The parasite fauna of the fish of the Shropshire Union Canal, Cheshire

A survey was made of the parasites of 603 roach Rutilus rutilus (L.), 15 bream Abramis brama (L.), 201 perch Perca fluviatilis L., 30 pike Esox lucius L. and four eels Anguilla anguilla (L.) caught in the Shropshire Union Canal at Backford, Cheshire from December 1964 to August 1966. Twenty-seven species of parasites were found, 17 in roach, seven in bream, ten in perch, ten in pike and two in the eel. Two species of Protozoa, seven species of Monogenea, five species of Digenea, six species of Cestoda, two species of Nematoda, one species of Acanthocephala, two species of Hirudinea, one species of Crustacea and mollusc glochidia were recorded. The following parasites are believed to be new records for the British Isles: Henneguya oviperda (Cohn, 1895), Dactylogyrus suecicus Nybelin, 1936, D. wunderi Bykhovskii, 1931, Asymphylodora kubanicum (Isaichikov, 1923), and Philometra rischta Skryabin, 1917.
One table shows the species of parasites found, together with data on the site of occurrence in the host, and the percentage and intensity of infection of the fish. A second table compares the occurrence of the parasites in four other localities in the British Isles, Loch Lomond Scotland, Llyn Tegid (Bala Lake), Merionethshire, Rostherne Mere, Cheshire and the River Lugg, Herefordshire. A further column gives the normal hosts in the U.S.S.R.
A limited comparison is made of the numerical occurrence of six species of parasites in the canal, Llyn Tegid and Druzno Lake, Poland. It is concluded that unless relatively large samples of fish of all length groups are collected on a regular basis throughout the year such comparisons will have little meaning.
The concept of the characterization of parasite faunas is briefly noted. It is suggested that the high degree of host specificity shown by many of the species of parasites is evidence in support of the concept.     

Invasion character and distribution of the Diplostomum huronense (La Rue, 1927) Hugnes, 1929 metacercariae in roach of Lake Ladoga

Estimation of the invasion character and distribution of the Diplostomum huronense metacercariae depending on the fish host age has been carried out in roach of Lake Ladoga. Distribution of D. huronense in the young roach (up to age 5+) is negative binomial. Aggregation of the parasite is caused not only by individual differences in the fish host resistance to the metacercariae invasion, but by a high mortality of hyperinfected fishes as well. In older individual hosts the host-parasite system is destroyed, and the parasite distribution approximates to normal. The parasite system of the diplostomids in roach is characterized by the spatial asymmetry, when most part of parasites inhabit few individual hosts, and probability of the case when a parasite get into previously infected host is higher than that of the invasion of parasite-free host. Thus, the Diplostomum huronense metacercaria is an important factor regulating the fish fry number both in direct (death of infected fry) and indirect (elimination of hyperinfected fishes by ichthyophagous birds) way.     

Molecular faunistics of accidental infections of <Emphasis Type="Italic">Gyrodactylus</Emphasis> Nordmann, 1832 (Monogenea) parasitic on salmon <Emphasis Type="Italic">Salmo salar</Emphasis> L. and brown trout <Emphasis Type="Italic">Salmo trutta</Emphasis> L. in NW Russia

Salmon Salmo salar L. and brown trout S. trutta L. juveniles were examined for the presence of accidental monogenean ectoparasitic species of Gyrodactylus Nordmann, 1832 in the Baltic and White Sea basins of Russian Karelia in order to estimate the frequency of host-switching attempts on an ecological timescale. To collect phylogeographical information and for exact species identification, the parasites were characterised by nuclear internal transcribed spacer sequences of rDNA (ITS) and, for some species, also by their mitochondrial DNA (CO1 gene) sequences. Four accidental Gyrodactylus species were observed on salmon and brown trout. A few specimens of G. aphyae Malmberg, 1957, the normal host of which is the Eurasian minnow Phoxinus phoxinus (L.), were observed on lake salmon from the Rivers Kurzhma (Lake Kuito, White Sea basin) and Vidlitsa (Lake Ladoga, Baltic basin). G. lucii Kulakovskaya, 1952, a parasite of the northern pike Esox lucius L., was observed on salmon in the Kurzhma. In the River Vidlitsa, two specimens of G. papernai Ergens & Bychowsky, 1967, normally on stone loach Barbatula barbatula (L.), were found on salmon. On anadromous White Sea salmon in the River Pulonga in Chupa Bay, a few salmon parr carried small colonies of G. arcuatus Bychowsky, 1933, which were shown to have originated from the local three-spined stickleback Gasterosteus aculeatus L. consumed as prey. No specimens of Gyrodactylus salaris Malmberg, 1957 were observed, although the Pulonga is the nearest salmon spawning river to the River Keret', which is heavily infected with introduced G. salaris. In the River Satulinoja, Lake Ladoga, three specimens of G. lotae Gusev, 1953, from burbot Lota lota (L.), were collected from a single brown trout S. trutta. All nonspecific gyrodactylid infections on salmonids were judged to be temporary, because only a few specimens were observed on each of the small number of infected fishes. The prevalence of endemic G. salaris was also low, only 1% (Nfish = 296) in Lake Onega and 0.7% (Nfish = 255) in Lake Ladoga, while brown trout specific Gyrodactylus species were not observed on any of the 429 trout examined from the Ladoga basin. The host-specific and unspecific burden of Gyrodactylus spp. on these 'glacial relict' populations of salmon and brown trout was very low, suggesting a generalised resistance against the co-evolved freshwater parasite community, or some kind of 'vaccination' effect. These hypotheses deserve further testing.     

Demographic histories and genetic diversities of Fennoscandian marine and landlocked ringed seal subspecies

Island populations are on average smaller, genetically less diverse, and at a higher risk to go extinct than mainland populations. Low genetic diversity may elevate extinction probability, but the genetic component of the risk can be affected by the mode of diversity loss, which, in turn, is connected to the demographic history of the population. Here, we examined the history of genetic erosion in three Fennoscandian ringed seal subspecies, of which one inhabits the Baltic Sea ‘mainland’ and two the ‘aquatic islands’ composed of Lake Saimaa in Finland and Lake Ladoga in Russia. Both lakes were colonized by marine seals after their formation c. 9500 years ago, but Lake Ladoga is larger and more contiguous than Lake Saimaa. All three populations suffered dramatic declines during the 20th century, but the bottleneck was particularly severe in Lake Saimaa. Data from 17 microsatellite loci and mitochondrial control‐region sequences show that Saimaa ringed seals have lost most of the genetic diversity present in their Baltic ancestors, while the Ladoga population has experienced only minor reductions. Using Approximate Bayesian computing analyses, we show that the genetic uniformity of the Saimaa subspecies derives from an extended founder event and subsequent slow erosion, rather than from the recent bottleneck. This suggests that the population has persisted for nearly 10,000 years despite having low genetic variation. The relatively high diversity of the Ladoga population appears to result from a high number of initial colonizers and a high post‐colonization population size, but possibly also by a shorter isolation period and/or occasional gene flow from the Baltic Sea.     

Gill anomalies of perch and roach from four lakes differing in water quality

This study examined gill anomalies of two common freshwater fish species, roach Rutilus rutilus and perch Perca fluviatilis , collected over five seasons in 1989–1990 from four lakes in central Finland. The lakes differed both in water quality and in fish parasite species composition. Particular attention was paid to the differences in chloride cell proliferation. Gill anomalies were generally more common and abundant in roach than in perch. Chloride cell proliferation was the most frequent histological change in roach but was that least often found in perch. Most of the changes were systemic and light in severity. In perch an unidentified lesion of noncellular eosinophilic inclusions in an enlarged epithelium was also recorded. There was a marked pattern in the severity of histological changes in perch when comparing those from the natural Lake Peurunka to those from three 'altered' lakes. Gills of perch from Lake Peurunka possessed more alterations in all the recorded parameters. In roach, a significant differences were detected in chloride cell and epithelial proliferation: these were greater in Lake Peurunka and 'polluted' Lake Vatia. In perch, all histological changes were significantly more frequent at the end of autumn 1989 when compared to other seasons. In roach, increased frequencies of all gill changes were noted in winter and spring samples. Tissue reactions to parasites were either only localized or absent. The systemic gill alterations in freshwater fish may reflect the soft nature and low winter temperature of Finnish fresh waters, in which chemical imbalances, such as acid peaks, may induce more dramatic changes in fish tissues than in harder waters.     

Dependence that the community structure of the roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) parasites has on the host age

The changes that take place in the structure of the parasite communities of two roach populations as the hosts grow older have been studied in the Chivyrkuiskii Bay of Lake Baikal and the estuary of the Selenga River. The parasite communities are analyzed at the levels of host individuals (infracommunities), host age groups (sets of infracommunities), and host population (component community). The number of parasite species regularly increases as the roaches age in both aquatic bodies, whereas the evenness of the parasite communities decreases. The Berger-Parker dominance index of the parasite communities changes with the roach age in different directions, increasing in the Chivyrkuiskii Bay and decreasing in the estuary of the Selenga River. The changes in the Shannon diversity index for sets of infracommunities of roach parasites are the opposite of those in the Berger-Parker index.     

Shoreline displacement of Lake Ladoga — new data from Kilpolansaari

Dating of sediments sampled from small lakes in the Kilpolansaari region, in the NW part of Lake Ladoga, indicate that the River Neva, which is the present outlet of Lake Ladoga, originated at 3,100 radiocarbon years BP This is in agreement with some earlier estimations but no consensus concerning the age of the River Neva has previously been reached. New diatom data provide information concerning salinity and nutrient conditions in northern Lake Ladoga prior to the formation of the River Neva, when the Litorina Sea occupied the Baltic basin and approached the level of the ancient Lake Ladoga. Some slightly brackish water diatom species may indicate occasional saline water incursions into the Ladoga basin but, on the other hand, slightly brackish water species also occur in the present Lake Ladoga.     

Trematode fauna patterns of the freshwater fish on the border of the geographical range

The trematode fauna of the fishes inhabiting Lake Ladoga are represented by forty-six species; nine species of which are found here on the northern boudary of their geographic range. The depauperization of the trematode fauna compared to the southern pools is a result both of the decreasing impact of the Pont-Caspian group and of the introduction of the boreal piedmont species complex. The increase in the biological productivity of Lake Ladoga for the last 50-year period leads to enrichment of the species biodiversity. The same process increases the invasion extensiveness by trematodes, which use fish as an intermediate host. The Diplostomida, the presence of which is crucial for the young fish survival rate, dominate among the trematodes.     

Rapid changes in fish community structure and habitat distribution following the precipitation of lake phosphorus with aluminium

1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in‐lake phosphorus concentrations from 280 to 37 μg P L^?1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large‐bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.     

Formation of parasite fauna in the bullhead (Cottus gobio L.) (Pisces: Cottidae)

The formation of parasite fauna in the bullhead Cottus gobio L. in different water bodies was examined. The largest number of parasite species including specific parasites was observed in the Onega and Ladoga lakes. It is suggested that the host and their parasites migrated namely from these water bodies to other part of the range of the bullhead.     

The population biology of two species of eyefluke, Diplostomum spathaceum and Tylodelphys clavata, in roach and rudd

Infections of roach ( Rutilis rutilus ), and rudd ( Scardinius erythrophthalmus ), by the eyeflukes Diplostomun spathaceum and Tylodelphys clavata were studied in a lake over a three year period. T. clavata first appeared at the beginning of the study. Roach were heavily infected by both parasites, whereas the rudd contained very few specimens of either species. A small number of roach-rudd hybrids were also examined, and appeared to have a susceptibility intermediate between the parental types.
Levels of T. clavata in roach increased throughout the study. This parasite had a life span of a year or less in the fish, and was continuously lost from the population. This loss was balanced by a minor infection period in April/May and a major one extending from August until January. The fish continued to accumulate infections until they reached a size of about 130 mm, but thereafter intensity fluctuated about the level reached.
D. spathaceum infections similarly increased throughout the period of study, and there was a suggestion of a wave of infection in the spring. This parasite has a much longer life span, and levels of infection increased with fish size, only falling in the largest, and therefore oldest, hosts.
The major changes in the parasite populations in the roach were reflected, to a lesser extent, in the rudd. Both species were over-dispersed, but the data from roach was too heterogeneous to fit to any theoretical models, whereas that from the rudd was found to conform to a Negative Binomial distribution.     

A search for introgressive hybridization in the rudd, Scardinius erythrophthalmus (L.), and the roach, Rutilus rutilus (L.)

Rudd, roach and their hybrids from an interbreeding population at Norwich were examined electrophoretically for seven enzymes; an examination of pharyngeal teeth supplemented the data. The rudd were compared to rudd from Lake Trawsfynydd, Wales, a lake free from roach. No differences were observed between the rudd from the two localities and no evidence was found of introgression within the fish from Norwich.     

Changes in genetic structure of North American Bythotrephes populations following invasion from Lake Ladoga, Russia

1. We used allozyme electrophoresis to compare Bythotrephes longimanus (Crustacea: Onychopoda: Cercopagididae) from recently founded North American populations with those from native European populations, and to examine changes in genetic structure of North American populations over time.
2. The genetic structure of North American populations in 1996 was similar to that of European populations, because of the disappearance of founder effects which distinguished North American from European populations in 1989.
3. The Lake Ladoga, Russia population was more closely related to North American populations than to other European populations, consistent with non-genetic evidence implicating Lake Ladoga as the source of North American populations.
4. Our results provide additional evidence of the presence of an invasion corridor that allows Urasian and Ponto-Caspian species to be introduced into North American freshwater ecosystems, and show that founder effects can erode over time following establishment of invasive species.     

Feeding migration of roach, Rutilus rutilus (L.), in Lake Arungen, Norway

In the period April–July 1980 we studied the feeding migration and food of roach in a small tributary of the eutrophic Lake Årungen, south-eastern Norway. Tagging experiments revealed a tendency in roach to utilize a specific tributary both for feeding and for spawning. The mean size of roach ascending the tributary in late June and July was significantly larger than the mean size of roach spawning 1–2 months earlier, probably due to higher water discharge in July than in May and June. The experiment indicates two separately motivated migrations involving homing. The roach fed more profitably in the tributary than in the lake, both in terms of food availability and predator avoidance.     

Establishment of the Baikalian endemic amphipod Gmelinoides fasciatus Stebb. in Lake Ladoga

Gmelinoides fasciatus Stebb., a small amphipod from the Lake Baikal basin, was discovered in July 1988 in Lake Ladoga, the largest European lake. G. fasciatus likely invaded Lake Ladoga as a consequence of its intentional introduction, aimed at enhancing fish production, in some Karelian Isthmus lakes close to Lake Ladoga's western shore in the early 1970's. Benthos studies conducted in 1989 and 1990 revealed that G. fasciatus was well established in littoral communities along the western and northern shores of Lake Ladoga. G. fasciatus was the dominant species in these littoral communities and contributed over 70% of the macroinvertebrate biomass. The species was abundant in different macrophyte beds and stony littoral areas, both in heavily polluted and undisturbed sites. The maximum abundance and biomass of G. fasciatus was about 54,000 ind m^–2 and 160 g (wet wt.) m^–2. Negative impacts of G. fasciatus on native species have been observed. Studies are needed to identify the effects of G. fasciatus on the functioning of littoral communities and to predict and control the spread of this amphipod.     

Seasonality and trends in the Secchi disk transparency of Lake Ladoga

Data on Secchi disk transparency in Lake Ladoga, the largest lake in Europe, collected between 1905 and 2003, were used to detect climatic (interannual) trends for lake regions with various depths. The seasonal variations in Secchi depth (D _s) during the ice-free period both for limnetic regions with large differences in bathymetric characteristics and for the whole lake were estimated by more than 7000 transparency measurements. The two-dimensional data sets have a spatial resolution of approximately 20 km and are geo-referenced by latitude and longitude in Lake Ladoga. Monthly mean spatial transparency distributions and their variances were calculated from May to October. The spatial distributions of the transparency for each month are discussed within the context of lake bathymetric patterns. The maximum values of Secchi depth (more than 4 m) occur during May and October in deep regions. Both the minimum mean value of water transparency and minimum horizontal gradients of D _s for the lake occur in August. The regions with significant interannual (climatic) decreasing trends of D _s have been identified. These areas increase in summertime and cover approximately half the lake area. In spring and autumn the areas decrease and occur in the southern near-shore regions. The mean downward climatic trend of water transparency in Lake Ladoga is 0.02 m/year.     

The trophic state of Lake Ladoga as indicated by late summer phytoplankton

As a part of the joint Russian-Finnish evaluation of human impact on Lake Ladoga, we studied the phytoplankton of the lake in order to find biological indicators for eutrophication. A second aim of the investigation was intercalibration of sampling and phytoplankton counting techniques between the Russian and Finnish laboratories. Phytoplankton samples were collected from 27 sampling stations in the lake and from the rivers Volkhov and Neva in 9–13 August 1993. In surface water samples the phytoplankton fresh weight biomass varied in the range 218–3575 mg m^–33. Highest biomass values were encountered in Sortavala Bay, and lowest ones in the western central part of the lake. Phytoplankton species composition varied considerably in the lake; blue-green and green algae predominated near-shore areas and Cryptophyceae in the offshore stations. Canonical correspondance analysis revealed close grouping of eutrophy indicating communities, dominated mainly by greens and blue-greens, in the most nutrient-rich parts of Lake Ladoga, the Volkhov and Svir Bays. Samples from the vicinity of the inflows of Vuoksi and Burnaya Rivers and off Pitkaranta formed a separate group, dominated by diatoms, most of which were typical to mesotrophic or eutrophy lakes. As judged by phytoplankton biomass values and chlorophyll a concentrations, Lake Ladoga may generally be classified as mesotrophic. Eutrophicated areas are found in the northern archipelago of the lake and in the areas influenced by large rivers.     

Determinants of the parasite community of clariid fishes from Lake Victoria, Tanzania

The factors that determine parasite assemblages among the clariid fishes of Lake Victoria, Tanzania were studied between August 2003 and February 2005. Six hundred and fifty-six fish belonging to seven species were necropsied and examined for parasites, from which 31 species of metazoan parasites were recorded. The community was dominated by the nematodes both in species and numbers. Most species were generalists with only two trematodes, Diplostomum mashonense and Tylodelphys species, being specialists of Clarias gariepinus. Ten species were considered core and predictable. Parasite species richness, number of individuals per host and Shannon-Wiener diversity indices were generally high. At the compound community level, a mean number of 7.8 parasites were shared among different species of fish and the maximum number of parasites species per fish at the infracommunity level was seven. Levels of similarity in parasite species richness at the component community level ranged from 29.6 to 61.5%. The study concludes that parasite communities in clariid fishes of Lake Victoria are structured by ecological factors. At the infracommunity level, host size, diet and vagility promoted a richer parasite community. At the compound level, two factors were crucial, namely the intermixing of the waters in the lake and the predominant and mobile C. gariepinus.