low S. alpinus abundance in Irish lakes. Temperature increases associated with climate change are identified as a secondary concern, as they could erode S. alpinus' thermal niche and lead to their extirpation. The lower thermal buffering capacity of shallow lakes identifies these as higher risk systems. Salvelinus alpinus conservation in Ireland should focus on preventing future illegal non-native species introductions because unlike other stressors (e.g., eutrophication etc.), species introductions are rarely reversible.     

Interspecific Relationships among Charrs Based on Phylogenetic Analysis of Nuclear Growth Hormone Intron Sequences

DNA samples were obtained from six charr species: Salvelinus alpinus, S. malma, S. confluentus, S. leucomaenis, S. namaycush and S. fontinalis and two outgroups: Salmo salar and S. trutta. The C and D introns from the duplicate growth hormone loci (GH1 and GH2) were amplified using the polymerase chain reaction and sequenced from each of the species. Phylogenetic analyses with and without gaps were performed using the beta version of PAUP. The GH introns are evolving relatively slowly, so the data were combined with sequences from the ITS1 and ITS2 for a phylogenetic analysis of the charr species. The GH intron data and the combined data supported two groups of sister species among charrs: S. alpinus and S. malma, and S. confluentus and S. leucomaenis.     

Fatty acid composition of fish species with different feeding habits from an Arctic Lake

We compared the composition and content of fatty acids (FAs) in fish with different feeding habits (sardine (least) cisco Coregonus sardinella, goggle-eyed charr (pucheglazka) form of Salvelinus alpinus complex, humpback whitefish Coregonus pidschian, broad whitefish Coregonus nasus, boganid charr Salvelinus boganidae, and northern pike Esox lucius from an Arctic Lake. Feeding habits of the studied fish (planktivore, benthivore, or piscivore) significantly affected the composition of biomarker fatty acids and the ratio of stable isotopes of carbon and nitrogen in their biomass. The hypothesis on a higher content of eicosapentaenoic and docosahexaenoic acids in the fish of higher trophic level (piscivores) when compared within the same taxonomic group (order Salmoniformes) was confirmed.     

Mercury accumulation in five species of freshwater fish in Lake Tyrifjorden,south-east Norway,with emphasis on their suitability as test organisms

Synopsis Mercury concentration in axial muscle of brown trout, Salmo trutta, whitefish, Coregonus lavaretus, Arctic charr, Salvelinus alpinus, smelt, Osmerus eperlanus and pike, Esox lucius, were studied in Lake Tyrifjorden during 1978–1982. Our data demonstrate that older and bigger fish on an average have higher mercury concentration than smaller and younger. Further, complex life histories as in brown trout influence the pattern of mercury accumulation. During young stages accumulation in brown trout is moderate, while accumulation in older stages is highly correlated to lake residency time. Based on our data we suggest the following requirements for a test organism and the collecting procedure; (1) life history should be simple with small sexual differences, (2) ageing should be easy and reliable, and (3) large representative samples should be easily obtained during (4) a fixed biological period i.e. the spawning period. We consider smelt as an appropriate test organism based on these criteria.     

The effects of dredging and fish stocking on the trophic status of shallow,peaty ditches

Size selective predation on molluscs was apparent for lake trout (Salvelinus namaycush) and round whitefish (Prosopium cylindraceum), but not for arctic grayling (Thymallus arcticus), in the Toolik Lake region of arctic Alaska during the summer of 1986. Lake trout consumed significantly larger molluscs of all taxa than did round whitefish, and selected larger molluscs than were available on either rocky or soft-sediment habitats. Round whitefish were not size-selective on the snail Lymnaea, but were size-selective on the snail Valvata and on clams from the soft sediments. Round whitefish consumed fewer and smaller Lymnaea compared to lake trout. Because lake trout ate more Lymnaea and also tended to select larger, reproductive-sized individuals, this fish could potentially have a more detrimental impact on the Lymnaea population. Finally, differences in Lymnaea densities and size distributions between lakes with and without lake trout suggest that these fish may be responsible for the pattern of distribution, size, and density observed for Lymnaea in Toolik Lake and other area lakes.     

Exogenous control of diel locomotor activity in the whitefish Coregonus clupeaformis: effects of light and temperature

Summary Data on factors determining activity cycles of nearctic fishes are scarce overall, and nonexistent for Coregoniae (family Salmonidae), a group with closely related and somewhat better known palaearctic species. We studied effects of photoperiodicity, light intensity and temperature on diel locomotor activity of lake whitefish Coregonus clupeaformis (Mitchill). Under LD 12:12, a day-active pattern was evident. Under continuous light (LL) and continuous dark (DD), rhythmicity was greatly suppressed or absent, respectively. Day-time activity levels were positively correlated with illuminance over the range tested (0.005 to 500 lux). At the three temperatures tested, activity was lowest at 7° C, highest at 12° C (a reported temperature optimum), and intermediate at 17° C. Our results suggest that level and diel pattern of lake whitefish activity are under overriding external control, and we find similarities with published data on the European species Coregonus lavaretus.     

The Microbiota of Freshwater Fish and Freshwater Niches Contain Omega-3 Fatty Acid-Producing Shewanella Species

Approximately 30 years ago, it was discovered that free-living bacteria isolated from cold ocean depths could produce polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) (20:5n-3) or docosahexaenoic acid (DHA) (22:6n-3), two PUFA essential for human health. Numerous laboratories have also discovered that EPA- and/or DHA-producing bacteria, many of them members of the Shewanella genus, could be isolated from the intestinal tracts of omega-3 fatty acid-rich marine fish. If bacteria contribute omega-3 fatty acids to the host fish in general or if they assist some bacterial species in adaptation to cold, then cold freshwater fish or habitats should also harbor these producers. Thus, we undertook a study to see if these niches also contained omega-3 fatty acid producers. We were successful in isolating and characterizing unique EPA-producing strains of Shewanella from three strictly freshwater native fish species, i.e., lake whitefish (Coregonus clupeaformis), lean lake trout (Salvelinus namaycush), and walleye (Sander vitreus), and from two other freshwater nonnative fish, i.e., coho salmon (Oncorhynchus kisutch) and seeforellen brown trout (Salmo trutta). We were also able to isolate four unique free-living strains of EPA-producing Shewanella from freshwater habitats. Phylogenetic and phenotypic analyses suggest that one producer is clearly a member of the Shewanella morhuae species and another is sister to members of the marine PUFA-producing Shewanella baltica species. However, the remaining isolates have more ambiguous relationships, sharing a common ancestor with non-PUFA-producing Shewanella putrefaciens isolates rather than marine S. baltica isolates despite having a phenotype more consistent with S. baltica strains.     

Development of a species-specific fractionation equation for Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis> (L.)): an experimental approach

A species-specific fractionation equation for Arctic charr (Salvelinus alpinus (L.)) was developed experimentally for use in ecological studies of temperature-driven phenologies for the species. Juvenile Arctic charr were reared in controlled conditions at different temperatures (2–14°C), with three replicates of each temperature. Otoliths from the fish and water samples from the chambers were analysed for oxygen isotope composition and used to estimate temperature-dependent fractionation equations relating the isotopic ratio to rearing temperature. A linear and a second order polynomial relationship were estimated and validated using comparable Arctic charr data from another study. Temperatures predicted using the polynomial equation were not significantly different from recorded experimental temperatures, whereas with the linear equation there were significant differences between the predicted and measured temperatures. The polynomial equation also showed the least bias as measured by mean predictive error. Statistical comparisons of the polynomial fractionation equation to a similarly estimated equation for brook charr (Salvelinus fontinalis (Mitchill)) indicated significant differences. Results imply the need for species-specific fractionation equations, even for closely related fish. Results further suggest the polynomial form of the fractionation equation will facilitate more accurate characterisation of water temperatures suitable for use in ecological studies of temperature-driven phenologies of Arctic charr.