Marble Trout Salmo Marmoratus Research Articles

Size-age population structure of an endangered and anthropogenically introgressed northern Adriatic population of marble trout (Salmo marmoratus Cuv.): insights for its conservation and sustainable exploitation.

Salmonid species are main actors in the Italian socio-ecological landscape of inland fisheries. We present novel data on the size-age structure of one of the remnant Italian populations of the critically endangered marble trout Salmo marmoratus, which co-occurs with other stocked non-native salmonids in a large glacial river of the Lake Maggiore basin (Northern Italy-Southern Switzerland). Like other Italian native trout populations, the Toce River marble trout population is affected by anthropogenic introgression with the non-native brown trout S. trutta. Our sample includes 579 individuals, mainly collected in the Toce River main channel. We estimated the length-weight relationship, described the population size-age structure, estimated the age-specific growth trajectories, and fit an exponential mortality model. A subset of the sample was also used to measure numerical and biomass density. The estimated asymptotic maximum length is ~105 cm total length (TL). Mean length at first maturity is ~55 cm TL, and mean length at maximum yield per recruit is ~68 cm TL. Approximately 45-70% of the population are estimated to die annually, along with a fishing annual mortality of ~37%, with an exploitation ratio of ~0.5. The frequency distribution of length classes in a sample collected by angling shows that ~80% of the individuals that could be retained according to the current recreational fishing regulations likely never reproduced, and large fish disproportionally contributing to recruitment are fished and retained. We identify possible overfishing risks posed by present regulations, and propose updated harvest-slot length limits to mitigate such risks. More detailed and long-term datasets on this system are needed to more specifically inform the fishery management and monitor the effects of any change in the management strategy on the size-age structure of the marble trout population of the Toce River.

Within-individual trophic variability drives short-term intraspecific trait variation in natural populations.

Intraspecific trait variability (ITV) maintains functional diversity in populations and communities, and plays a crucial role in ecological and evolutionary processes such as trophic cascades or speciation. Furthermore, functional variation within a species and its populations can help buffer against harmful environmental changes. Trait variability within species can be observed from differences among populations, and between- and within individuals. In animals, ITV can be driven by ontogeny, the environment in which populations live and by within-individual specialization or variation unrelated to growth. However, we still know little about the relative strength of these drivers in determining ITV variation in natural populations. Here, we aimed to (a) measure the relative strength of between- and within-individual effects of body size on ITV over time, and (b) disentangle the trophic changes due to ontogeny from other sources of variability, such as the environment experienced by populations and individual preferences at varying temporal and spatial scales. We used as a model system the endangered marble trout Salmo marmoratus, a freshwater fish living in a restricted geographical area (<900km2 ) that shows marked changes in diet through ontogeny. We investigated two trophic traits, trophic position and resource use, with stable isotopes (δ15 N and δ13 C), and followed over time 238 individually tagged marble trout from six populations to estimate the trophic changes between and within individuals through ontogeny at three different time-scales (short term: 3months, medium term: 1year and long term: 2years). We found that the relative strength of between- and within-individual effects of body size on trophic position and resource use change strongly over time. Both effects played a similar role in ITV over medium- and long-term time-scales, but within-individual effects were significantly driving trophic variability over short-term scales. Apart from ontogenetic shifts, individuals showed variability in trophic traits as big as the variability estimated between populations. Overall, our results show how the relative strengths of ITV drivers change over time. This study evidences the crucial importance of considering effects of time-scales on functional variability at individual, population and species levels.

Analysis of the reproductive cycle of female wild marble trout Salmo marmoratus in a prealpine brook of the Soča River basin (Northeast Italy)

The reproductive cycle of female wild marble trout Salmo marmoratus was studied in a prealpine watercourse (Northeast Italy). Gonadosomatic index, oocyte growth and plasma levels of 17β-oestradiol and testosterone were bimonthly measured during one year to obtain a detailed dataset and to gain useful tools for the identification of the reproductive stage without impact for the species. Monitored features showed significant variations during the study period: gonadosomatic index and oocyte size increased slightly but significantly during the first part of the cycle (from February to June), while steroid levels remained quite constant; for all parameters, major increases were highlighted between August and the spawning season (which occurred from the middle of November to the middle of December). Ranges and trends observed for gonadosomatic index (from 0.87 ± 0.41% to 10.91 ± 3.37%) and oocyte diameter (from 0.692 ± 0.031 mm to 4.624 ± 0.208 mm) were generally in agreement with literature regarding salmonids, while plasma levels of 17β-oestradiol (from 0.214 ± 0.015 ng ml−1 to 78.090 ± 23.882 ng ml−1) and testosterone (from 0.327 ± 0.086 ng ml−1 to 71.800 ± 29.406 ng ml−1) showed wider ranges. A strong non-linear relationship was found between oocyte size and 17β-oestradiol plasma concentration (r2 = 0.890) and especially between oocyte size and testosterone plasma concentration (r2 = 0.947). This last relationship could likely be used to obtain information relative to the gonadal development, especially in the case of an endangered species like Salmo marmoratus, which needs non-invasive tools for management.

Within- and among-population variation in vital rates and population dynamics in a variable environment.

Understanding the causes of within- and among-population differences in vital rates, life histories, and population dynamics is a central topic in ecology. To understand how within- and among-population variation emerges, we need long-term studies that include episodic events and contrasting environmental conditions, data to characterize individual and shared variation, and statistical models that can tease apart shared and individual contribution to the observed variation. We used long-term tag-recapture data to investigate and estimate within- and among-population differences in vital rates, life histories, and population dynamics of marble trout Salmo marmoratus, an endemic freshwater salmonid with a narrow range. Only ten populations of pure marble trout persist in headwaters of Alpine rivers in western Slovenia. Marble trout populations are also threatened by floods and landslides, which have already caused the extinction of two populations in recent years. We estimated and determined causes of variation in growth, survival, and recruitment both within and among populations, and evaluated trade-offs between them. Specifically, we estimated the responses of these traits to variation in water temperature, density, sex, early life conditions, and extreme events. We found that the effects of population density on traits were mostly limited to the early stages of life and that growth trajectories were established early in life. We found no clear effects of water temperature on vital rates. Population density varied over time, with flash floods and debris flows causing massive mortalities (>55% decrease in survival with respect to years with no floods) and threatening population persistence. Apart from flood events, variation in population density within streams was largely determined by variation in recruitment, with survival of older fish being relatively constant over time within populations, but substantially different among populations. Marble trout show a fast to slow continuum of life histories, with slow growth associated with higher survival at the population level, possibly determined by food conditions and age at maturity. Our work provides unprecedented insight into the causes of variation in vital rates, life histories, and population dynamics in an endemic species that is teetering on the edge of extinction.

Temporal changes in allele frequencies in a small marble trout Salmo marmoratus population threatened by extreme flood events.

The effect of extreme floods on the genetic composition of marble trout Salmo marmoratus living in Lipovscek, a tributary of the Soca River in Slovenia, which has been affected by multiple destructive flood events for centuries was investigated. By monitoring genetic variability during the period 2004-2011, apparent signatures of genetic erosion including a decline in observed and expected heterozygosities and allelic richness were observed. Contemporary effective population size was estimated between 11 and 55 individuals, which is congruent with census data. The data suggest asymmetric gene flow between the two sections of the river. The existence of substantial downstream migration (15-19%) was confirmed by paternity analysis. A small (1-3%) upstream migration was also suggested, which was confirmed by tagging data. Overall, low genetic diversity has not prevented the survival of the Lipovscek population, which might be a common feature of salmonid freshwater populations.

Metabolic characteristics of early life history stages of native marble trout (Salmo marmoratus) and introduced brown trout (Salmo trutta) and their hybrids in the Soča River

AbstractMetabolic potential and respiration rate have been measured in the early life stages of native marble trout Salmo marmoratus (MT), introduced brown trout Salmo trutta (BT) and their hybrids (MH = female of MT × male of BT and BH = female of BT × male of MT) to examine the differences in their metabolic characteristics. Metabolic potential and respiration rate were lowest in each developmental stage in MT, followed by MH, BT and BH. The ratio between metabolic potential and respiration rate (ETS/R) in larvae was also lowest for MT (1.0) and MH (1.1), followed by BT (1.4) and BH (1.6), indicating more intensive exploitation of metabolic potential for actual respiration in MT (100%) and MH (~90%) than in BT (~70%) and BH (~60%). Lower ETS/R means a disadvantage in the case of enhanced metabolic activity due to insufficient enzyme machinery needed for energy production. Thus, potential and actual metabolic activity and ETS/R ratio could account for the different competitive abilities among pure trout species and their hybrids in a particular environment. This is the first report on biochemical and physiological differences between pure MT and their hybrids. The combination of metabolic and respiration rate measurements appears to be a useful tool for estimating the metabolic properties in the early developmental stages of fish.

Susceptibility of genotyped marble trout Salmo marmoratus (Cuvier, 1829) strains to experimental challenge with European viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV)

Abstract The marble trout Salmo marmoratus (Cuvier, 1829) is an endemic species of great conservation concern, given its geographical restricted distribution and the high risk of hybridization with brown trout Salmo trutta L. Viral hemorrhagic septicemia (VHS) and infectious hematopoietic necrosis (IHN) are predominantly diseases of freshwater salmonids, which may trigger off severe disease outbreaks causing high mortality. Marble trout has not been inserted in the vector species list for those pathogens, but at present, little information on its susceptibility and on the possible carrier status is available. The aim of the present study was to assess the ability of European strains of VHSV and IHNV to cause disease and associated mortality in experimentally infected marble trout, and to determine whether a carrier status can result after experimental infection. Three genetically different strains of marble trout were challenged with VHSV and IHNV by immersion. Rainbow trouts were used as positive controls. Fish were checked twice a day, and dead fish were removed and sampled for subsequent virological analyses. With respect to rainbow trout, results demonstrated a very low susceptibility of marble trout to both VHSV and IHNV under simulated natural conditions. The presence of a certain number of chronically infected marble trout confirms that some individuals can survive the infection and eventually act as carrier of the disease, suggesting that marble trout should be definitely added to the list of susceptible species according to the European legislation.

Determining individual variation in growth and its implication for life-history and population processes using the empirical Bayes method.

The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups) determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function's parameters k (rate of growth) and (asymptotic size). Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC), the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish.

Eco-evolutionary dynamics induced by massive mortality events.

An eco-genetic model tuned on a population of marble trout Salmo marmoratus subject to periodic flood events was used to explore how the evolution of growth rates interacting with density-dependent processes can modify size at age and population structure and in turn influence the resilience of populations. Fish with greater growth potential were assumed to have higher mortality rates. The results of simulations were compared between two scenarios, one in which populations may evolve growth rates and the other one in which the distribution of growth rates within a population is kept fixed. Evolving populations had a greater proportion of age 1 year individuals in the population, greater median length at age 3 years (the typical age at sexual maturity for S. marmoratus) and lower population sizes. The slightly smaller population sizes did not affect realized extinction risk. Resilience, defined as the number of years necessary to rebound from flood-induced population collapse, was on average from 2 to 3 years in both scenarios, with no significant difference between them. Moderate heritability of growth, relaxation of density-dependent processes at low densities and rapid recovery to a safe population size combine to limit the capacity to evolve faster recovery after flood-induced population collapses via changing growth rates.

First marine record of marble trout Salmo marmoratus

A specimen of marble trout Salmo marmoratus, of 955 mm total length (L(T) ) and weighing 10 220 g, was caught on 26 December 2008 by a commercial fisherman near the coast of Igrane (eastern Adriatic Sea). This represents the first marine record of this species.

Empirical standard mass equation forSalmo marmoratus

Total length (L(T)) (range 24-1000 mm; mean ±S.E. = 170.21 ± 0.36 mm) and mass (W) (range 0.10-9590 g; mean ±S.E. = 76.03 ± 0.87 g) of 36,460 specimens of marble trout Salmo marmoratus were used to compute a standard mass (W(s)) equation for this species by means of the empirical percentile (EmP) method. The EmP W(s) equation calculated was: log(10) W(s) = -5.208 + 3.202 log(10) L(T) - 0.046 (log(10) L(T))(2) (L(T) range 90-570 mm) and it is valid throughout the species' area of distribution across Europe.

Morphological differences in the skin of marble trout &lt;i&gt;Salmo marmoratus&lt;/i&gt; and of brown trout &lt;i&gt;Salmo trutta&lt;/i&gt;

Despite being genetically very closely related, the marble trout Salmo marmoratus and the brown trout Salmo trutta exhibit marked phenotypic differences, particularly with regard to skin pigmentation. Histological analysis of skin from the head and gill cover of differently aged individuals of the two species was carried out in order to characterize differences in skin structure. The basic structure of skin of the individuals studied corresponded with that described for other salmonids, though the head epidermis was somewhat thicker in S. marmoratus than in S. trutta, thickening with age in both species. Numerous secretory goblet cells and sporadic secretory sacciform cells were observed in the upper and middle part of the epidermis in both species. Melanophores were present in both species only in the dermis, and were bigger in S. marmoratus and present at lower average density than in S. trutta, and more or less constant across all age classes. In adult S. marmoratus with fully established marble pigmentation, light areas at low density with small (i.e. aggregated) melanophores were present, while in S. trutta melanophores were more uniformly distributed.

Translocation of stream-dwelling salmonids in headwaters: insights from a 15-year reintroduction experience

Translocation programs are a common strategy to increase the number of viable populations of threatened freshwater fishes. Yet, only in a minority of cases the success or failure of translocations has been assessed through a quantitative analysis of demographic traits, compensatory responses, life-histories and population dynamics of the threatened species. A paradigmatic case a translocation program combining both management- and research-oriented activities is represented by the Marble Trout Conservation Program, which started in 1993 in the upper reaches of the Soca, Idirjca and Baca river basins (Slovenia) for the conservation of stream-dwelling marble trout Salmo marmoratus. In order to enhance the viability of the species, two new populations were created in 1996 by stocking 500 marble trout aged 1+ in previously fishless streams (Gorska and Zakojska) within the core habitat of the species. The new populations have been systematically monitored for 15 years by individually tagging and sampling marble trout. Our analyses show that deterministic extinction of marble trout populations are unlikely and that high-magnitude environmental stochasticity (i.e., severe floods) is the only main cause of local population extinction, despite the high resilience to flood-induced massive mortalities exhibited by marble trout through compensatory mechanisms (e.g., relaxation of density-dependent body growth and survival at low densities). Fishless headwaters, probably characterized by a history of recurrent severe floods, should not be considered as candidate sites for the creation of new populations. Fewer individuals than originally reintroduced (i.e., 500 fish aged 1+ in each stream) might be sufficient to establish viable populations, since compensatory mechanisms are likely to regulate population size around stream carrying capacity in a few years. Besides enhancing the species viability, translocation programs can provide an excellent framework for the estimation of ecological traits (e.g., life-histories, demography, population dynamics etc.), identify potential vulnerabilities and thus guide well-formed management actions for the threatened species.

Innocent until proven guilty? Stable coexistence of alien rainbow trout and native marble trout in a Slovenian stream

To understand the consequences of the invasion of the nonnative rainbow trout Oncorhynchus mykiss on the native marble trout Salmo marmoratus, we compared two distinct headwater sectors where marble trout occur in allopatry (MTa) or sympatry (MTs) with rainbow trout (RTs) in the Idrijca River (Slovenia). Using data from field surveys from 2002 to 2009, with biannual (June and September) sampling and tagging from June 2004 onwards, we analyzed body growth and survival probabilities of marble trout in each stream sector. Density of age-0 in September over the study period was greater for MTs than MTa and very similar between MTs and RTs, while density of trout ≥age-1 was similar for MTa and MTs and greater than density of RTs. Monthly apparent survival probabilities were slightly higher in MTa than in MTs, while RTs showed a lower survival than MTs. Mean weight of marble and rainbow trout aged 0+ in September was negatively related to cohort density for both marble and rainbow trout, but the relationship was not significantly different between MTs and MTa. No clear depression of body growth of sympatric marble trout between sampling intervals was observed. Despite a later emergence, mean weight of RTs cohorts at age 0+ in September was significantly higher than weight of both MTs and MTa. The establishment of a self-sustaining population of rainbow trout does not have a significant impact on body growth and survival probabilities of sympatric marble trout. The numerical dominance of rainbow trout in streams at lower altitudes seem to suggest that while the low summer flow pattern of Slovenian streams is favorable for rainbow trout invasion, the adaptation of marble trout to headwater environments may limit the invasion success of rainbow trout in headwaters.

Individual growth and its implications for the recruitment dynamics of stream‐dwelling marble trout (Salmo marmoratus)

Vincenzi S, Crivelli AJ, Jesensek D, De Leo GA. Individual growth and its implications for the recruitment dynamics of stream‐dwelling marble trout (Salmo marmoratus). Ecology of Freshwater Fish 2010: 19: 477–486. © 2010 John Wiley &amp; Sons A/SAbstract – The role of density‐dependent individual growth in the recruitment dynamics of fish populations has rarely been analysed in a quantitative framework. Variations of mean size of juveniles in response to changes in population densities have frequently been observed in salmonids and it has been shown that body‐size differences at the juvenile stage can persist through the sub‐adult and adult stage. As fecundity and sexual maturation are often a function of body size, inter‐cohort variations in individual growth may ultimately affect the reproductive output and, consequently, the amount of yearly recruitment. Here, we present a simulation analysis investigating the effects of density‐dependent growth on the reproductive output and, ultimately, on the population dynamics of stream‐dwelling salmonids. The demographic model used for the numerical analysis was parameterised using marble trout Salmo marmoratus as a reference species and explicitly accounted for the occurrence of major floods events causing the population to collapse to very low densities. Our simulations showed that density‐dependent individual growth is a powerful mechanism to foster population resilience through compensatory recruitment. In addition, we argue that density‐dependent growth also helps regulate recruitment at high population densities. We show that even slight variations in the growth trajectories of fish substantially affect the size and the dynamics of the population.

The management of small, isolated salmonid populations: do we have to fix it if it ain't broken?

In their recent paper, Sato H Gharrett et al., 1999; McGinnity et al., 2003; Tallmon et al., 2004), but claimed the close geographical proximity, similar habitat and small genetic differences among remnant populations might considerably reduce this risk. In a recent review, Edmands (2007) stated that concerns over outbreeding should be taken seriously, as the effects of outbreeding can be, in some cases, as damaging as severe inbreeding. Here, we raise concerns about mixing of populations as a strategy to increase genetic variation, and we bring evidence of likely outbreeding depression observed in the rehabilitation project of the endangered freshwater salmonid marble trout Salmo marmoratus, started in Slovenia in 1993 (Crivelli et al., 2000). Since the beginning of the rehabilitation project, four marble trout populations went extinct due to landlsides (Predelica) and severe flood events (Gorska, Sventarska and Zakojska). The seven remnant populations of marble trout living in Slovenian streams are genetically distant (FST=0.66, Fumagalli et al., 2002), present a very low effective population size (for the Huda Grapa population a total population size ranging from 29 to 60 individuals was estimated between 2000 and 2007) and very low genetic variability estimated at 14 microsatellite loci (for Huda Grapa Ho=0.046, Fumagalli et al., 2002). In order to expand the genetic variability of marble trout living in the watershed, a new population (Gatsnik) was created in 1998 in a previously fishless stream by mixing the progeny of marble trout from two remnant populations from isolated streams with similar habitat (Trebuscica and Lipovesck). After two generations, the population of Gatsnik presented the typical features associated with maladaptation and outbreeding depression, that is lower annual survival rate (0.39 0.02 for trout born in the stream, higher than 0.55 for other marble trout populations living in the study area, Vincenzi et al., 2008), reproductive underperformance at the F2 generation and unusual morphological abnormalities (Fig. 1). Moreover, preliminary results from a egg-to-fry experiment performed in the fish farm for the F1 generation of Gatsnik showed 80.4% of mortality from fertilization to hatching (35.6 29.2% for the remnant populations) (D. Jesensek, pers. comm.). The translocation experiment in Gatsnik is still ongoing and may provide unequivocal evidence of outbreeding effects in 3–4 years. Nevertheless, despite the striking contrast of salmonid species in lifehistory traits may hinder generalizations, what we observed in the marble trout population of Gatsnik urges now further considerations on the opportunity of mixing populations of salmonids to increase their genetic variability. As recently reviewed by Willi et al. (2006), small populations are predicted to have low potential to adapt to environmental changes, as genetic variation and potential response to selection should be positively related to population size. Moreover, individuals in small populations may have lower fitness and be inbred, which may decrease an adaptive response to unpredictable environmental changes. Apart from the obvious cases of overexploitation, pollution and human-induced fragmentation, the small population size and low heterozygosity frequently observed in endemic

Potential factors controlling the population viability of newly introduced endangered marble trout populations

While several population viability analyses (PVAs) have been performed on anadromous salmonids, less attention has been given to stream-living salmonids. In this work, we explore the role of PVA as a tool in the recovery of threatened stream-living salmonid species. The analysis has been performed with reference to marble trout Salmo marmoratus, a salmonid with a limited geographic distribution and at risk of extinction due to hybridization with the non-native introduced brown trout. Demographic parameters, such as survival, fecundity and density-dependent patterns were estimated from an eight year on-going monitoring program of two translocated marble trout populations in pristine, previously fishless streams (Zakojska and Gorska) in the Soca and Idrijca river basins (Slovenia). To explore the importance of disturbance events such as floods on marble trout population dynamics, we performed a PVA under three scenarios: (1) occurrence of both severe and moderate floods; (2) occurrence of only moderate floods; (3) no flood events. Our analysis shows that population viability is threatened only by severe flood events, otherwise the two populations prove to be fairly stable with population abundance fluctuating around stream carrying capacity. A sensitivity analysis performed on model parameters highlighted that density-dependence in first-year survival and the magnitude of reduction in population size after a severe flood are the two most crucial parameters affecting population abundance and quasi-extinction probability, respectively. While only extreme floods can drive the population to extinction, the increase in juvenile survival when population abundance collapses after a major flood may allow the populations to quickly recover from few reproductive individuals back to stream carrying capacity.

Early survival of marble trout Salmo marmoratus: evidence for density dependence?

Abstract – The role of endogenous and exogenous factors in regulating population dynamics of freshwater salmonids is still a matter of debate. The aim of the present work was to assess the relative importance of density-dependent and -independent factors in determining the survival of marble trout (Salmo marmoratus) yearlings in two populations living in Slovenian streams (Zakojska and Gorska). The investigation was performed by combining a classical life table analysis with Monte Carlo simulation. Size-dependent fecundity was estimated by stripping wild adults in the fish farm. A significant positive relationship was found between length of marble trout females and the number of eggs produced. Egg density was the major determinant of survival from eggs to age 1+ (σ0) in both streams. Residuals of the relationship between σ0 and egg density were positively correlated with rainfall only in Zakojska, probably because, within a certain range, more intense rainfalls increases stream flow and, consequently, suitable habitat for trout. Our study shows how density-dependent and environmental factors can interact to determine the survival of marble trout during the first year of life.

Trout Salmo spp. complex in Serbia and adjacent regions of the western Balkans: reconstruction of evolutionary history from external morphology

The multivariate phenetic approach to the classification of Salmo spp. samples from Serbia and adjacent regions of western Balkans for 22 continuous external morphological characters suggests the occurrence of the following distinct stocks: West Danubian (Crno Osoje Stream and upper Zeta River) Salmo taleri, marble trout Salmo marmoratus (Trebuščica River), hatchery‐reared Atlantic Salmo trutta, Mlava River drainage (Mlava and Krupaja rivers and Buk Stream) trout Salmo cf. trutta, Velika Morava River system (Godljevača, Bela and Resava rivers) trout S. cf. trutta, Ohrid Lake belvica Salmo ohridana and Aegean coastal drainage Salmo macedonicus (Božica River). In contrast to the phenetic similarity, the phylogenetic reconstruction places the Lake Ohrid belvica as part of an unresolved polytomy with other trout groups. Salmo cf. trutta in the Mlava River appears to form the basal group for the trout species in the region. The position of marble trout implies its independent and more recent origin from the West Danubian trout stock.