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.     

Identification, phylogenetic relationships and a new maximum size of two rudd populations (Scardinius, Cyprinidae) from the Adriatic Sea drainage, Croatia

In order to determine an unknown fish population from the Vrana Lake, mitochondrial cytochrome b gene and non-coding nuclear region Cyfun P were investigated. Stabile population of Bulldog rudd, Scardinius dergle Heckel & Kner, the endemic Croatian freshwater fish in the Krka River, was genetically characterized with the same markers in order to compare it with the material from the Vrana Lake. Genetic markers were sequenced and aligned with the similar ones obtained from the GenBank in order to determine taxonomic and phylogenetic position of these two species. A significant discrepancy between nuclear genetic markers of our specimens and the sequence from the GenBank was found. Phylogenetic analysis suggested that the specimens from the Vrana Lake belong to the species S. hesperidicus. Morphometric characteristics, the maximum length and body mass showed new maximum values for both S. dergle and S. hesperidicus.     

Rudd (Scardinius erythrophthalmus) introduced to the Iberian peninsula: feeding ecology in Lake Banyoles

The first data on the ecology of rudd (Scardinius erythrophthalmus) introduced to the Iberian peninsula are presented. The habitat and diet variation of rudd were studied in Lake Banyoles (Spain), an oligotrophic karstic lake dominated by exotic fish species. Rudd were strictly littoral and the diet was based on detritus and plant material. The most important animal prey were the cladocerans Daphnia longispinaand Scapholeberis rammneri, amphipods and several late stages of nematoceran dipterans. Rudd were more zooplanktivorous in spring and autumn and less in summer. There was also a size-dependent diet shift, from microcrustaceans to macroinvertebrates. The diet of rudd was also distinguished by the importance of plant material and various small neustonic invertebrates, particularly S. rammneriand late stages of nematocerans, showing a strong resource partitioning with other fish species. The degree of herbivory in Lake Banyoles was lower than usual.     

First Finding of Ornithodiplostomum scardinii (Schulman, 1952) Sudarikov et Kurotschkin, 1968 (Trematoda,Diplostomidae) in Rybinsk Reservoir

During a parasitological survey of nonnative fish species—rudd Scardinius erythrophthalmus—in the Rybinsk Reservoir, the metacercariae Ornithodiplostomum scardinii were found in its brain. This is the first find of this helminth in the Upper Volga basin. The rudd was infected with the prevalence 31.3%, with an intensity of 1–12 parasites per fish. Data on the current distribution of the trematode O. scardinii in the Volga River basin are provided.     

Nursery habitat characteristics of an invasive,omnivorous fish

Understanding habitat use and reproductive biology of invasive species is essential to predicting invasions, designing early detection programs, and developing management plans. The rudd (Scardinius erythrophthalmus; Linnaeus, 1758) is an omnivorous fish native to Europe and western Asia that has been translocated to several countries in western Europe, New Zealand, North America, and Africa. However, little is known about early life history of rudd, particularly in invaded ecosystems, limiting our ability to predict invasions and create early detection and control programs. The upper Niagara River has the most abundant population of rudd in North America and has been the focus of several ecological investigations. Our study identified critical nursery habitats by determining which nearshore habitat factors were most strongly associated with presence of age-0 rudd. We found that emergent vegetation was the most important habitat characteristic associated with the presence of age-0 rudd. When emergent vegetation was not present, rudd were more likely to be present at sites with abundant submerged aquatic vegetation. Additionally, the odds of rudd presence decreased as distance to the nearest wetland increased. These findings can be used to create habitat-driven predictive models of rudd invasion and guide early detection programs for rudd outside their native range.

     

Feeding patterns and population structure of an invasive cyprinid,the rudd <Emphasis Type="Italic">Scardinius erythrophthalmu</Emphasis>s (Cypriniformes,Cyprinidae), in Buffalo Harbor (Lake Erie) and the upper Niagara River

Feeding patterns and population structure of the non-native rudd Scardinius erythrophthalmus (Linnaeus) were examined to understand their ecology in Buffalo Harbor and the Niagara River. We hypothesized that (1) the diet of rudds would be omnivorous, but contain greater proportions of macrophytes in summer months, (2) feeding intensity would increase with water temperature, and (3) condition and growth would be similar to other populations. We collected rudds with a variety of gears in 2009 to test these hypotheses, and used data from 2007 to 2010 seining surveys to determine if the relative abundance of young-of-the-year rudd differed among sites with different flow conditions. Rudds were mostly herbivorous; they consumed aquatic macrophytes in summer and supplemented their diet with algae and fish in spring and fall. Feeding intensity was positively correlated with water temperature, but significantly reduced during spawning. Rudd condition and growth were greater than estimates from other populations, suggesting increases in abundance and range expansion are possible. Furthermore, reproduction was successful at lotic sites but very poor at sites without measureable flow, contrary to the paradigm of optimal rudd habitat. Research is needed to understand how herbivory by abundant rudd populations affects native aquatic communities.     

Implications of rudd (Scardinius erythrophthalmus) herbivory on submerged macrophytes in a shallow eutrophic lake

The role of rudd (Scardinius erythrophthalmus) herbivory was studied in Kirkkojärvi, a shallow and turbid basin in Lake Hiidenvesi, Finland. The submerged species dominating in the rudd diets were Potamogeton obtusifolius, Ranunculus circinatus, Sparganium emersum, bryophytes, and filamentous algae. Plant consumption estimated with bioenergetics modelling increased with fish age, being highest in late summer concomitant with the macrophyte biomass peak. Depending on the age structure, a rudd biomass of 20 kg ha^?1 consumes 18–23 kg of macrophytes ha^?1 a^?1, while a rudd biomass of 100 kg ha^?1 results in plant consumption of 92–115 kg ha^?1 a^?1. Although, rudd seemed to feed rather unselectively on suitable-sized and edible plants, some species abundant in the littoral, such as Myriophyllum verticillatum and pleustophytic Ceratophyllum demersum, were not found in rudd guts, indicating selective plant consumption. In Kirkkojärvi, selective grazing by rudd and increased turbidity and high nutrient levels partly caused by bottom dwelling cyprinid fish, may promote the inedible and pleustophytic macrophytes, which have increased in Kirkkojärvi during the past decades.

     

Short-term and long-term effects of zooplanktivorous fish removal in a shallow lake: a synthesis of 15 years of data from Lake Zwemlust

SUMMARY 1. Removal of zooplanktivorous fish (mainly bream) in 1987 from a shallow eutrophic lake in the Netherlands, Lake Zwemlust, resulted in a quick switch from a turbid state with cyanobacteria blooms to a clear state dominated by macrophytes.
2. The clear state was not stable in the long term, however, because of high nutrient loadings.
3. In 1999, another removal of zooplanktivorous fish (mainly rudd) had similar effects as in 1987, although macrophytes returned more slowly.
4. In the years directly following both interventions there was a 'transition period' of very clear water with high densities of zooplanktonic grazers in the absence of macrophytes; low oxygen concentrations indicate that during those years primary production was low relative to heterotrophic activity.
5. The transition period appears to provide the light climate necessary for the return of macrophytes.
6. Reduction of nutrient loading is necessary to improve water quality in Lake Zwemlust in the long term. In the short term, repeated fish stock reduction is a reasonable management strategy to keep Lake Zwemlust clear.     

Population genetics of the freshwater mussel, <Emphasis Type="Italic">Amblema plicata</Emphasis> (Say 1817) (Bivalvia: Unionidae): Evidence of high dispersal and post-glacial colonization

Over 70% of North American freshwater mussel species (families Unionidae and Margaritiferidae) are listed as threatened or endangered. Knowledge of the genetic structure of target species is essential for the development of effective conservation plans. Because Ambelma plicata is a common species, its population genetic structure is likely to be relatively intact, making it a logical model species for investigations of freshwater mussel population genetics. Using mtDNA and allozymes, we determined the genotypes of 170+ individuals in each of three distinct drainages: Lake Erie, Ohio River, and the Lower Mississippi River. Overall, within-population variation increased significantly from north to south, with unique haplotypes and allele frequencies in the Kiamichi River (Lower Mississippi River drainage). Genetic diversity was relatively low in the Strawberry River (Lower Mississippi River drainage), and in the Lake Erie drainage. We calculated significant among-population structure using both molecular markers (A.p. Φ_st = 0.15, θ_st = 0.12). Using a hierarchical approach, we found low genetic structure among rivers and drainages separated by large geographic distances, indicating high effective population size and/or highly vagile fish hosts for this species. Genetic structure in the Lake Erie drainage was similar to that in the Ohio River, and indicates that northern populations were founded from at least two glacial refugia following the Pleistocene. Conservation of genetic diversity in Amblema plicata and other mussel species with similar genetic structure should focus on protection of a number of individual populations, especially those in southern rivers.     

Health status of rudd (Scardinius erythrophthalmus hesperidicus H.) in Lake Vrana on the Island of Cres, Croatia

The health status of rudd ( Scardinius erythrophthalmus hesperidicus H.) in Lake Vrana, the largest Croatian karstic lake, was evaluated. Studies comprising parasitological, haematological and bacteriological surveys were conducted over a 2-year period. Parasitological examination revealed a light infestation of 27% of the examined fish, mostly Dactylogyrus and Ichthyophthirius species. Haematological studies showed that haematocrit values were lower than the physiological limit. A haematocrit coefficient of correlation in all research periods was higher than 15%, indicating that the majority of fish in the study were susceptible to the development of bacterial and other diseases. Indeed, a diverse array of bacteria were isolated from rudd, mainly Flavobacterium spp. and Aeromonas spp., but also some specific fish pathogens, notably Pasteurella piscicida, Yersinia ruckeri , and Edwardsiella ictaluri , were identified. Under stress conditions, detected bacterial species can give rise to disease outbreaks.     

A re‐examination of the molecular phylogeny and biogeography of the genus Schizothorax (Teleostei: Cyprinidae) through enhanced sampling,with emphasis on the species in the Yunnan–Guizhou Plateau,China

The mitochondrial DNA cytochrome b sequences of 36 Schizothorax species from 51 localities in the Yunnan–Guizhou Plateau (YGP) and its adjacent areas were analysed. Maximum parsimony, Maximum likelihood and Bayesian phylogenetic analyses were performed to examine the relationships of Schizothorax species. A hypothesis of the phylogenetic relationships of the species is given. A relaxed molecular clock based on Bayesian evolutionary analysis was used to tentatively calculate the divergence times of Schizothorax. Samples from the YGP were tentatively grouped into three geographically distributed clades: the Tsangpo‐Irrawaddy, the Mekong‐Salween and the Trans‐Jinsha River (including Jinsha, Red, Nanpan and Beipan Rivers). Calibration of the molecular clock revealed that two geological periods, the late Miocene about 10 million years before present (Myr BP) and the Pliocene (4.0 Myr BP), were important times in the vicariant speciation of Schizothorax. The phylogenetic history of the species is congruent with events caused by the uplift of the Tibetan Plateau and the YGP. The divergence of Schizothorax species in YGP began in the Pliocene. Our phylogenetic trees did not support the hypothesis that the paleo Jinsha River was drained through the Yangtze River‐Jianchuan Lake‐Erhai Lake to the Red River. Schizothorax in the Beipan River were derived from the Jinsha River.     

Photosynthetic pigments of plankton in some karst lakes of central Russia

Phytoplankton pigments were studied in seven soft water, weakly mineralized karst lakes in central Russia (Vladimir oblast). The lakes Kshchara, Sankhar, Yukhor, Bol’shoye Poridovo, Svetlen’koye, Bol’shie, and Malye Garavy were investigated. The seasonal dynamics, vertical distribution of chlorophyll a, and its content in the phytoplankton biomass were considered. The relationship between chlorophyll a content and abiotic factors was analyzed. In addition to algae pigments, high concentrations of bacterial chlorophyll d were recorded in meta- and hypolimnetic layers of lakes Yukhor, Kshchara, Sankhar, and Svetlen’koye.     

A reintroduced lake sturgeon population comes of age: A genetic evaluation of stocking success in the St. Louis River

Lake sturgeon (Acipenser fulvescens) have experienced significant declines throughout the Great Lakes, leading to stocking efforts at some locations to reestablish extirpated populations. Given the late sexual maturity of the species, assessment of stocking program success is often delayed. Lake sturgeon were extirpated from the St. Louis River in western Lake Superior. Stocking began in 1983 and continued until 1994, using the Wolf River (Lake Winnebago) in the Lake Michigan basin as the source. Stocking resumed from 1998 to 2000, using the Sturgeon River in Lake Superior as the source. Our objectives were to (a) determine the movement patterns of stocked Wolf River sturgeon, (b) determine whether stocked individuals are migrating into natural spawning populations during the spawning season, (c) identify the origins of individuals captured in the St. Louis River, and (d) assess the genetic diversity of the reintroduced St. Louis River population. All collected samples were analyzed using 12 microsatellite loci, followed by genetic assignment testing to achieve the first three objectives. Genetic diversity was compared to natural spawning populations in Lake Superior. The highest proportion of stocked Wolf River lake sturgeon was detected in western Lake Superior, close to the stocking site. However, individuals were detected throughout Lake Superior. Wolf River individuals were detected in most of the spawning populations in Lake Superior, with the greatest number in the Sturgeon River and the Goulais River. The majority of individuals captured in the St. Louis River were of stocked origin (88.1%), with 73.5% from the Wolf River and 14.6% from the Sturgeon River. These observed proportions differed from the expected proportions based on the number of sturgeon released from each source (χ² = 55.37, p < 0.00001), with a higher representation of Sturgeon River individuals. Evidence of natural recolonization in the St. Louis River was detected from Lake Huron and Goulais River individuals. Genetic diversity of the St. Louis River population was comparable to levels observed in the remnant natural populations in Lake Superior. However, the effective population size of the St. Louis River was small (N_e = 38.1) and average relatedness among individuals was relatively high (r = 0.151). Monitoring of movement of stocked Wolf River sturgeon throughout Lake Superior should continue, with careful attention to the potential for outbreeding depression in remnant populations. Genetic diversity of the St. Louis River population should also continue to be monitored to see if it improves with increased natural reproduction.     

Sedimentary diatom assemblages in the northern part of Lake Tanganyika

Surface sediment diatoms from the northern part of Lake Tanganyika were analysed with several ordination and classification techniques. Three sample groups characterized by four diatom assemblages were recognized. The first sample group occurs in a rather shallow area near the delta of the Rusizi River on a coarse-grained sand substrate. The second and most important sample group occurs on the silty bottom of an underwater depression situated off the delta of the Rusizi River in the north-eastern part of Lake Tanganyika; its diatom composition has a great affinity to the Rusizi River diatom population. The third sample group contains all the other samples and covers an area corresponding to the west-, east- and southward continuation of the area of the second group: its diatom composition is also related to the Rusizi River diatom population, but in a less pronounced manner.     

Special traits of growth and feeding of the stone sculpin <Emphasis Type="Italic">Paracottus knerii</Emphasis> (Cottidae) in water bodies of different types

Growth and feeding of the stone sculpin Paracottus knerii (Cottidae) is investigated in Water Bodies of Different Types: Baikal (the littoral of its southern part), the Angara River, and the mountainous Sobolinoe Lake (the southern Baikal basin). The highest growth rate is characteristic of the South-Baikalian population, followed by the Angara population. The stone sculpin from Sobolinoe Lake is slow-growing. The growth rate of specimens of the latter is by 1.5–2 times lower than in the two aforementioned populations due to inferior feeding conditions of this water body. The size-age changes in the food spectrum of all investigated populations are consecutive change of all principal components and increase in size of the consumed prey     

Effects of contrasting omnivorous fish on submerged macrophyte biomass in temperate lakes: a mesocosm experiment

1. Freshwater fish can affect aquatic vegetation directly by consuming macrophytes or indirectly by changing water quality. However, most fish in the temperate climate zone have an omnivorous diet. The impact of fish as aquatic herbivores in temperate climates therefore remains unclear and depends on their dietary flexibility. 2. We tested the effects of a flexible omnivore and an herbivore on aquatic vegetation by comparing the effects of rudd (Scardinius erythrophthalmus, the most herbivorous fish in temperate climates) with grass carp (Ctenopharyngodon idella) in a mesocosm pond study. Exclosures distinguished herbivorous effects of fish on submerged macrophytes from indirect effects through changes in water quality, whereas stable isotope food‐web analysis provided information on fish diets. 3. We hypothesised that rudd, with its flexible diet and preference for animal food items, would only indirectly affect macrophytes, whereas grass carp, with its inflexible herbivorous diet, would directly affect macrophyte biomass. 4. Only grass carp significantly reduced macrophyte biomass through consumption. Rudd had no effect. Food‐web analysis indicated that rudd predominantly consumed animal prey, whereas grass carp included more plants in their diet, although they also consumed animal prey. Grass carp significantly affected water quality, resulting in lowered pH and increased N‐NH₄ concentrations, whereas more periphyton growth was observed in the presence of rudd. However, the indirect non‐herbivorous effects of both fish species had no effect on macrophyte biomass. 5. Both fish species should be considered as omnivores. Despite the fact that rudd is the most herbivorous fish in the western European climate zone, its effect on submerged macrophyte biomass is not substantial at natural densities and current temperatures.     

Late- and postglacial history of lakes of the Karelian Isthmus

The Late Pleistocene and Holocene history of five lakes in the central part of Karelian Isthmus, south of the present Vuoksi River, are described on the basis of sediment stratigraphical investigations. Two of the Lakes, Michurinskoe (94 m a.s.l.) and Uzornoe (55 m a.s.l.) are situated in an upland area that remained dry land after the deglaciation even during the early high water stages of the Baltic Sea (Baltic Ice Lake until c. 10 000 yr BP and Ancylus Lake 9500–8800 BP). The low-lying central parts of the Isthmus were flooded by the outflow of Lake Ladoga that took place across this area until the formation of Neva River, c. 3 100 yr BP, and further by the waters of River Vuoksi that started flowing into the area from the NW c. 5000 yr BP as a new outlet of Lake Saimaa. The basins of the lakes Krasnoe and Vishnevskoe (both 16 m a.s.l.) became isolated when River Neva was formed and Lake Ladoga sank to its present level. Lake Rakovoe (12 m a.s.l.) was on the level of River Vuoksi up until the mid-19th century, when water level in the central stretch of the river was artificially lowered. Each of the lakes has been variously affected by hydrological and climatic changes and consequences of human activities, e.g. eutrophication due to intensified land use. As a consequence to artificial lowering, done in order to gain field and meadowland, the large, shallow Lake Rakovoe has been largely overgrown by macrophytic vegetation.     

Genetic characterization and management of the endangered Mohave tui chub

The Mohave tui chub (Siphateles bicolor mohavensis) is the only fish native to the Mojave River, California. The fish were displaced by introduced arroyo chubs (Gila orcutti) throughout most of their range, starting in the 1930s. Two potentially relictual populations and two transplanted populations were genetically characterized using 12 microsatellite DNA loci, along with contemporary cyprinid populations in the Mojave River. We found only un-hybridized Mohave tui chubs in the refuge populations, and only un-hybridized arroyo chubs in the Mojave River. The two largest Mohave tui chub populations (Lake Tuendae and China Lake) exhibit similar, comparatively high genetic variation. Another large population (Camp Cady) with low genetic diversity shows the effect of a bottleneck of ten individuals during the historic founding event. The fourth population (MC Spring) has the fewest alleles, lowest heterozygosity, and is the most divergent, suggesting that genetic drift from a persistently low effective population size has reduced genetic diversity since its apparent isolation in 1934. We recommend instituting artificial gene flow to rebuild genetic variation in Camp Cady from both Lake Tuendae and China Lake, and the establishment of new populations with founders from both Lake Tuendae and China Lake. Additionally, we comment on the infeasibility of restoring populations of Mohave tui chub in their historic habitats.     

State of the reproductive system of Cyprinidae from the Teterev River and Kiev Reservoir after the Chernobyl accident

The state of the reproductive system in four species of Cyprinidae from the Teterev River and Kiev Reservoir (Ukraine)—descendants of F₃–F₆ generations of individuals subjected to the radiation impact because of accident at the Chernobyl Nuclear Power Plant—has been studied. It was shown that 20 years after the accident, there is a wide range of morphofunctional anomalies of this system in fish. The most significant of them are asymmetry and abnormal morphology of gonads; proliferation of connective tissue-sterilization; and mass destruction of sexual cells of different stages of development. Disturbances of reproductive gonads among the studied species are expressed most strongly in bream Abramis brama and rudd Scardinius erythrophthalmus. In the series of studied generations, maximum frequency of occurrence of gonad anomalies in bream and silver bream Blicca bjoerkna was recorded in F₃–F₄ and that in roach Rutilus rutilus and rudd was recorded in F₄–F₅, which is determined by the phenomenon of prolonged mutagenesis.     

Invasive species alter ontogenetic shifts in the trophic ecology of Lake Sturgeon (<Emphasis Type="Italic">Acipenser fulvescens</Emphasis>) in the Niagara River and Lake Ontario

Species invasions can alter food web structure and change ecosystem-level functioning, but it is often unclear how these invasions may affect the life history of native species. The Lake Sturgeon (Acipenser fulvescens), a large long-lived native fish species in the Great Lakes, has increased in abundance in the lower Niagara River and nearby Lake Ontario during a period of invasive species-induced ecosystem change precipitated most recently by Dreissenid mussels (Driessena polymorpha and Driessena bugensis) and Round Goby (Neogobius melanostomus). Material taken from cross-sections of archived pectoral spines from Niagara River Lake Sturgeon captured in 1998–2000 and 2010–2012 were analyzed for stable isotopes across discrete growth zones to provide an ontogenetic assessment of diet, and diet analysis of Lake Sturgeon captured in 2014 was conducted to assess the contribution of invasive prey. Round Goby was the most important Lake Sturgeon prey item (86% by weight) in 2014, which corroborated results of δ¹⁵N and δ¹³C. Lake Sturgeon captured after the invasion of Round Goby exhibited ontogenetic changes in δ¹⁵N that differed from pre-Round Goby patterns, though this effect was weaker for δ¹³C. Values of δ¹⁵N from spine growth zones indicated non-linear increases in trophic position with age and increased rate of δ¹⁵N enrichment after the Round Goby invasion. We conclude that Round Goby establishment in western Lake Ontario changed the feeding ecology of Lake Sturgeon, which may have a positive effect on population growth for this native species.