Temporal and spatial distributions of Biwa salmon Oncorhynchus masou subsp. by ultrasonic telemetry in Lake Biwa,Japan

Biwa salmon Oncorhynchus masou subsp. were tagged with ultrasonic transmitters and released in Lake Biwa, Japan. The temporal and spatial distributions were investigated by using two types of ultrasonic telemetry system, active tracking and passive monitoring. Biwa salmon cruised throughout the north basin horizontally and were distributed from the surface to the bottom vertically in the lake. An individual monitored for over 1 year showed the diurnal patterns of vertical distribution and the seasonal patterns of horizontal distribution. The vertical distribution of the fish during daytime in the stratified period was bimodal, suggesting a feeding strategy targeting both fish near the thermocline and the amphipods near the bottom. During the night, however, the fish maintained a fixed depth range. The fish were distributed over a wider horizontal area in the mixed period than in the stratified period. Three individuals swam in shallower water and experienced higher water temperatures during the spawning season than before moving between offshore and coastal areas.     

Variation in agonistic encounters in a dominance hierarchy of freely interacting red-spotted masu salmon (Oncorhynchus masou ishikawai)

Abstract– Agonistic behaviour and dominance relationships in red-spotted masu salmon, Oncorhynchus masou ishikawai , were observed in a mountain stream pool. A linear, size-structured dominance hierarchy was recognized among individuals, body weight being a more important determinant of dominance status than fish length. Immigrant fish interacted more frequently with residents of similar body size than with larger or smaller fish during the early period following immigration. Thereafter, frequency of interactions rapidly decreased. When a fish was attacked, it reacted in a variety of ways in close accordance with its opponent's dominance rank: responses were to simply flee, flee with lateral display, revolt by performing a counter display or ignore the aggression. Such behavioural modification seems to be established during the successive agonistic encounters, in particular, early encounter periods when frequent interactions took place.     

White muscle of masu salmon,Oncorhynchus masou masou,smolts possesses a strong buffering capacity due to a high level of anserine

Masu salmon, Oncorhynchus masou masou, fry were fed with diets containing three different levels of protein for 18 weeks, and the levels of free amino acids and related compounds in the white muscle were compared among the dietary groups and between smolts and parr. The anserine level in the white muscle of smolts was always higher than that of parr, while histidine and glycine levels in the former were always lower than those in the latter, irrespective of dietary treatments. A mixed solution of crystalline anserine, histidine and glycine simulating these amino acid levels in the white muscle of the smolts had a stronger buffering capacity in the physiological pH range than that simulating those levels present in parr. These results suggest that even in freshwater conditions, the white muscle of smolts possesses a more potent buffering capacity than the muscle of parr, for anaerobic burst swimming during the downstream migration. Moreover, the white muscle of smolts fed the high-protein diet had a significantly higher level of anserine than that of smolts fed the low- or intermediate-protein diets, and the solution mimicking the white muscle of smolts fed the high-protein diet showed the strongest buffering capacity among the mixed solutions tested. Thus, a diet with high-protein level could improve qualities of smolts.     

Microsatellite variation reveals fine-scale genetic structure of masu salmon, Oncorhynchus masou, within the Atsuta River

Abstract –  To describe in detail the population genetic structure of masu salmon Oncorhynchus masou , seven anadromous populations in the Atsuta River were investigated by analysis of eight polymorphic microsatellite loci. Exact test and genetic differentiation ( F _ST) revealed that significant differentiation was observed at the within-river scale. Principal components analysis revealed that the spatial pattern of genetic composition was related to geographical location of each population. Furthermore, a significant correlation was observed between genetic differentiation and geographical distance, indicating that dispersal is less likely to occur between distant populations. The results of this study imply that masu salmon have potential to show clear genetic structure at the microgeographical scale (21 km) due to precise homing behaviour.     

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.     

Serum thyroxine,estradiol-17β, and testosterone profiles during the parr-smolt transformation of masu salmon,Oncorhynchus masou

Changes in serum thyroxine (T₄), estradiol-17β (E₂) and testosterone (T) levels during the parr-smolt transformation (smoltification) were investigated in the masu salmon (Oncorhynchus masou) in 1985 and 1987. T₄ showed a peak in levels at the early stage of smoltification and E₂ and T levels peaked almost at the same time. There were no significant differences between the concentrations of serum hormones in female and males. During smoltification, germ cells in the peri-nucleolus and spermatogonia stage were present in the ovary and testis, respectively. These results suggest that E₂ and T may be involved in smoltification in the masu salmon.     

Commercial harvest of hatchery-reared masu salmon Oncorhynchus masou estimated by a coast-wide sampling program in Hokkaido, northern Japan, and the two-stage sampling schemes of landings

SUMMARY: This paper evaluates the stocking effectiveness of masu salmon Oncorhynchus masou in Hokkaido, northern Japan, through a coast-wide two-stage sampling survey of commercial landings. From January to June 1994–1996, commercial landings of masu salmon at 33–36 fish markets were sampled at 7–10 days intervals, and 60 866–72 124 fish were examined for marks indicated by fin clips. Based on the survey data, numbers of total and hatchery-reared masu salmon landed were estimated. To examine the structure of the errors, stratification of fish markets was implemented on the basis of geography and magnitudes of landings, and the stratification improved accuracy and precision of the estimates. Accuracy of the estimated numbers of total fish was evaluated by being compared to the true numbers of masu salmon landings reported by fishermen's cooperative associations. Estimates of total masu salmon landings were within ± 10% of the true numbers. The estimated recovery rates (± SE) for hatchery-reared masu salmon smolts were variable ranging from 0.18 (± 0.06) to 3.50 (± 0.41)% among the stocked groups. An optimal sampling strategy was examined to obtain precise estimates for future studies.     

Spawning behaviour of amemasu charr,Salvelinus leucomaenis leucomaenis,with a discussion of the macroevolutionary patterns of postspawning behaviour in the Salmoninae

Abstract – Video cameras inside underwater housings were used to record the spawning behaviour of a subspecies of the white‐spotted charr, the amemasu charr (Salvelinus leucomaenis leucomaenis) in the Tokimae and Onbetsu Rivers, Hokkaido, Japan. Unlike other Salvelinus species, in which females use lateral swings of their bodies to ventilate and distribute eggs over gravel crevices (undulating) immediately after spawning, female amemasu charr covered their eggs with beats of their tails (cover digging). Cover digging right after spawning has previously been documented in Salmo, Oncorhynchus and Parahucho. Phylogenetic analysis of postspawning behaviours in the Salmoninae indicated that (i) resting then covering the eggs is plesiomorphic for the group, (ii) undulating replaced resting in the ancestor of Salvelinus, (iii) cover digging was advanced in the behavioural sequence to occur immediately after egg deposition in the ancestor of Parahucho + Salmo + Oncorhynchus and in the amemasu.     

Effects of cortisol and angiotensin II on the number and size of juxtaglomerular cells in masu salmon, Oncorhynchus masou

The authors previously reported that the number and size of juxtaglomerular cells (JGCs) in the kidney increased during smoltification in masu salmon, Oncorhynchus masou. In the present study, the effects of cortisol and/or angiotensin (Ang) II ([Asn¹, Val⁵]-Ang II) on the JGC number and size in masu salmon were examined to elucidate hormonal regulation of the changes in the JGC number and size during smoltification. These hormones were injected intraperitoneally every 2 days for a total of 6 injections. There was a significant increase in the JGC number and size with time following the start of the experiment in cortisol- and cortisol + Ang II-treated groups and no significant change in control and Ang II-treated groups. On both days 5 and 11, the JGC number and size in the cortisol-treated group were significantly large compared to those of control and Ang II-treated groups, respectively. The JGC number and size in the cortisol + Ang II-treated group were significantly large compared to those of control on both days 5 and 11, and those of the Ang II-treated group only on day 11, respectively. On the other hand, there was no significant difference in the JGC number and size between the Ang II-treated and control groups and between the cortisol- and cortisol + Ang II-treated groups during the experiment, respectively. The means of the JGC number and size in cortisol-treated group on day 11 were close to those previously reported in smolt. These results suggest that cortisol induces an increase in JGC number and size during smoltification in masu salmon. This revised version was published online in August 2006 with corrections to the Cover Date.     

Movement of the fluvial form of masu salmon, <Emphasis Type="Italic">Oncorhynchus masou masou</Emphasis>, in a mountain stream in Kyushu,Japan

Using mark-recapture methods, the movements of the fluvial form of masu salmon (Oncorhynchus masou masou) in a mountain stream on the island of Kyushu, Japan, were studied. Most (78%) of the masu salmon were recaptured in the pool in which they had been originally caught and tagged. Of those that moved between pools, the proportion of individuals that moved during the breeding period was not significantly higher than the proportion that moved during the non-breeding period. However, during the breeding period, a higher proportion of larger salmon moved than did smaller fish. The proportion of mobile large males during breeding period was higher than that for small males. Also, it was found that a few individuals showed long-range movement in the autumn. As a long-term movement, 78 individual fish (65%) that were recaptured more than three times showed high sedentary tendencies. Sixteen individual mobile fish (13%) moved and returned to the original pool. Fluvial form of masu salmon in Kyushu show a high sedentary nature; however, large mature males seem to actively move in search of female during breeding period.     

Changes in levels of GnRH in the brain and pituitary and GTH in the pituitary in male masu salmon,Oncorhynchus masou,from hatching to maturation

Levels of two types of gonadotropin-releasing hormone (salmon GnRH and chicken GnRH-II) in the brain and pituitary, and content of gonadotropin (GTHIβ and IIβ) in the pituitary were measured in male masu salmon from hatching to gonadal maturation for three years in order to clarify the involvement of GnRHs in precocious maturation. Underyearling precocious males were distinguishable in summer of year 1 and were marked by an increased GSI. Spermiation was observed among these individuals thereafter every autumn. Pituitary GTHIβ content in both precocious and immature males, and GTHIIβ content in precocious males showed seasonal fluctuations — high in autumn and low in winter. Pituitary GTHIIβ content was low in immature males. Pituitary sGnRH content in precocious males increased from spring to autumn during the three-year period. sGnRH concentrations in discrete brain areas showed seasonal changes — high during autumn to winter and low in summer. Concentrations in the olfactory bulbs and hypothalamus increased significantly in association with testicular maturation during year 3. sGnRH concentrations in the hypothalamus were significantly higher in precocious males than in immature males; this was possibly due to positive feedback of steroid hormones. cGnRH-II was undetectable in the pituitary and no distinct changes were observed in its concentration in the brain in relation to maturation. The phenomenon of underyearling precocious maturation is considered to be triggered before the onset of early summer. It is suggested that males which mature precociously are larger in size and contain much sGnRH in the pituitary before the outward signs of precocity appear; sGnRH may stimulate GTH II synthesis and induce precocious maturation.     

Effects of increasing concentrations of fine suspended sediment on the survival,growth, condition factor and gill condition of artificially reared juveniles of Oncorhynchus masou,Salvelinus leucomaenis and Plecoglossus altivelis

Little is known about the effect of chronic turbidity created by fine suspended sediment on the health and growth of artificially reared Oncorhynchus masou, Salvelinus leucomaenis and Plecoglossus altivelis—three important aquaculture species in Japan. This study compared survival rate, daily growth rate, condition factor (estimated from the ratio of standard length to weight) and gill condition among like‐sized juveniles exposed to fine suspended sediment (<2‐µm fraction) at concentrations of 0, 50, 100 and 500 mg/L, after 21 days. Even at 500 mg/L, there was almost no damage to the gill condition in all species. In O. masou, the daily growth rate was unexpectedly high in the 500‐mg/L treatment group, and condition factor was higher at sediment concentrations of 100 and 500 mg/L than at 0 mg/L. In S. leucomaenis, daily growth rate was significantly lower in the 500‐mg/L treatment group as compared with all other groups, but condition factor did not significantly differ among the treatments. The survival rates of O. masou and S. leucomaenis did not significantly differ among the treatment groups. In P. altivelis, neither survival rate, daily growth rate nor condition factor significantly differed among the treatments. The concentration of fine suspended sediment that affects the growth and condition factor of each of these species is likely related to their natural habitat.     

Effects of instream structures on Kirikuchi charr, southernmost population of genus Salvelinus, in a small mountain stream of Japan

ABSTRACT:   The changes in physical habitats and responses of fish, e.g. the Kirikuchi charr Salvelinus leucomaenis japonicus , were examined by placing instream structures in a stream on the upper drainage of the Totsu River system of the Kii Peninsula, Japan, over a two-year period. Instream structures created pools below the structures, and these pools have maintained their functions as fish habitats over two years. In two treatment sections, sections A and B (some red-spotted masu salmon were removed in advance in section B), mean water depth increased soon after placing the structures, but decreased over two years. Mean water velocity slowed after placing the structures in both sections. Total fish abundance has been relatively high at the two treatment sections compared with a control section after placing the structures. Age 1 Kirikuchi charr, however, increased only in section B. These results indicate that instream structures can serve as habitat enhancement for fish, including Kirikuchi charr, in the study area if other appropriate habitat factors for respective species are taken into consideration.     

Detection of thyroid hormone receptors in the olfactory system and brain of wild masu salmon,Oncorhynchus masou (Brevoort), during smolting by in vitro autoradiography

Thyroid hormone regulates a number of physiological functions during smolting in salmonids. However, the target sites and roles of thyroid hormone in the central nervous system (CNS) are not known in detail. We detected thyroid hormone-specific binding sites (i.e. thyroid hormone receptors) in the olfactory epithelium and the brain (the olfactory bulb, the telencephalon, the mid-brain and the cerebellum) of wild masu salmon, Oncor- hynchus masou (Brevoort), during smolting by means of in vitro autoradiography with frozen sections. A saturation experiment with the brain indicated the presence of a single class of binding sites of high affinity. T3-specific binding was detected in the olfactory epithelium and in all regions of the brain except the olfactory bulb. The T3-specific binding value in the olfactory epithelium was higher than in all other regions of the brain. This binding value in the olfactory epithelium increased at the full-smolt stage. The presence of thyroid hormone receptors in various regions of the CNS suggests that thyroid hormone plays an important role in the functional change in the brain and the olfactory epithelium during smolting.     

Differences in longitudinal distribution patterns along a Honshu stream of brown trout <Emphasis Type="Italic">Salmo trutta</Emphasis>, white-spotted charr <Emphasis Type="Italic">Salvelinus leucomaenis</Emphasis> and masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis>

Brown trout Salmo trutta were first introduced into Japan in 1892, and they currently naturally reproduce in several rivers in Honshu and Hokkaido, Japan. Although negative impacts of brown trout introductions on native salmonid fishes have been documented in some Hokkaido rivers, studies of ecological interactions between brown trout and native salmonid fishes on Honshu are limited. In this study, we describe the longitudinal distribution patterns of introduced brown trout, white-spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou in a 4 km stretch of a stream in central Honshu. Underwater observations were conducted in all pools within upstream, middle and downstream sections (190–400 m in length) of this stretch in order to estimate the densities of these species. Only white-spotted charr was observed in the upstream section, while brown trout and masu salmon were observed in the middle and downstream sections. Masu salmon densities, however, were much lower than brown trout densities. In the downstream section, white-spotted charr was absent. These results are consistent with results from previous studies of Hokkaido rivers, where it was found that white-spotted charr in low-gradient areas tend to be displaced by brown trout.     

Detection of hybrids between masu salmon <Emphasis Type="Italic">Oncorhynchus masou masou</Emphasis> and amago salmon <Emphasis Type="Italic">O. m. ishikawae</Emphasis> occurred in the Jinzu River using a random amplified polymorphic DNA technique

Identification of masu salmon Oncorhynchus masou masou and amago salmon O. m. ishikawae was accomplished using a random amplified polymorphic DNA (RAPD) technique. Of 80 primers screened, three primers amplified subspecies-specific fragments (OPA11-1095 ^*, OPB5-1618^* and OPD5-2038 ^*). Based on fragment patterns, 33 hybrids were detected among 150 upstream-migrating individuals in the Jinzu River, central Japan, a long-time habitat of masu salmon, to which amago salmon were recently introduced. All of the individuals examined in the 2000–2002 cohorts were identified as F ₁ and F _x as well as pure masu and amago forms. These results indicated continuing hybridization, the genetic pollution of the native masu salmon population by amago salmon possibly being a serious problem in the Jinzu River. Both standard length and body weight in F ₁ hybrids tended to be less than in pure masu salmon. However, F _x hybrids showed similar body sizes to masu salmon.