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Dynamics of coastal fish assemblages in the Baltic Sea are still rather poorly understood. In particular, little information is available on migrations and movements of the small-bodied littoral fish species like Eurasian minnow ( Phoxinus phoxinus L.). Minnow is considered typically as a river and lake species, but it also inhabits brackish coastal waters of the Baltic Sea. In this study, we investigated movement patterns of brackish water inhabiting minnows using otolith microchemistry. Fish were collected from four different sites (from two bays and two stream mouths) around Saaremaa Island. The results indicated that at least three distinct migration patterns exist: (i) seawater residency, (ii) fast springtime migrations to fresh water or to bays with lower salinities (areas near stream mouths) and (iii) prolonged migrations to fresh water (some cases overwintering in streams). Migration patterns listed above were not evenly distributed among sites, and some individuals did not migrate to fresh water in every year. None of the analysed fish were freshwater residents. Additionally, potentially ontogenetic effects on Mn and Sr concentrations were observed in the otolith core regions, which may have important implications for the interpretation of otolith chemistry data. The overall findings of this study demonstrate that much more complex migration patterns exists in brackish water inhabiting minnow populations than previously thought and at least some individuals do enter freshwater to reproduce. [ABSTRACT FROM AUTHOR]

Sexual segregation, where males and females use habitat in different ways, is widespread among animals including fish, and has important consequences for key aspects of population ecology including foraging success, predator avoidance and growth. However, currently, evidence for sexual segregation is based on observations of sexually dimorphic species or species with differing reproductive strategies. We used European minnows, Phoxinus phoxinus, to test the null hypothesis that sexual segregation does not occur in sexually monomorphic species. A large, seminatural stream channel equipped with passive integrated transponder (PIT) detectors monitored the activity of 70 fish for 98 days on ecologically relevant spatial and temporal scales. Sexual segregation was evident spatially (with males and females using different habitats within the stream), temporally (males switched patches more frequently than females at night, but not during the day) and socially (with males, but not females, demonstrating same-sex association preferences). Our results are the first to demonstrate sexual segregation in monomorphic species outside the breeding season. We discuss potential explanations for our observations and ways in which patterns of variation in activity, space use and social interactions have important implications for population dynamics. [ABSTRACT FROM AUTHOR]

Despite that the existence of animal personalities is widely recognized, no consensus has been reached on the relative importance of different ecological factors behind their expression. Recently, it has been suggested that parasites may have a crucial role in shaping animal personalities, but only a very few studies have experimentally tested the idea. We infected Eurasian minnows ( Phoxinus phoxinus) with the brain-encysted trematode parasite, Diplostomum phoxini, and studied whether infection could modify the personality of their hosts. Our results show that D. phoxini infection did not affect the mean levels of boldness, activity or exploration, but infected minnows showed higher repeatability in boldness and activity, and reduced repeatability in exploration. We also found that D. phoxini may be able to break the associations (behavioral syndromes) between behavioral traits, but that this effect may be dependent on parasite intensity. Furthermore, the effect of D. phoxini infection on personality of the hosts was found to be nonlinearly dependent on infection intensity. Taken together, our results suggest that D. phoxini parasites may shape the personality of their hosts, but that behavioral consequences of ecologically relevant infection levels may be rather subtle and easily remain undetected if only the mean trait expressions are compared. [ABSTRACT FROM AUTHOR]

The association between male secondary sexual ornamentation and male quality has been under intensive study for decades. It has been shown that male ornaments in fish indicate a variety of physical and genetic qualities. However, only few studies have investigated whether male ornaments signal locomotor performance, a trait that is expected to be vital for individual fitness in the nature. In this study, we sampled two populations of European minnow ( Phoxinus phoxinus), a cyprinid fish species with spectacular and colourful male breeding ornamentation, and examined the association between male ornaments (tubercle number, lateral darkness and abdominal redness), swimming performance, and three fitness-related traits, body length ( LT), condition factor ( K) and gonadosomatic index ( GI). We found that male tubercle number and abdominal redness were positively correlated with their swimming performance. In addition, these two ornaments were correlated with male fitness-related traits, which in turn were also directly associated with the swimming performance. In general, these results suggest that in the European minnow male ornamentation may act as an honest signal of several fitness-related traits and locomotor performance in the nature. [ABSTRACT FROM AUTHOR]

Non-invasive diagnoses for most of the extraintestinal helminth infections among vertebrates are rare. In the present study, we developed and tested a non-invasive visual diagnosis method to detect the infection of the nematode Philometra ovata, which is parasitising in the body cavity of the common minnow Phoxinus phoxinus. By observing the surface of minnow's abdomen, we diagnosed infected minnows with irregular or vermiform-shaped uplifts as a consequence of the presence of P. ovata in the body cavity. We conducted the diagnosis in minnows with or without anaesthetisation, and our results showed the non-invasive method is highly reliable (correct rate of diagnoses > 95 %) in both anaesthetised and non-anaesthetised groups. The correct rate of diagnoses in truly uninfected fish (i.e. specificity) was nearly 100 % in both groups, while the correct rate of diagnoses in truly infected fish (i.e. sensitivity) was 71 and 65 % in anaesthetised and non-anaesthetised fish, respectively. The correct rate in fish diagnosed as infected or uninfected (i.e. positive or negative predictive power) of non-invasive diagnosis was nearly 100 % among the anaesthetised fish, and over 95 % in non-anaesthetised group. The diagnosis also yielded prevalence of P. ovata infection similar to the real prevalence in anaesthetised fish. Diagnoses conducted by an inexperienced observer indicated that the method is repeatable. Taken together, the present non-invasive method seems to be a promising new tool for non-invasive detection of P. ovata infections in minnows and probably can be applied for the detection of other body cavity dwelling metazoan parasites in various host taxa. [ABSTRACT FROM AUTHOR]

A molecular analysis examining the level of relatedness in shoaling minnows Phoxinus phoxinus was conducted. The results revealed that individuals from within the same shoal were not more closely related to each other than to individuals from other shoals. This led to the conclusion that Schreckstoff may be less likely to have evolved in the context of kin selection. [ABSTRACT FROM AUTHOR]

Natural selection drives local adaptation, potentially even at small temporal and spatial scales. As a result, adaptive genetic and phenotypic divergence can occur among populations living in different habitats. We investigated patterns of differentiation between contrasting lake and stream habitats in the cyprinid fish European minnow ( Phoxinus phoxinus) at both the morphological and genomic levels using geometric morphometrics and AFLP markers, respectively. We also used a spatial correlative approach to identify AFLP loci associated with environmental variables representing potential selective forces responsible for adaptation to divergent habitats. Our results identified different morphologies between lakes and streams, with lake fish presenting a deeper body and caudal peduncle compared to stream fish. Body shape variation conformed to a priori predictions concerning biomechanics and swimming performance in lakes vs. streams. Moreover, morphological differentiation was found to be associated with several environmental variables, which could impose selection on body and caudal peduncle shape. We found adaptive genetic divergence between these contrasting habitats in the form of 'outlier' loci (2.9%) whose genetic divergence exceeded neutral expectations. We also detected additional loci (6.6%) not associated with habitat type (lake vs. stream), but contributing to genetic divergence between populations. Specific environmental variables related to trophic dynamics, landscape topography and geography were associated with several neutral and outlier loci. These results provide new insights into the morphological divergence and genetic basis of adaptation to differentiated habitats. [ABSTRACT FROM AUTHOR]

Sexual displays often involve many different signal components, which may give information about the same or different mate qualities. We studied the information content of different signals in male minnows (Phoxinus phoxinus) and tested whether females are able to discriminate between males when only olfactory cues are present. We found that females preferred the odour of males with a more saturated (i.e., redder) belly, but only when the females had been in physical contact with the males before the experiments. Instead, when unfamiliar males were used, females did not discriminate between male odours and also the overall swimming activity (mate choice intensity) of the females was significantly lower. More ornamented males had lower number of Philometra ovata parasites (indicated by belly saturation) and Neoechinorhynchus rutili parasites (indicated by belly hue) than their less ornamented counterparts. We did not find experimental evidence for female odour preference being linked to belly hue and breeding tubercle number, but in the nature these traits were associated with the condition factor of the males. Taken together, our results suggest that belly colouration and breeding tubercles give honest information on several aspects of male quality. In addition females may learn the association between male colouration and their olfactory signals and utilize this information when visual signals are not present. [ABSTRACT FROM AUTHOR]

Studies of the brown trout ( Salmo trutta) population in the Norwegian subalpine lake, Øvre Heimdalsvatn, over a 50-year period have revealed major changes in population dynamics. In 1958, the population density was high, with individuals stagnating in growth at lengths below 30 cm. After heavy exploitation during the years 1958–1969, the number of older fish declined substantially, and growth rates increased significantly. Since 1969, the European minnow ( Phoxinus phoxinus) have been observed in the lake, with increasing densities from 1977–1978 to 1999–2000. The age structure of the brown trout population has changed markedly from the 1960s to the period 1993–2006. Annual recruitment significantly declined, from an average number of 3746 individuals in age-class 4 during the period 1958–1966 to an average of 1668 during the period 1993–2006. However, due to lower exploitation rates, the number of old fish was significantly higher in the latter period. The summer diet of brown trout has changed substantially from a dominance of the large crustaceans Lepidurus arcticus and Gammarus lacustris to a high occurrence of European minnows, while L. arcticus has become practically absent from the diet. There was a negative relationship between brown trout biomass and annual length increment. However, despite a brown trout biomass at the same level during the years 1993–2006 as in the 1960s, annual individual growth rates have significantly declined. The reduced recruitment and reduced annual growth rates of the brown trout, as well as changes in the diet, are most likely related to the introduction and establishment of the invasive species, the European minnow. [ABSTRACT FROM AUTHOR]

A study of the diet of native brown trout ( Salmo trutta) parr and introduced European minnow ( Phoxinus phoxinus) in the subalpine lake, Øvre Heimdalsvatn, showed that the two species had considerable dietary overlap, both in the littoral zone and in the outlet of the lake. Chironomidae constituted a substantial proportion of the diet of the two species in both habitats. The results indicated that both zooplankton (Cladocera) and large macroinvertebrates (EPT-species) made up a higher proportion of the minnow diet in the early phase of the minnow establishment (1975–1977) than later, and that the significance of small macroinvertebrates (Chironomidae) as prey has increased during the same period. Dietary analysis of the sympatric brown trout and minnow population in Øvre Heimdalsvatn does not provide a definitive conclusion about the degree of competition between the two species. However, together with the findings in other studies in Øvre Heimdalsvatn that have documented reduced recruitment and individual growth of brown trout, decreased individual growth of minnows and a marked decline in the density of large crustaceans ( Lepidurus arcticus and Gammarus lacustris) in the shallow littoral of the lake during the last decades indicates that competitive interactions between the two species are likely. This is probably an example of the competition between two fish species with a high degree of dietary overlap when living in sympatry, most likely caused by absence of alternative prey and alternative habitats due to the high predation risk for both brown trout parr and minnows in deeper parts and in the open waters of the lake. [ABSTRACT FROM AUTHOR]

The littoral benthos of the subalpine lake, Øvre Heimdalsvatn, has been documented in a series of investigations carried out in 1972, 1976, 1985 and 2000. During this 28-year period there have been major changes in the benthos of the lake following the introduction of European minnow ( Phoxinus phoxinus) into the lake where brown trout ( Salmo trutta) was formerly the sole species. In 1972 Ephemeroptera, Trichoptera, Plecoptera and Gammarus lacustris dominated the macrobenthos, constituting 85% of faunal numbers, while Chironomidae and Oligochaeta made up only c. 6%. However, by 1976, chironomids and oligochaetes had increased in relative abundance, while G. lacustris declined. This trend towards a dominance of chironomids and oligochaetes was confirmed in 1985 and 2000, although absolute numbers of Ephemeroptera, Plecoptera and Trichoptera increased in 2000 relative to 1972 values. Gammarus lacustris had a 2-year life cycle in Øvre Heimdalsvatn. In 1972 there were significantly more females than males, but by 1976 and through to 2000 there were greater numbers of males. Despite this reduction in females, numbers of juveniles increased, although mortality, probably due to increased predation from minnows, was higher than earlier. The introduction of the alien species, the European minnow, into Øvre Heimdalsvatn has clearly changed the composition and structure of the littoral macroinvertebrate benthos. [ABSTRACT FROM AUTHOR]

Data from the International Biological Programme (IBP) and subsequent studies have been re-analysed to test the two hypotheses which previously have been suggested concerning the zooplankton in the mountain lake, Øvre Heimdalsvatn: (1) the average temperature in June, more than other summer months, is affecting the growth rate and population densities of zooplankton in the lake, (2) the invasion of the European minnow ( Phoxinus phoxinus) has caused changes in the zooplankton community. The analyses have demonstrated that the June temperature strongly affects the growth rate of all the zooplankton species, but that there is no relationship with the population maxima. The species composition in the crustacean zooplankton has not changed between 1969 and 1999, and any direct impact of the minnows on the zooplankton community could not be detected. Indirectly, the minnows may have reduced the density of invertebrate predators, and thus caused an increase in juvenile survival and increased summer maximum density of Bosmina longispina. The variation in density of the copepod, Cyclops scutifer, was correlated with the density of Heterocope saliens, most likely the result of predator–prey interactions. [ABSTRACT FROM AUTHOR]

The alien fish species, European minnow ( Phoxinus phoxinus), was recorded in the mountain lake, Øvre Heimdalsvatn, southern Norway, for the first time in 1969. After some years minnows were observed in the diet of brown trout ( Salmo trutta). In 2006, brown trout had significantly higher δ15N values than European minnow, indicating that brown trout holds the top trophic position in the lake food web. The δ15N signatures of brown trout were significantly correlated to fish size, age and mercury concentration, while δ15N signatures in minnows did not show any change with fish size, age and mercury concentrations, indicating that European minnow remain at the same trophic level throughout the life history. The mercury concentrations (mg kg−1 w.w.) in brown trout and minnows were in the range 0.014–0.093 and 0.014–0.16, respectively. For both species, positive relationships between total mercury concentrations and fish length, weight and age were found. Although European minnow was found as prey in brown trout stomachs, minnow had significantly higher mercury concentrations than brown trout. It is most likely that the higher mercury concentrations in the European minnow are due to the high metabolic rate, with more energy spent on maintenance than on growth as a consequence of its small size and very low annual growth rate compared to brown trout. Changes in population densities of both brown trout and European minnow may influence their habitat use, feeding preferences and metabolism, and may thus potentially lead to changes in the mercury loads of both species. [ABSTRACT FROM AUTHOR]

The article provides an overview of a study which examines the immune response to nematode larvae in the liver and pancreas of minnow, Phoxinus phoxinus. It provided data which describing the ultrastructure of the rodlet cells (RC), mast cells (MC), neutrophils, macrophages and fibers infected of liver and pancreas of minnow, as well as the relationship between the cells and nematode larvae. It also provided further evidence on the significant role of the piscine inflammatory network as a response to endohelminth infection.

Hamilton''s theory of the selfish herd suggests that gregarious behaviour is a strategy by which individuals seek cover behind other group members to reduce the risk of predation. Therefore, it can be predicted that individuals will have less reason to seek cover within a group if the habitat itself provides physical structure, and therefore cover. We tested this prediction with European minnows, Phoxinus phoxinus, in a large, seminatural stream channel using a fully factorial design in which habitat complexity and predation risk were manipulated independently. We recorded shoal size, rates of movement and association preferences for familiar fish. Consistent with predictions, European minnows responded to the presence of predatory pike, Esox lucius, by forming larger shoals, but this effect was observed only in structurally simple habitats. Fish also responded to increased predation risk by reducing their rates of movement, and this was particularly pronounced in complex habitats. Association preferences for familiar fish were unaffected by predation risk in simple habitats. Together, these results suggest that when at risk from predation, European minnows shoal to obtain shelter, but only when there is insufficient physical structure available. Moreover, the results show the extent to which physical habitat complexity can affect the expression of gregarious behaviour. [Copyright &y& Elsevier]

Replicated, naturalistic mesocosms were used to investigate whether pre-existing preferences for familiar individuals decay when opportunities to form new alliances arise. In each trial, two groups of wild European minnows Phoxinus phoxinus were introduced to a common environment, and their association patterns monitored continuously over a 3 week period using passive integrated transponder (PIT) tags. Individuals within a group were familiar, but had no previous experience of the other group. European minnows associated initially with previously familiar individuals more frequently than expected by chance. This preference then diminished over a period of 2 weeks following their encounter with the unfamiliar group of fish and was not detectable by the third week. Instead, new association patterns resulting from non-random re-assortment of individuals over time were evident. The results show that new alliances between individuals form when wild shoals coalesce. [ABSTRACT FROM AUTHOR]

Little is known about how food location ability of animals is affected by social information of predation risk. This question was therefore addressed in an experimental study where naïve ‘observer’ European minnows ( Phoxinus phoxinus) were allowed to search for food in a maze in the presence or absence of a predator ( Salmo trutta). Observer minnows were accompanied by conspecific demonstrators which had previously been trained in the same maze either in the presence or absence of the predator. Observer minnows were most likely to locate food when the predator was absent both during their trial and during the pre-training of demonstrators. When demonstrators had been trained with predators, observer success in locating the food was halved, although they were never exposed to predation risk themselves. When observers were exposed to predation risk their probability of locating food was further reduced regardless of the experience of their demonstrators. Our results show that predation risk can affect the foraging ability of minnows both directly and indirectly through social information from conspecifics. We conclude that social information may influence and constrain individual behavioural decisions, especially in rapidly changing environments where private information is often insufficient. [ABSTRACT FROM AUTHOR]

The mechanisms and functions of mixed-species shoaling were investigated in two sympatric species of cyprinids, the chub and the European minnow, from the river Wharfe where they comprised approximately 70% of all year 0+ fish over a 20-year survey. Chub preferred conspecific shoals over heterospecific ones with olfactory cues being more important than visual ones for shoal choice. This preference was consistent with measurements of length:flank area ratios and length:weight ratios which suggest that both species are similar in appearance. When presented with mixed-species shoals, chub increased the percentage time spent with stimulus shoals with increasing proportions of conspecifics. Feeding experiments suggest that the preference for conspecific shoals is driven by interspecific competition (with minnows out-competing similar-sized chub) and the oddity effect. The importance of this work in the context of species assortment in free-ranging shoals is discussed. [ABSTRACT FROM AUTHOR]

Minnows Phoxinus phoxinus, studied 30 years after the first record of the species in the subalpine Lake Øvre Heimdalsvatn, Norway, ≥55 mm LT, were estimated to have densities ofc . 4·7 kg ha−1 (120 000 fish) in June 1999 and 2·1 kg ha−1 (63 000 fish) in June 2000. The population was characterized by low individual growth, delayed age of maturity and lived longer when compared to values reported in a previous study in the early phase of its establishment, and other values reported in the literature. Most minnows reached sexual maturity at 4–5 years and >55 mm LT. Although the estimated annual survival of minnows >55 mm was low (S=0·2), ages up to 13 years were recorded. Despite a moderate increase in the population size during the last 20 years, the present reduction in individual growth, followed by delayed age of maturity, suggested the existence of density-dependent effects on the population dynamics of the minnows. The minnows were restricted to the littoral zone and near bottom areas. A vertical or horizontal expansion in habitat use was probably prevented by the presence of piscivorous brown trout Salmo trutta. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Minnows Phoxinus phoxinus did not show any difference in the average distance from a predator associated with the left or right position of a shoal-mate. While inspection behaviour of fish tested with a mirror on their left side was indistinguishable from the behaviour of controls tested without a mirror, inspection behaviour of fish tested with the mirror on their right side appeared to be changed and incoherent in both temporal and spatial parameters. These results suggest that, as in mosquitofish Gambusia holbrooki, the condition with the mirror on the left provided the best arrangement of monocular lateral stimulation in which each stimulus fell into the correct lateral visual field. Minnows showed a significant left eye preference during scrutiny of their mirror image when tested in the absence of any predator and a significant right eye preference while monitoring a live predator in the absence of a social partner. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Summary 1. For animals that have access to a predator-free refuge, the daily timing of feeding activity should reflect temporal variation in both the risk of predation while foraging and the rate of food intake: the preferred period of activity should be that which minimizes the predation risk per unit of food obtained. 2. However, several species of freshwater fish show flexibility in the daily pattern of feeding activity. European Minnows Phoxinus phoxinus L. prefer to feed at night at low temperatures, spending the majority of the day hiding in refuges. Since their feeding efficiency is lower at night, this behaviour is thought to minimize exposure to diurnal predators. The fish become increasingly active in the day as the temperature increases, possibly because their food requirements cannot be met by only feeding at night. 3. Here, it is tested experimentally whether nutritional state can affect the daily activity schedule, by manipulating the energy reserves of over-wintering minnows and recording their relative night- and daytime use of refuges. 4. Well-nourished fish were often observed hiding in refuges, especially during the day. As their energetic reserves decreased, they were more likely to be seen out of the refuges both by day and by night. However, the change in activity was greater by day, so that the fish became increasingly diurnal as their nutritional reserves declined. This effect was independent of temperature. 5. The results support the hypothesis that the fish attempt to minimize their exposure to diurnal predators, but must balance this against the need to increase their level of daytime foraging activity when in energy deficit. [ABSTRACT FROM AUTHOR]

Being in a refuge has benefits in terms of predator avoidance and costs in terms of lost feeding opportunities. We investigated how the relative importance of these costs and benefits changes with increasing body length in two sympatric fish species, the minnow, Phoxinus phoxinus, and the stickleback, Gasterosteus aculeatus, which differ in their morphological anti-predator adaptations. Minnows were slower to emerge after taking refuge than sticklebacks, and spent less time outside it, which is consistent with the idea that minnows, which lack the morphological defences (such as spines) of sticklebacks, are more cautious of predators than the latter. Food-deprivation experiments indicated that the costs of missed feeding opportunities in terms of relative weight loss were lower for minnows than sticklebacks. Therefore hiding in a refuge comes at a lower metabolic cost for minnows than sticklebacks. Both species reduced their hiding time when food deprived and increased it following a predation threat. Furthermore, they both showed a strong trend for longer hiding periods and shorter exploration times outside the refuge with increasing body length. Our results suggest that in sticklebacks the body length-dependence of hiding times was a result of perceived predation risks being constant with increasing body length whereas relative weight losses decreased. Thus larger fish could metabolically afford to be more cautious. In minnows, both the predation risk and metabolic expenditure decreased with increasing body length suggesting that the longer hiding times in larger fish represented a trade-off between the two factors. [ABSTRACT FROM AUTHOR]

Reduced growth occurred in yearlings and adults of the minnow Phoxinus phoxinus L. following exposure to zinc nitrate in fresh water over a 150-day period. Yearlings were more sensitive than adults and showed reduced growth at 0.13 ppm zinc (corresponding to 1/25 of the estimated 96-hr LC50). Suppressed growth was associated with reduced Tubifex consumption. [ABSTRACT FROM AUTHOR]

The behaviour of individual minnows (Phoxinus phoxinus) and goldfish (Carassius auratus) foraging on an artificial food patch was recorded for single species shoals of 2, 4, 6, 12 and 20 fish. In both species shoal size accounted for most variation in behaviour in the experiments. The behaviour of individual goldfish differed more than that of individual minnows, a result that can be explained by the weaker shoaling tendency of goldfish. 'Timid' behaviour, for example lurking in the weeds or rapid darting and turning, predominated in small shoals. It was only in large shoals that fish made frequent and lengthy visits to the patch. [ABSTRACT FROM AUTHOR]

Metacercariae of trematodes from the genus Diplostomum are major helminth pathogens of freshwater fish, infecting the eye or the brain. The taxonomy of the genus Diplostomum is complicated, and has recently been based mainly on the molecular markers. In this study, we report the results of the morphological and molecular genetic analysis of diplostomid metacercaria from the brain of the minnow Phoxinus phoxinus from three populations in Fennoscandia (Northern Europe) and one population in Mongolia (East Asia). We obtained the data on the polymorphism of the partial mitochondrial cox1 gene and ribosomal ITS1–5.8S–ITS2 region of these parasites. РСА-based morphological analysis revealed that the parasites in the Asian and the European groups of Diplostomum sp. were distinctly different. Metacercariae from the brain of Mongolian minnows were much larger than those from the brain of Fennoscandian minnows but had much fewer excretory granules. Considering that the two study regions were separated by a distance of about 4500 km, we also tested the genetic homogeneity of their host, the minnow, using the mitochondrial cytb gene. It was shown that Diplostomum -infected minnows from Mongolia and Fennoscandia represented two previously unknown separate phylogenetic lineages of the genus Phoxinus. Both molecular and morphological analysis demonstrated that the parasites from Fennoscandia belonged the species Diplostomum phoxini , while the parasites from Mongolia belonged to a separate species, Diplostomum sp. MТ. Each of the two studied Diplostomum spp. was associated with a specific, and previously unknown, genealogical lineage of its second intermediate host, P. phoxinus. • Two distinct species of ' Phoxinus phoxinus ' complex inhabit in Fennoscandia and Mongolia. • Two distinct species of ' Diplostomum phoxini ' complex parasitize brain of minnows in Fennoscandia and Mongolia. • Each of brain species is associated with specific genealogical lineages (European and Asian) of minnow as the second intermediate fish host. [ABSTRACT FROM AUTHOR]