Japanese Mountain Stream Research Articles

Species‐specific foraging behavior and diets of stream salmonids: An implication for negative impacts on native charr by nonnative trout in Japanese mountain streams

AbstractSalmonids have been introduced globally as a food source and recreational fishing target. In Japan, brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis) were introduced in the 19th century and have since spread. In many headwater streams, native white‐spotted charr (Salvelinus leucomaenis) are thought to be experiencing negative impacts from these species. The current study examined foraging behavior, microhabitat use, and diet overlap of these three species in Kamikochi, Nagano Prefecture: one of Japan's premier mountain areas. In Kamikochi, many spring‐fed headwater streams are currently dominated by these invasive salmonids and white‐spotted charr have declined drastically over the last half century. Underwater video analysis revealed that while total foraging rates and foraging modes were similar between the three species, brook trout and white‐spotted charr foraged benthically more frequently than brown trout. Microhabitat water depth and flow velocity were similar between species, and fish size had a positive effect on water depth and flow velocity in all three species. Diet analysis indicated that brook trout and white‐spotted charr diets were nearly identical, comprised primary of aquatic invertebrates, while brown trout preyed on a mix of terrestrial and aquatic invertebrates, as well as amphibians and fish. These results indicate that in Kamikochi, the decline of white‐spotted charr is likely most influenced by direct competition with brook trout for prey resources. However, brown trout likely also predate on juvenile white‐spotted charr, while also possibly causing a foraging niche shift of white‐spotted charr, and have ecosystem‐level impacts due to predation on terrestrial prey.

Life cycles and larval and pupal habitats of eleven Japanese Rhyacophila (Trichoptera) species at the mountain streams in central Honshu

The life cycles and microhabitats involved in aquatic stages of eleven Rhyacophila Stephens, 1836 species living in two neighboring Japanese mountain streams in Nara Prefecture, central Honshu, were investigated. Eight species had univoltine life cycles; seven species had spring to early summer emergence seasons. One species had an autumnal emergence. Four univoltine species had periods where no larvae or pupae were collected in aquatic stages, possibly a period of egg diapause. Three species had bivoltine life cycles, with early summer and autumn emergence seasons. Rhyacophila nipponica Iwata, 1927, R. manuleata AV Martynov, 1934, and R. shikotsuensis Iwata, 1927, in the nigrocephala species group Ross, 1956, have larvae which spend most of their larval stage in the hyporheos. The larvae of R. transquilla Tsuda, 1940, also inhabit the hyporheic zone, although the vertical microhabitat used by this species differed from the former three species. All four of these species have hyporheic larval stages, but in these species the first and final instar larvae reside on the surfaces of cobbles. The first instar larvae seem to live on stone surfaces immediately after hatching, and subsequently move to the interstices of sand. Final instar larvae live in the interstices of sandy bottom, and move to stone surfaces for pupation. Eleven species of the genus Rhyacophila had diverse life histories, microhabitat preferences, and experienced differing water temperature regimes during larval stages at the sites. Life history and habitat preference variation enhances the species richness of the genus and coexistence of species in upper stream of the Kinokawa River.

Geology‐Climate Interactions are Key Determinants of Climate‐Change Refugia in Japanese Mountain Streams

Photo 1. Example of the confluence of a volcanic and nonvolcanic stream (left panel). The right panel is a thermal photograph of the confluence taken using a TVS-500 camera (Nippon Avionics Co., Ltd.) on September 17, 2019, where blue colors correspond to the cold water from the volcanic stream mixing with the warmer (orange) water from the nonvolcanic stream. Photo credit: Kenta Iwasaki. Photo 2. View of a volcanic stream, Ponnunobe stream, the Sorachi river, Hokkaido, Japan. The stream is located inside the University of Tokyo Hokkaido Forest. Many springs (top panels) occur in around the main channel (bottom panel). In this region, the mean summer water temperature of volcanic streams is 3°C colder than that of nonvolcanic streams on average. Photo credit: Yu Nagasaka. Photo 3. Wrinklehead sculpin (upper panel: Cottus nozawae) and Southern Asian Dolly Varden (lower panel: Salvelinus curilus) two major cold-water species in northern Japan. Their distribution is tightly restricted by summer water temperature. Photo credit: Yu Nagasaka (upper panel) and Chiharu Furusawa (lower panel). Photo 4. View of biotic and abiotic surveys in mountain streams, Japan. Macroinvertebrates (upper left panel) and fish (lower left panel) were collected once in each monitoring stream. Water loggers were installed with short sections of perforated PVC pipes to facilitate water exchange and shield them from sunlight (right panels). Photo credit: Jorge García Molinos. Photo 5. Dynamic changes in riverscapes at a monitoring site due to a large flood associated with Typhoon Hagibis, 2019 (before: upper panel, after: lower panel). Monitoring of water temperature in the Japanese archipelago is very challenging because of the many typhoons hitting the archipelago every summer season. Unfortunately, the temperature data of this site in 2019 was not available due to the loss of the logger. The yellow bridge at the upper-left corner of the picture offers a good visual reference to compare both pictures. Photo credit: Nobuo Ishiyama. These photographs illustrate the article “Underlying geology and climate interactively shape climate change refugia in mountain streams” by Ishiyama, N., Sueyoshi, M., García Molinos, J., Iwasaki, K., Negishi, J. N., Koizumi, I., Nagayama, S., Nagasaka, A., Nagasaka, Y. & Nakamura, F. published in Ecological Monographs. https://doi.org/10.1002/ecm.1566

Diel and seasonal changes in gut contents of omnivorous–carnivorous macroinvertebrates in the Yura River, Japan

AbstractDiel and seasonal changes in the gut contents of omnivorous–carnivorous macroinvertebrates were examined in a Japanese mountain stream based on direct observation of gut contents. Carnivorous–omnivorous (predator) macroinvertebrates were sampled at four time periods (02:00–03:00, 08:00–09:00, 14:00–15:00, and 20:00–21:00) on 3 days in each of March, June, September, and December. A total of 1391 individual macroinvertebrates belonging to 71 taxa were dissected: identifiable gut contents were observed in 928 individuals and prey identified to the family level were observed from the guts of 564 individuals. Using nonmetric multidimensional scaling, interspecific variation in foraging patterns was summarized into two axes that approximately correspond to body size and habitat preferences of prey taxa. Although seasonal patterns in the number of prey individuals in a gut varied among taxa, in March and December, several predators notably foraged on taxa such as Simuliidae, which inhabits stone surfaces in river sections with a rapid current. This pattern may be explained by season‐specific prey availability and predation risks from vertebrates. Diel changing patterns in the number of prey individuals per gut varied among predator taxa, and most predators did not show obvious proportional changes in gut contents. These results indicate that subcompartments of interaction networks and numerous indirect effects via intraguild predation potentially exist within the “guild” of macroinvertebrates, which are often summarized as mesopredators of stream food webs.

Effects of Flow Reduction on a Whitespotted Char Population in a Japanese Mountain Stream

AbstractI evaluated the effects of long‐term (about 270 d/year) and large‐volume (83.3% at mean flow) reductions in stream flow on a population of Whitespotted Char Salvelinus leucomaenis. I compared a range of biological parameters (density, biomass, condition factor, and age composition) between populations of char in the free‐flowing (above dam) and regulated (below dam) sections of a Japanese mountain stream over a 4‐year period. The density and biomass of age‐1 and older fish was significantly lower in the regulated section than in the free‐flowing section: 32.8% reduction in density and 42.5% in biomass. The mean condition factor of age‐1 and older fish was significantly lower in the regulated section. In addition, the percentage of age‐2 and older fish in the total catch was significantly lower in the regulated section. Except for flow, the physical environment was similar in both the free‐flowing and regulated sections. Thus, the changes I observed in the regulated section were likely caused by flow reduction. I hypothesize that a decrease in food availability associated with the reduction in flow caused the decrease in density and condition factor in the regulated section. I also speculate that an increase in density in the pools due to flow reduction resulted in increased aggression among conspecifics. In turn, this results in an increase in the emigration of individuals, particularly older and larger fish, in the regulated section. The decreases in the density, condition factor, and the number of older and larger fish following the reduction in flow probably explain the decrease in biomass in the regulated section.Received November 20, 2012; accepted July 15, 2013

Present status and conservation of the markless forms of stream-resident masu salmon Oncorhynchus masou (the so-called ‘iwame’) in Japanese mountain streams

As a markless form of stream-resident masu salmon (Oncorhynchus masou), the so-called ‘iwame,’ which can be distinguished from the sympatric normal form of the salmon by their plain body pattern, has been previously reported among seven local populations (A–G) in Japanese mountain streams. In the present study, all populations but B (where any information is entirely missing) were surveyed in a snorkeling survey (detection rate: 34.7%) in 2005 to elucidate the recent conditions of the markless forms. The ratios of the markless forms were 13.0% (9/69), 0.0% (0/364), 5.6% (68/1,205), 0.8% (1/132), 0.0% (0/1,181) and 64.6% (155/240) in A, C, D, E, F and G, respectively. Markless forms might indeed be already extinct in C and F where the stocking of non-native hatchery individuals has been carried out extensively. The same survey was repeated in D in 2009: the markless ratio had significantly decreased to 2.4% (19/783), although the reason for this was unknown. In D, the ratio of the markless form was higher in the mainstream as opposed to the tributaries in both 2005 and 2009, which might imply that the habitat of the markless form differs from that of the normal form.

Parasite-mediated allochthonous input: Do hairworms enhance subsidized predation of stream salmonids on crickets?

Energy and nutrients flow in diverse pathways across heterogeneous landscapes and tightly link the discrete food webs in local habitats. However, parasitism that enhances allochthonous resource input has not been previously documented. In a well-known example of parasite manipulation of host behaviour, crickets infected by mature hairworms (Nematomorpha) seek and jump into water when the worms reach the free-living stage. We found that a large number of trout (22%–61%), an aquatic predator, preyed on camel crickets (genera Diestrammena Brunner von Wattenwyl, 1888 and Tachycines Adelung, 1902) in September in five Japanese mountain streams where this host–parasite system exists. Trout (Kirikuchi charr, Salvelinus leucomaenis japonicus (Oshima, 1961); red-spotted masu salmon, Oncorhynchus masou ishikawae Jordan and McGregor, 1925) that preyed on crickets frequently ingested hairworms, whereas trout that did not prey on crickets did not ingest hairworms. Our results strongly suggest that hairworms enhance stream salmonid predation on camel crickets. This is the first documentation of parasitism enhancing allochthonous resource input in nature. Trout ingested a greater mass of crickets than other prey species in September, and this energy influx may play an important role in food-web dynamics in headwater streams.

Intergeneric Hybridization between Sympatric Kirikuchi Char and Red‐Spotted Masu Salmon in a Small Japanese Mountain Stream

AbstractHybridization occurs widely across salmonid species. Intergeneric hybridization of salmonid species in nature, however, has been rarely reported. Using microsatellite and mitochondrial DNA (mtDNA) markers, we obtained evidence of intergeneric hybridization between threatened, naturally sympatric Kirikuchi char Salvelinus leucomaenis japonicus and red‐spotted masu salmon Oncorhynchus masou ishikawae in an upper drainage of the Totsu River system, which is located on Kii Peninsula, central Honshu, Japan. Fifteen suspected hybrid juveniles were captured in August 2005 in a tributary within a surveyed drainage, where an intergeneric pair consisting of a female Kirikuchi char and a male red‐spotted masu salmon was observed during the preceding spawning season. The suspected hybrids all appeared to be F1 on the basis of microsatellite genotypes at five loci, which is consistent with the previously reported infertility of such hybrids. The maternal parent species was presumed to be the Kirikuchi char, since all hybrids had this species' mtDNA haplotype. The estimated number of hybrids was equivalent to that of age‐0 Kirikuchi char, suggesting that at least half of the annual reproduction of Kirikuchi char in the tributary was disturbed by the present hybridization. Six of nine hybrid recaptures were collected from the same tributary in 2006, indicating that hybrids could survive and stay in their nursery tributary at least until age 1. This study suggests that intergeneric hybridization negatively affects long‐term persistence of both parental species, especially Kirikuchi char, through reproductive disturbances and competition for resources.

Changes in periphyton abundance and community structure with the dispersal of a caddisfly grazer, Micrasema quadriloba

We examined the larval population densities and biomass of a caddisfly grazer, Micrasema quadriloba, and the abundance and community structures of periphyton at a segment scale (7.4 km with four study sites), along a second-to fourth-order Japanese mountain stream throughout the grazer’s life cycle. In the uppermost riffle of the study segment (site 1), periphyton abundance was kept at low levels when the larvae occurred. The larval distribution spread downstream as larvae developed from first instars in May to fifth instars in January. We performed multiple regression analyses to test the effects of environmental variables and larval biomass on periphyton abundance in both the riffle of site 1 and the study segment; the results revealed that the larval biomass was significantly negatively correlated with periphyton abundance similarly in both the riffle and the study segment. In addition, both the correlation and community analyses showed that the larval biomass was significantly negatively correlated to the relative abundance of large and/or filamentous microalgae, which appeared in the uppermost layer of the periphyton mat, and that larval biomass was significantly positively correlated to the relative abundance of small diatoms, which strongly adhered to the substrate. Thus, the present study implied that the grazing of M. quadriloba larvae would regulate the abundance of periphyton in a riffle and also regulate the abundance and community structure of periphyton at the segment scale with the expansion of their longitudinal distribution.

Conditions controlling the onset of breeding migration of the Japanese mountain stream frog, Rana sakuraii

I studied the conditions controlling the timing of breeding migration of the Japanese mountain stream frog Rana sakuraii, an explosive breeder, over 9 years (1992, 1993 and 1999-2005). I analysed two factors: the daily cumulative temperature (DCT) during hibernation and the triggering temperature on the day of migration onset. Frogs hibernated in shallow running water in streams in December. A total of 53,155 breeding migrating adults were captured by traps. Every year, breeding migration was induced by a rise in daily maximum water temperature to about 5 degrees C. However, its date was limited to 1 February at the earliest, and the onset needed a DCT (from 20 January, using 3 degrees C as the threshold for daily effective temperature) of at least about 15 degrees C. Earlier (e.g. in mid- or late January), even if the maximum temperature rose to 5-8 degrees C, migration did not begin. Moreover, even in early February, if the maximum temperature rose to 5 degrees C, if it had been too cold in January and the DCT was low, migration would not begin until mid- or late February. Thus, the earliest date of readiness for migration varied from 1 February to mid-February, depending on the winter DCT. Logistic regression analyses showed that both factors, the DCT and the daily temperature, were significant. I propose that in temperate-zone amphibian explosive breeders, both the passing of an essential number of days and an essential DCT during hibernation are prerequisites for the onset of breeding migration before the daily temperature rises to the threshold.

Effects of reach-scale canopy cover on trophic pathways of caddisfly larvae in a Japanese mountain stream

Differences in trophic pathways between reaches with and without tree canopy cover above the channel were assessed using stable isotopes in a 1.4-km stretch of the Kamo River, Japan. The trophic pathways of two larval trichopteran species, a grazer (Goera joponica, Goeridae) inhabiting stone surfaces and a net-spinning filter-feeder (Stenopsyche marmorata, Stenopsychidae) inhabiting interstices of the stony stream bottom, were estimated using carbon and nitrogen isotopes in reaches with and without canopy cover in winter. The δ13C values of G. japonica were similar to those of periphyton at each station, suggesting that G. japonica is a grazer on periphyton. A significant positive correlation between carbon isotope values of S. marmorata and benthic particulate organic matter (BPOM) indicated that BPOM varied in composition according to the amount of solar energy within a reach. In addition, there was a significant positive correlation between carbon isotope values of filter-feeders and the periphytic algal contribution to BPOM using an isotope mixing model, indicating that the main food source of the filter feeders was derived from the in situ periphytic algae in open reaches and from a terrestrial source in canopy-covered reaches.

Biotic and Abiotic Influences on Nest-hatching Outcome in the Japanese Fluvial Sculpin, Cottus pollux

I examined the interrelationships among the timing of reproduction, physical characteristics of nests and hatching outcome of male Japanese fluvial sculpin, Cottus pollux, in a Japanese mountain stream with flood disturbance. Breeding took place from mid-February to early April, with bimodal peaks of breeding activity. Male body size had a significant effect on the timing of initial reproduction and mating success. Hatching outcome, by contrast, was not affected by male body size and male mating success. The timing of flood occurrence varied between years, and most nest-hatching failure was observed within 1 week after floods. Failed nests were exposed to faster current velocity than successful nests, and degree-days of failed nests negatively correlated with the magnitude of flood flow experienced. These data suggest that the timing and magnitude of floods substantially affected hatching outcome of the species. I also discuss the adaptive significance of bimodal breeding activity of males from life-history perspective in the face of variable stream flow conditions.

Reach-Scale Distribution Dynamics of a Grazing Stream Insect, Micrasema quadriloba Martynov (Brachycentridae, Trichoptera), in Relation to Current Velocity and Periphyton Abundance

Reach-scale temporal shifts in the distribution of larvae of a grazing caddisfly, Micrasema quadriloba (Brachycentridae), were investigated in a Japanese mountain stream. The larvae showed an aggregated distribution within the reach at the beginning of the immigration, then became randomly dispersed throughout the reach as the immigration progressed. The abundance of periphyton in the reach decreased dramatically with increasing dispersal of the larvae. Simple regression analyses revealed that the stream's flow regime was the most important environmental factor that determined the reach-scale distribution of the larvae and that the relationship between the flow regime and the distribution of the larvae shifted temporally. In addition, our results suggest that only this species of grazing insect, which was dominant in the study reach, controlled the reach-scale abundance of the periphyton.

Effects of a Severe Flood on the Movements of Japanese Fluvial Sculpin

I studied the movements of adult Japanese fluvial sculpin, Cottus pollux, in a Japanese mountain stream. An exceptionally severe flood in late September had negative impacts on refuge abundance, condition and population density of the sculpin. The mean distance moved monthly correlated positively with water discharge, but not with water temperature or with population density. Overall, the mean distance sculpins moved after the flood was significantly greater than before the flood, and sculpins tended to move into riffle-raceways after the flood. Comparisons of refuge-site limitation for adults and water depths between habitats indicated that the flood affected riffle-raceways less than pools. Fish in poorer conditions were likely to move extensively, and the condition of fish captured initially in pools deteriorated more significantly than that of sculpins captured in riffle-raceways. Movement bias into riffle-raceways by the sculpins after the flood suggests they sought suitable habitat with available refuges. The results suggest vulnerability to flood disturbance of the sculpins inhabiting the interstitial spaces of the substrate.

Food habit divergence between white-spotted charr and masu salmon in Japanese mountain streams: circumstantial evidence for competition

The diet and foraging microhabitat of white-spotted charr, Salvelinus leucomaenis, were compared between mountain stream reaches where it occurs with (sympatric) and without (allopatric) masu salmon, Oncorhynchus masou masou, a potential competitor, to examine the evidence for interspecific competition between these fish, which commonly co-occur in Japanese mountain streams. In three streams examined, the similarity between the diets of allopatric charr and salmon was much greater than that between the diets of sympatric charr and salmon. Both allopatric charr and sympatric salmon intensively utilized terrestrial invertebrates among stream drifts (52%–65% of the diet), whereas this prey category made up only an intermediate portion of sympatric charr diets (11%–29%). Examination of available prey composition in stream drifts showed that the consumption of terrestrial invertebrates by allopatric charr and sympatric salmon was approximately twice as much as that by sympatric charr. The presence of salmon, a potential competitor, may alter the diet of charr in the sympatric reaches. Charr holding focal points closer to the streambed were considered less efficient than sympatric salmon in their utilization of terrestrial invertebrates drifting primarily on the stream surface, although the foraging microhabitat of the charr was not influenced by the salmon. The mechanisms responsible for the dietary divergence between sympatric charr and salmon are probably the consequence of scramble competition over terrestrial invertebrates drifting on the stream surface.

Residency and movement of stream‐dwelling Japanese charr, Salvelinus leucomaenis, in a central Japanese mountain stream

Abstract – The residency and movement of stream‐dwelling adult (2+ and older) Japanese charr, Salvelinus leucomaenis, were studied by mark and recapture experiments in the Jadani Stream, a headwater tributary of the Tedori River, central Japan, from 1986 to 1989. Of the marked fish, 31.3–58.3% were recaptured in the same pools where they had been caught during the study periods of summer (June–August), autumn (August–November) and winter–spring (November to the next June) and no seasonal movement was observed. The mean distances that the fish moved during the study periods ranged from 139.0 to 502.3 m and many movements longer than 1000 m were observed. Between the resident and the moved fish, there was little difference in body length, growth rate or sex. For the fish that had been resident in the same pools and riffles at previous recaptures, most fish were recaptures in the same locations at the next recapture. Conversely, for the fish that moved previously, most fish were recaptured in different locations from previous sites at the next recapture. These results suggest that Japanese charr exhibit relatively high residency throughout the year, but many fish moved longer distance. The results also suggest the presence of static and mobile components in the charr population.

Population viability of stream-resident salmonids after habitat fragmentation: a case study with white-spotted charr ( Salvelinus leucomaenis) by an individual based model

Throughout the world, rivers are increasingly fragmented by artificial barriers, such as damming and road crossing. In Japanese mountain streams, most populations of white-spotted charr, a salmonid fish, are highly fragmented by numerous small dams. Most of these dams were constructed after 1970. In this study, we conducted a population viability analysis of fragmented white-spotted charr populations using a simple individual based model. The constructed model is age-structured and density dependent that incorporates both demographic and environmental stochasticity. The probability of population persistence decreased substantially between after 30 years and after 100 years, especially for populations having a small carrying capacity. Even though white-spotted charr occupies many fragmented habitats now, our results suggest small fragmented populations are not viable. A sensitivity analysis showed that adult survival, not juvenile survival and egg number, was the most important criterion for the prospects of population persistence. Installations of efficient fish ladders or dam removal are necessary as soon as possible to restore dammed-off populations.

Space use by the Japanese fluvial sculpin, Cottus pollux, related to spatio-temporal limitations in nest resources

Space use by the Japanese fluvial sculpin, Cottus pollux, as related to nest availability was studied in a Japanese mountain stream. Males had larger home ranges than females before breeding. A measure of nest resource limitation was L < 1 and the same nest rock was used by two males successively in three cases, indicating a limited supply of suitable nest rocks for males. All males included the nest rocks in their home ranges, but the timing of nest occupation was apparently dependent on male size, suggesting the presence of male-male competition for the nest rocks. Females, on the other hand, exhibited two different patterns in space use, independent of body size: (1) they spawned in their home ranges, or (2) they spawned out of their home ranges and returned. Nest cavity area did not affect male reproductive success. Spatial separation between female home ranges and nest location was the main reason for the females' movement out of their home ranges. The limitation in the male mating phase (5.7 days on average) might also have forced the females to move out of their home range to spawn. The reason behind such temporal limitation in the male mating interval was discussed from the viewpoint of the energy cost accompanying male parental care.

Flexible niche partitioning via a foraging mode shift: a proposed mechanism for coexistence in stream‐dwelling charrs

Summary1. Foraging behaviour, diet and interference competition were examined for two morphologically similar charrs,Salvelinus malma(Dolly Varden) andS. leucomaenis(white‐spotted charr), under varying food resource conditions over four summers in a Japanese mountain stream. Data were used to test predictions from a mechanistic model of resource partitioning developed from an earlier field experiment.2. The charrs adopted one of two distinct foraging modes, ambushing drifting invertebrates from relatively fixed foraging positions or actively searching for benthic prey over large areas. The proportion of benthos foragers increased markedly when drifting prey declined, and was much greater inS. malmathanS. leucomaeniswhen drift was lean, upholding predictions made from our earlier experiment.3. For drift foragers of both species, frequency of foraging attempts decreased as drift rate declined, and aggressive encounters increased. In contrast, for benthos foragers of both species the frequency of foraging attempts was essentially constant across the range of benthos biomass measured, and aggressive encounters remained low.4. Salvelinus leucomaenisate larger drifting prey thanS. malma, even though the former charr were smaller. In contrast,S. malmaforaged on benthic prey at a higher rate thanS. leucomaenis, although there was no difference in prey mass. Thus, the optimal point to shift to benthic foraging is at a higher drift threshold forS. malmathanS. leucomaenis, most probably due to differences in jaw morphology. Moreover, because dominance for favourable drift foraging positions was based on size alone,S. malmashifted to benthos foraging at a larger size thanS. leucomaenis, as predicted by a simple model.5. Charr consumed distinct prey types according to their foraging mode. Drift foragers primarily ate terrestrial invertebrates, whereas benthos foragers ate mainly chironomid larvae. Consequently, diet overlap was high when drift was abundant and both species were drift foragers, but declined as drift declined andS. malmashifted to benthos foraging. Therefore, species‐specific differences in foraging mode shifts across the resource gradient explained the flexible resource partitioning we observed, and probably account for the coexistence of these congeneric charrs in zones of sympatry in northern Japan.

Embryonic and larval development of a Japanese spinous loach,Cobitis takatsuensis

The embryonic and larval development ofCobitis takatsuensis, a mountain stream spinous loach, was surveyed by incubating artificially inseminated eggs. The mean diameter of the inflated eggs and mean total length of newly-hatched larvae were 2.7 mm and 5.7 mm, respectively. The eggs were spherical, transparent and unpigmented, with a pale yellow yolk and no oil globule. The daily cumulative temperature to hatching was estimated to be 70–110°C. day. Hatched larvae were unpigmented with outer gill filaments on their cheeks, as in otherCobitis species, but the melanophores were comparatively less obvious at each developmental stage. The larvae started feeding eleven days after hatching yolk absorption being completed sixteen days after hatching. All the fin rays were fully developed and the juvenile stage reached at 16 mm TL, 38 days after hatching. Embryonic and larval developmental traits ofC. takatsuensis, such as egg size, clutch size and larval pigmentation, were similar to the Korean species,Niwaella multifasciata, that lives in the upper reaches of the Nak-tong river, andN. delicata, which inhabits Japanese mountain streams, rather than to its congeners. Among cobitine fishes, the spawning of a small number of larger eggs yielding larger larvae without pigmentation, characteristics shared byC. takatsuensis, N. multifasciata andN. delicata, is attributable to adaptation to cold mountain streams.