White-spotted Charr Salvelinus Leucomaenis Research Articles

Occurrence of the white-spotted charr Salvelinus leucomaenis in Lake Biwa, central Japan

Occurrence of the white-spotted charr Salvelinus leucomaenis in Lake Biwa, central Japan

Diverse migration patterns of anadromous white-spotted charr Salvelinus leucomaenis revealed from otolith microchemistry

AbstractAnadromous migration of salmonid fish has been extensively studied, primarily focusing on the dichotomous framework of anadromy and residency. However, there remains a limited understanding of intermediate migratory behaviors within the anadromous framework. Our study aimed to classify the lifetime migration patterns of the anadromous white-spotted charr Salvelinus leucomaenis within and among populations using otolith annuli and Sr:Ca ratios. Initially, the migratory histories of anadromous charr were divided into two stages: “virgin sea-run stage” and “veteran sea-run stage”. The former was further categorized into three types: ocean entry at age ≥1+ years old, early descending, and brackish use. The latter was grouped into four types: annual migrants, frequent migrants, retired migrants, and ocean residents. We found that the proportion of migration patterns varied among rivers, with multiple patterns coexisting within the same river. Migration patterns typically involving 1–5 years spent in freshwater rivers followed by annual oceanic migrations were the most abundant, although diverse patterns were also observed. In the virgin sea-run stage, some individuals experienced the ocean at age 0+ years or brackish environments before their first sea entry. In the veteran sea-run stage, we found individuals who had resided in either the ocean or rivers for over a year. Retired migrants, characterized by stopping oceanic migration at a certain age and subsequently spending time in rivers, were exclusive to southern rivers. Conversely, ocean residents who spend one or more years in the ocean were more frequent in northern regions. Consequently, the lifetime migration patterns of anadromous white-spotted charr may exhibit stronger ocean dependency at higher latitudes. The implications of this study highlight the complexity and flexibility of migratory behaviors within and among white-spotted charr populations.

Longitudinal structuring of stream-fish assemblages: is niche partitioning observed in two-species systems applicable to three-species systems?

AbstractLongitudinal distribution and niche partitioning phenomena have been extensively reported for streams containing two salmonid species but remain poorly understood for streams containing three or more salmonid species. Herein, we examined the abiotic environmental variables and population densities of fishes, including three salmonids, in 30 reaches of the Setose River, Hokkaido, Japan, across altitudes (120–450 m) and maximum water temperature (15–26 °C) gradients to determine the distribution of major fish species in this system. The densities of white-spotted charr Salvelinus leucomaenis, southern Asian Dolly Varden Salvelinus curilus, masu salmon Oncorhynchus masou, fluvial sculpin Cottus nozawae, and stone loach Barbatula oreas varied along environmental gradients despite their wide distribution sympatrically. We further investigated the interspecific interactions between three potentially competitive salmonids, white-spotted charr, Dolly Varden, and masu salmon. We observed that in the three-species system, including upstream Dolly Varden, salmon occupied upstream areas colder than those inhabited by charr, which is contrary to the pattern reported for charr and salmon two-species systems, wherein charr are found in the colder upstream areas. In underwater observations, salmon preferred faster water velocities than charr and Dolly Varden. Dolly Varden were found exclusively on the riverbed, followed by charr, whereas salmon occurred further away from the riverbed. Analysis of the stomach contents revealed that all three salmonids depended on terrestrial insects, but only Dolly Varden consumed benthic aquatic insects. In our three-species system that included Dolly Varden (preadapted to benthos foraging), no difference was observed in the degree of terrestrial insect consumption between charr and salmon. These results are in striking contrast to the reports of charr preying on relatively more aquatic insects than those consumed by salmon in charr and salmon two-species systems. Therefore, we speculate that Dolly Varden and salmon influence interspecific interactions between charr and salmon and between charr and Dolly Varden, respectively, explaining the distinct longitudinal distribution and feeding habits observed in two- vs. three-species systems. These variant interspecific interactions among the three competing species may have driven the expansion of their sympatric zones.

DHA and EPA levels in a piscivorous fish changed by preying upon stocked salmon fry

Increases in prey population size can affect the physiology and ecology of upper-trophic level organisms. This phenomenon is known as a bottom-up effect. For example, the increased abundance of prey resources can trigger physiological (internal) changes in predators, such as improvements in nutritional status. However, these physiological aspects of bottom-up effects have not been considered. In this study, we tested the hypothesis that white-spotted charr Salvelinus leucomaenis, a salmonid fish, increases body stores of omega-3 fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), by preying upon stocked hatchery-reared masu salmon Oncorhynchus masou fry in streams. The dynamics of fatty acid contents in charr inhabiting salmon-stocked and unstocked streams clearly support this hypothesis: fatty acid contents (DHA, EPA, and total fatty acid) increased after stocking in stocked streams, but not in unstocked streams. In addition, DHA increased with increasing body size of white-spotted charr and vice versa for EPA. The impacts of human activities, such as fish stocking, on freshwater ecosystems are a matter of serious concern for conservation. Future attempts to gain a comprehensive understanding of the impacts of fish stocking should consider not only community ecology but also physiology.

Interpopulation variation of behavioural and morphological traits that affect downstream displacement of the juvenile white-spotted charr Salvelinus leucomaenis.

Downstream displacement, the passive downstream dispersal of riverine organisms, can generate evolutionary pressures that selectively remove susceptible individuals from upstream habitats. These evolutionary pressures may accumulate over time in fish populations situated upstream of a tall check dam that displaced fish are unable to swim over and can be diluted by the homing of displaced individuals in the absence of such barriers. Here, we conducted interpopulation comparisons between above-dam and unrestricted open-stream populations of the juvenile white-spotted charr Salvelinus leucomaenis to test the hypothesis that above-dam juveniles possess more advantageous traits that reduce downstream displacement than open-stream juveniles. We focused on sedentary behaviour and body depth, both of which are known to affect downstream displacement. Interpopulation comparisons revealed that juveniles from above-dam populations were consistently more sedentary than those from open-stream populations. On the other hand, there were no systematic differences in body depth between above-dam and open-stream populations. These results are consistent with the evolution of behaviours in above-dam populations that inhibit downstream displacement. However, several other factors could explain the results obtained, and further studies will be needed to confirm the presence of behavioural evolution in our study system. This article is protected by copyright. All rights reserved.

Recovery of white-spotted charr Salvelinus leucomaenis following the removal of stocked red-spotted masu salmon Oncorhynchus masou ishikawae in a small headwater tributary of Lake Biwa, central Japan

Recovery of white-spotted charr Salvelinus leucomaenis following the removal of stocked red-spotted masu salmon Oncorhynchus masou ishikawae in a small headwater tributary of Lake Biwa, central Japan

Salmincola markewitschi or S. carpionis (Copepoda: Lernaeopodidae)? A requirement for taxonomic revision due to their high morphological variations.

Salmincola markewitschi Shedko et Shedko, 2002 (Copepoda: Lernaeopodidae) is an ectoparasitic copepod mainly infecting the buccal cavities of white-spotted charr Salvelinus leucomaenis (Pallas) (Salmonidae). This species has only been recorded from Northeast Asia, where a morphologically similar congener Salmincola carpionis (Krøyer, 1837) is also distributed, using the same host species. These copepods are hard to distinguish from each other because of their similarities. We thus examined the newly collected specimens morphologically and genetically from five populations of white-spotted charr in Japan. Most of the specimens were morphologically consistent with S. markewitschi but showed great variations in the numbers of spines on the exopods of the antennae, shape of the maxilliped myxal palps, and the bulla diameter. Consequently, some specimens shared characteristics with S. carpionis. In addition to the mophological continuities, genetic analyses of 28S rDNA and COI mitochondrial DNA confirmed that all specimens belong to a single species. Further taxonomic revisions are required to draw conclusions of whether S. markewitschi is a valid species different from S. carpionis, by collecting samples from across their wide distributional ranges, such as Europe, North America, and Northeast Asia. A key to identification of species of Salmincola Wilson, 1915 occurring in Japan is also provided.

“Freshwater Components” in the Populations of Whitespotted Char Salvelinus leucomaenis (Salmonidae) in the North of the Species Range (Kamchatka)

The variety of types of life strategy and the structure of the populations of whitespotted char Salvelinus leucomaenis (Pallas, 1814) are considered at Kamchatka. At the north of the species range, the populations of whitespotted char are heterogeneous. The main role in reproduction belongs to anadromous whitespotted char, but there are also the groups in the populations that realize their life cycle exclusively in fresh waters. Dwarf males are common in the rivers of different types. In the geomorphologically complex river (Kol), there is also the river populations of rheodromous whitespotted char, represented by males and females. Favorite biotopes (blockages and creases of woody material on deep reaches, found only in foothill rivers) are key parameters predetermining the presence of a river population of rheodromous whitespotted char. At the north of the species range, the variety of individuals with different types of life strategy in whitespotted char is comparable to that observed in the southern parts, in particular, in the basin of the Sea of Japan, which is considered the zone of the ecological optimum of the species.

Evidence for Introgressive Hybridization between Native Dolly Varden (Salvelinus curilus (syn. Salvelinus malma)) and Introduced Brook Trout (Salvelinus fontinalis) in the Nishibetsu River of Hokkaido, Japan.

Hybridization is one of the negative outcomes for the introduction of non-native species, which can lead to rapid displacement and genetic extinction of native species. Salmonid fishes have been widely introduced outside of their native ranges for food supply and recreational fishing. Here, we investigate the occurrence of introgressive hybridization among native Dolly Varden (Salvelinus curilus (syn. Salvelinus malma)), white-spotted charr (Salvelinus leucomaenis), and introduced brook trout (Salvelinus fontinalis), in streams of the Nishibetsu River, Hokkaido, Japan. Microsatellite DNA analysis detected five hybrids between native Dolly Varden and introduced brook trout. This is the first evidence for hybridization between native Dolly Varden and introduced brook trout, while the latter has been known to hybridize with many other salmonids. Furthermore, incongruence between mitochondrial DNA and microsatellite DNA analyses suggested introgression among the three Salvelinus species. Further studies to estimate the hybrid fitness are necessary to understand how hybridization among the three species affects the native species.

Artificially increased habitat complexity reduces predation-induced mortality for juvenile salmon in simplified environments

Many river systems have been artificially modified for various reasons worldwide. Although simplified riverbeds due to artificial modifications often alter the species compositions and interactions, methods for mitigating habitat degradation in such rivers are underdeveloped. In this study, we evaluated the effects of tree branches on the survival of juvenile masu salmon Oncorhynchus masou under predation risk by piscivorous fish (White-spotted charr Salvelinus leucomaenis) in artificially simplified environments. We found that 0.4 m2 or more of tree branches per 1.0 m2 of artificial concrete pond doubled the survival of juvenile salmon for 20 days. In addition, body sizes of predator and prey did not have a significant effect on salmon survival, whereas the number of branches did in this experiment. These results indicate that adding structural complexity can mitigate predation pressure by piscivorous fish in artificially simplified environments. This study provides important guidelines for the management and restoration of suitable habitats for stream salmonids in artificially simplified environments where the main predators are piscivorous fish.

Interspecific social dominance networks reveal mechanisms promoting coexistence in sympatric charr in Hokkaido, Japan.

Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n=761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.

NEMATODES OF GENUS PHILONEMA (PHILONEMIDAE) FROM SOCKEYE SALMON AND WHITESPOTTED CHAR FROM LAKE KISI (OLA RIVER BASIN, OKHOTSK SEA)

Morphology of phylonems infesting whitespotted char Salvelinus leucomaenis and sockeye salmon Oncorhynchus nerka in Lake Kisi at the northern coast of the Okhotsk Sea is described for the first time. Sockeye was infected with adults of Philonema oncorhynchi Kuitunen-Ekbaum, 1933 and larvae of other nematode species (Philonema sp. II), and char — with adult dracunculoid nematode designated as Philonema sp. I. This Philonema sp. I differs considerably from Ph. oncorhynchi by number of reproductive papillae, their distribution, and structure of cuticular appendices on the caudal end of males. Larvae of Philonema sp. I (1st stage) and Philonema sp. II (3rd stage) are described, as well. These new data allow to reconsider the species belonging of nematodes infesting chars (Salvelinus) in North-East of Russia, which are identified now mostly as Ph. oncorhynchi.

Effectiveness of fry stocking to enhance the white-spotted charr Salvelinus leucomaenis population in the Nakatagiri River, central Japan

Effectiveness of fry stocking to enhance the white-spotted charr Salvelinus leucomaenis population in the Nakatagiri River, central Japan

Displacement of native white-spotted charr Salvelinus leucomaenis by non-native brown trout Salmo trutta after resolution of habitat fragmentation by a migration barrier.

After resolution of habitat fragmentation by an erosion-control dam, non-native brown trout Salmo trutta invaded the upstream side of the dam and displaced native white-spotted charr Salvelinus leucomaenis in Monbetsu stream, Hokkaido, northern Japan.

Differentiated predation risk on hatchery-reared juvenile masu salmon by white-spotted charr with different body sizes

Predation after release is one of the major concerns of hatchery fish propagation. However, size-specific interaction between predator and prey on the survival of hatchery-released salmonid fish is largely unknown. To understand the size-selective predation risk, 24-h predation experiments were conducted on masu salmon Oncorhynchus masou in tanks. Four ranges of fork length (FL) were examined for masu salmon as a prey, in combination with three ranges of FL for white-spotted charr Salvelinus leucomaenis as a predator. The results show that not only predator and prey sizes, but also interaction between prey size and predator size, strongly affected the survival rate of masu salmon. Predation on masu salmon with the FL exceeding 40% of the FL of white-spotted charr was rare in the experiment. A logistic regression suggests that 37% relative FL of masu salmon to white-spotted charr results in the 50% survival of masu salmon. Our results suggest that adjusting relative size of hatchery fish to the size of local fish predators at the time of hatchery release will have a significant impact on the survival of hatchery fish in the wild. From this perspective, site-specific, adaptive management might be important to improve the effectiveness of hatchery fish propagation.

Isolation and characterization of tri- and tetra-repeat microsatellite loci in the white-spotted charr Salvelinus leucomaenis (Salmonidae).

Tri- and tetra-motif repeat microsatellite marker loci were developed for the white-spotted charr Salvelinus leucomaenis. The 454 pyrosequencing was used to discover repeat arrays, and eight microsatellite-primer sets, available for the estimation of polymorphisms, were identified. The number of alleles in a wild population ranged from two to four and the observed and expected heterozygosities were 0·180-0·600 and 0·188-0·599, respectively.

Fish assemblages in headwater tributaries of the Agano River System, Japan

The present study examined fish assemblages in ten tributaries with different environmental characteristics in the upper drainages of the Agano River system, northern Honshu, Japan. Seven fish species (five families) were found in the 10 tributaries examined. White-spotted charr Salvelinus leucomaenis and sculpin Cottus pollux were common in almost all tributaries. Masu salmon Onchorhynchus masou masou inhabited the tributaries at relatively low densities despite intensive stocking in the study region. No statistically significant relationships between local environmental factors and the number of species captured were found. However, all seven species, including age-0 fish of each species, were recorded in the tributary with the lowest gradient and second-narrowest stream width, suggesting that small tributaries potentially provide an important habitat for a diverse range of species. The relative density of white-spotted charr in tributaries subject to fishing prohibition was higher on average than that in tributaries not subjected to fishing prohibition, suggesting that fishing depresses the abundance of white-spotted charr.

Do stocked hatchery‐reared juveniles ecologically suppress wild juveniles in Salvelinus leucomaenis?

The dominancy of semi-wild and hatchery-reared white-spotted charr Salvelinus leucomaenis juveniles was evaluated using pair-wise enclosure tests and field stocking tests. The semi-wild S. leucomaenis originated in a hatchery, being stocked into the test stream as eyed-eggs. In the pair-wise enclosure test, the semi-wild S. leucomaenis dominated the hatchery S. leucomaenis that were of a similar standard length (L(S) ). The semi-wild S. leucomaenis were subordinate to hatchery S. leucomaenis that were > 11% larger in LS . In the field stocking test, the abundance and growth of semi-wild S. leucomaenis was decreased in the presence of larger hatchery S. leucomaenis (14% larger LS ). Taken together, these results suggest that larger hatchery S. leucomaenis ecologically suppress the smaller semi-wild S. leucomaenis. Salvelinus leucomaenis juveniles that are stocked with the intention of supplementing natural populations should be < 10% larger than their wild counterparts at the time of stocking to minimize their competitive advantage. The semi-wild and hatchery S. leucomaenis used in both tests were genetically similar individuals, suggesting that the differences are due to the early rearing environment of either a natural stream or hatchery. The hatchery S. leucomaenis have lower levels of aggression as a result of selection in the hatchery rearing environment. Rearing in a natural stream from the eyed-egg stage is likely to increase their lowered aggression.

Two complete mitochondrial genome sequences of white-spotted char Salvelinus leucomaenis (Salmoniformes: Salmonidae)

We sequenced two complete mitochondrial genomes of the white-spotted char Salvelinus leucomaenis from two wild populations. The complete genome is 16,655 bp in size and its gene content, arrangement, codon usage and base composition are identical with those observed in salmonids. The detailed comparison with other complete mitochondrial genomes of Salvelinus revealed signs of recombination in one of them.

Population genetic differentiation of white-spotted char Salvelinus leucomaenis (Pallas) in Russian Far East

The genetic structure of the populations in white-spotted char Salvelinus leucomaenis (family Salmonidae) was determined based on variations in ten microsatellite DNA loci in samples from different parts of the species range in the Russian Far East. In a number of samples, variations in 21 allozyme loci were examined, of which five loci were found to be polymorphic. The overall diversity level in the examined markers was comparable to that observed in a closely related char species, Dolly Varden. The estimates of interpopulation genetic differentiation were highly statistically significant in most of the pairwise comparisons amongthe samples. The overall evaluation of the spatial genetic differentiation in white-spotted char constituted F(ST) = 0.203 and R(ST) = 0.202. Cluster analysis and multidimensional scaling based on microsatellite allele frequencies indicated the possible subdivision of the examined samples into two main groups, i.e., northern (represented by the regions of the north of Khabarovsk krai, Kamchatka, Yama Bay) and southern (with regions including Sakhalin, Primorye, and the Kuril Islands). The allozome data demonstrated a similar pattern of differentiation. The level of intra- and interpopulation genetic diversity in the southern group was higher than in the northern group. The isolation-by-distance test did not identify a significant correlation between genetic and geographic distances among the samples. The data obtained enabled the suggestion that the genetic structure of the population of white-spotted char was shaped by the influence of historical geological climatic rearrangements of its range and the genetic drift, because of determined by relatively low population number and limited in the extent of the migration activity of its anadromous form.