Seasonal distribution of adult crucian carp nigorobuna <Emphasis Type="Italic">Carassius auratus grandoculis</Emphasis> and gengoroubuna <Emphasis Type="Italic">Carassius cuvieri</Emphasis> in Lake Biwa,Japan

Seasonal habitat use by nigorobuna Carassius auratus grandoculis Temminck et Schlegel and gengoroubuna Carassius cuvieri (Temminck et Schlegel) in Lake Biwa was investigated using acoustic telemetry. Twenty-three nigorobuna and 11 gengoroubuna specimens caught using set-nets in the lake’s south basin were surgically fitted with acoustic transmitters and then released. Signals from the fishes were recorded by 23 receivers installed around the lake. Between April and June 2007, the first spawning season after release, signals were received from all tagged fishes. Thereafter, until the second spawning season, signals were collected from 26 and 45% of released nigorobuna and gengoroubuna individuals, respectively. Seasonal habitat preferences for these species were studied by distance-based analysis. The analysis revealed that nigorobuna tended to stay near their spawning area in the south basin of the lake throughout the year, whilst gengoroubuna tended to show a seasonal migration pattern between the north and south basins. After the spawning season, the latter species migrated to the north basin where it remained until the next spawning season, when it returned to the south basin. This is the first report of seasonal migration of nigorobuna and gengoroubuna in Lake Biwa.     

Body-length frequency and spatial segregation of the North Pacific spiny dogfish <Emphasis Type="Italic">Squalus suckleyi</Emphasis> in Tsugaru Strait,northern Japan

The present study elucidated the length structure and habitat segregation of North Pacific spiny dogfish (SPD) Squalus suckleyi in the Tsugaru Strait of northern Japan. Length–frequency distributions using kernel density estimation were determined for SPD captured by the bottom longline fishery landed at Minmaya from 1999 to 2011 and at Ohma from 2007 to 2011. Length–frequency distributions significantly differed between landings at the two ports; SPD at Minmaya were on average larger (65–85 cm precaudal length: PCL) than at Ohma (55–75 cm PCL). This difference is evidence of the length-based spatial segregation of the SPD. The seasonal landing pattern of the SPD was also different between the two ports. The SPD landed at Minmaya were largest during February–June and SPD < 75 cm PCL were caught at Ohma throughout the year. This different landing pattern was related to seasonal differences in bottom-layer water temperatures between the two fishing grounds. Females were thought to be dominant at Minmaya, whereas males dominated in most of the catches at Ohma. These results suggest spatial patterns of sexual segregation for this species in the Tsugaru Strait and require elucidation of the SPD stock condition at Minmaya and Ohma.     

Increasing nitrate removal at low temperatures by incorporating organic matter into paddy fields

Denitrification of paddy fields is a key process for improving water quality in fields where nitrate concentrations are high. The objective of the present study was to understand the effects of incorporating organic carbon (C) into soil on the denitrification rate of paddy fields in winter. On 11 December 2007, separate paddy field plots were prepared by incorporating 5 Mg ha⁻¹ of rice straw (RS), 11 Mg ha⁻¹ of rice straw compost (RSC) or a control. A field with a high concentration of nitrate in the water (averaging 18 mg N L⁻¹) was irrigated until 29 March. During the experiment, the daily average soil temperature at a depth of 0.05 m ranged between 3 and 15°C. The nitrate concentration in the surface water in the RS plot, where the residence time was 2 days, decreased more than the concentration in the control or RSC plots. The total estimated nitrate removal from each plot in relation to the other plots was RS > RSC = control. Measurements of the soil from each plot on 29 February 2008 showed that incorporation of RS significantly increased the denitrification potential, even at low temperatures (5–10°C). Furthermore, the RS plot contained more dissolved organic C than the control or RSC plots. This result indicates that supplying RS effectively increases denitrification under low-temperature conditions.     

Feeding habits of mesopelagic fish <Emphasis Type="Italic">Lampanyctus jordani</Emphasis> (Family: Myctophidae) over the continental slope off Tohoku area,northern Japan

ABSTRACT:   The feeding habits of Lampanyctus jordani , an abundant mesopelagic fish in the subarctic North Pacific, was examined based on the stomach contents of 721 specimens collected over the continental slope off the Tohoku area, Pacific coast of northern Japan during April and October from 1996 to 1998. The prey items comprised mainly crustaceans such as copepods, amphipods, euphausiids and decapods. Euphausiids were the most important items in the diet both during April and October. During April, when the annual maximum of zooplankton biomass occurred and the Oyashio Intrusion Current prevailed, L. jordani fed intensively and consumed a high proportion of Euphausia pacifica . These seasonal variations also influenced the feeding intensity and dietary diversity. Feeding intensity, measured by the stomach contents index, was higher during April than October, reflecting the higher biomass of zooplankton in the Tohoku area during spring. The dietary diversity of L. jordani was lower during April than October, indicating that L. jordani shifted to a wider variety of prey when the availability of E. pacifica was limited.     

Development of a technique to estimate the horizontal distribution of lit fishing vessels in the East China Sea using satellite luminescence

Fisheries Science - The East China Sea is a semi-enclosed sea, surrounded by Japan, China, South Korea and Taiwan, and is continuously influenced by lit fishing vessels overexploiting fishery...     

Ecological studies on subtropical evergreen broad-leaved forest in Okinawa, Japan: Litter production and nutrient input

Patterns of litterfall and nutrient input in a subtropical evergreen broad-leaved forest in northern Okinawa, Japan, were studied during May, 1996–April, 1999. The mean annual rate of litterfall in the five sampling plots ranged from 6.84 to 8.93 Mg ha⁻¹ yr⁻¹, of which 63.3–68.5% were leaves; 22.4–29.1% woody parts (including branches < 5.0 cm in diameter and bark); 2.8–5.0% sexual organs and 4.6–6.3% miscellaneous material. Significant differences were found among plots and among years. Significantly monthly differences pronounced seasonal patterns in litterfall were observed. Total litterfall and leaf litter showed negative correlations with relative basal area of the dominant species,Castanopsis sieboldii; and showed positive correlations with mean height of the stands. The dominant species,C. sieboldii produced an average of 2.36 Mg ha⁻¹ yr⁻¹ of leaf litter, which covered 30.5% of the annual litter production, and the nutrient input from those litterfall contributed 32.3, 28.3, 30.2, 22.2, 32.5, and 30.5% of total N, P, K, Ca, Mg, and Na, respectively. Nutrient use efficiency in litter production was high, especially for P and K compared with other broad-leaved forests in Japan indicating that P and K may be limiting in Okinawan evergreen broad-leaved forest.     

Hepatic disposition of parathion: Uptake by isolated hepatocytes and chromatographic translobular migration

Isolated rat hepatocytes suspended in Waymouth's medium absorbed parathion rapidly and reversibly until the intracellular parathion concentration reached more than 300 times the ambient concentration. The distribution quotient q, defined as the ratio of intra- and extracellular concentrations at equilibrium, decreased when horse serum was added to the medium. The high hepatocyte affinity and rapid uptake of parathion suggested that this compound might be almost completely absorbed by periportal hepatocytes in the perfused liver and migrate downstream chromatographically through the lobule. Parathion infusion experiments verified this prediction and showed that the migration rate is dependent on the q value. The chromatographic feature may be useful as a basis for nonhistological investigation of intralobular hepatocyte heterogeneity. The lobule may function as a reverse-phase chromatograph also for many other unionized xenobiotics. Implications of the findings in the hepatic disposition of xenobiotics in vivo are discussed.     

Significance of phosphorylation in organophosphate-mediated β-glucuronidase release from the rat liver

The elevation of rat blood β-glucuronidase caused in vivo by O,O-dialkyl O-phenyl phosphates and phosphorothioates correlated well with the electron-withdrawing tendency (σ^?) of leaving group substituents indicating the importance of a phosphorylation mechanism in the enzyme release. Hydrophobic bonding of these compounds may facilitate the phosphorylation since hydrophobicity (π) of substituents also correlated with the enzyme release. SKF 525-A decreased the elevation of β-glucuronidase by parathion through the suppression of paraoxon production. Pretreatment of rats with phenobarbital or DDE resulted in lower and delayed enzyme release caused by parathion.     

Genetic diversity of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">spinaciae</Emphasis> in Japan based on phylogenetic analyses of rDNA-IGS and <Emphasis Type="Italic">MAT1</Emphasis> sequences

Twenty-eight isolates of Fusarium oxysporum f. sp. spinaciae (FOS; the causal agent of spinach wilt) collected from Japan were assessed for mating type and subjected to phylogenetic analysis. Mating type analysis revealed all isolates to be MAT1-2, suggesting that there is no sexual recombination within the population. Phylogenetic analyses based on nucleotide sequences of the ribosomal DNA intergenic spacer (IGS) and the mating type locus (MAT1) suggested that FOS is polyphyletic. The cluster analysis based on IGS showed four phylogenetic groups (S1–S4) among the isolates. Two distinct lineages, S1 and S3, included FOS isolates both of the vegetative compatibility group (VCG) types, 0330 and 0331, demonstrating that VCG differentiation in FOS may not necessarily reflect the phylogenetic relationships based on IGS and MAT1-2-1.     

A simple method for a mini-preparation of fungal DNA

A simple method was established to prepare DNA from fungal mycelia cultured on an agar plate. The fungi tested successfully with this method contained Zygomycetes, Ascomycetes, Basidiomycetes, and Oomycetes. This method did not require any time-consuming steps to crush or digest mycelia or fractionation in a phenol–chloroform mixture. The DNA was easily extracted by immersing and dispersing the mycelial plugs in a specific buffer (200 mM Tris-HCl, 50 mM ethylenediaminetetraacetic acid, 200 mM NaCl, 1% n-lauroylsarcosine, pH 8.0), then concentrated by ethanol precipitation. The total time to complete the whole procedure was less than 1 h. The quality and quantity were sufficient for polymerase chain reaction amplification and Southern blot analysis.