Interannual variability in stock abundance of the neon flying squid, Ommastrephes bartramii, in the North Pacific Ocean during 1979–1998: impact of driftnet fishing and oceanographic conditions

Variability in catch-per-unit-effort (CPUE) was examined for the autumn cohort of Ommastrephes bartramii collected with research driftnets during 1979–1998 along five longitudinal transects passing through the Subarctic, Transitional and Subtropical Domains in the North Pacific. CPUE was generally low during the period of intensive commercial driftnet fishing (1980–1992) and increased following the 1992 moratorium on the use of large-scale driftnets. However, CPUE levels were low for the cohorts hatched in 1992 and 1996 (captured in subsequent years owing to a one-year life of O. bartramii ) that experienced low sea surface temperatures from hatching to recruitment. Among similar-aged squid collected from 180° and 179°30'W in June, mantle lengths were significantly greater in 1997 than during 1995–96. These findings suggest that the driftnet fishery and sea surface temperatures from hatching to recruitment strongly affected stock abundance and possibly growth.     

Squamous cell carcinoma in a digit of the hind limb with systemic metastasis in a 17-year-old female koala

We encountered a case of cutaneous squamous cell carcinoma (SCC) in a 17-year-old female koala at a zoo. A fragile, papillary, elevated mass was found on the third digit of the right hind limb. SCC was identified histopathologically: squamous cell-like polygonal tumor cells showed a nest-like growth pattern with epidermal down growth, central keratinization and necrotic foci, and invaded dermal connective tissues. Metastatic lesions were observed in various organs, including the lung and axillary lymph node: in the lung, multiple metastatic foci similar to the primary lesion, and in the axillary lymph node, individual polygonal tumor cells infiltrated the sinusoids. Immunohistochemistry revealed that the tumor cells were positive for proliferating cell nuclear antigen, which exhibited 32–33% of labeling indices in the tumor cells. To our knowledge, this is the first report of a case of SCC in a digit of a koala.     

Biotic and abiotic processes of nitrogen immobilization in the soil-residue interface

The interface between decaying plant residues and soil is a hotspot for microbial immobilization of soil inorganic N. Recent studies on forest and grassland soils have demonstrated that rapid abiotic immobilization of inorganic N is also induced by the presence of plant residues. We, therefore, examined (1) how N immobilization varies with distance from the soil-residue interface and (2) whether abiotic immobilization occurs in agricultural soils. Spatiotemporal changes of N immobilization in the soil-residue interface were evaluated using a box that enabled soil to be sampled in 2 mm increments from a 4 mm-thick residue compartment (RC). The RC was filled with paddy soil containing ground plant residue (rice bran, rice straw or beech leaves) uniformly at a rate of 50 g dry matter kg⁻¹. Soil in the surrounding compartments contained no residue. After aerobic incubation for 5, 15 and 30 days at 25 °C, soils in each compartment were analyzed. After 5 days, significant depletion of inorganic N occurred throughout a volume of soil extending at least 10 mm from the RC in all residue treatments, suggesting extensive diffusion of inorganic N towards the RC. The depletion within 10 mm of the RC amounted to 5.0, 4.3 and 3.4 mg for rice bran, rice straw and beech leaf treatment, respectively. On the other hand, microbial N had increased significantly in the RC of the rice bran and rice straw treatments (11 mg and 5.5 mg, respectively) and insignificantly in the RC of the beech leaf treatment (0.06 mg). This increase amounted to 221% (rice bran), 129% (rice straw) and 1.7% (beech leaves) of the decrease in inorganic N within 10 mm of each RC. Thereafter the rate of N mineralization exceeded that of immobilization, and inorganic N levels had recovered almost to their original level by 15 days (rice bran) and 30 days (rice straw and beech leaves). These results suggested the predominance of biotic immobilization in soil near rice bran and rice straw and of abiotic immobilization in soil near beech leaves. No significant increase in both microbial and soluble organic N in the vicinity of beech leaves after incubation for 5 days further suggested that the abiotic process was responsible for the transformation of inorganic N into the insoluble organic N.     

Isolation of avian bornaviruses from psittacine birds using QT6 quail cells in Japan

Avian bornaviruses (ABVs) were recently discovered as the causative agents of proventricular dilatation disease (PDD). Although molecular epidemiological studies revealed that ABVs exist in Japan, no Japanese isolate has been reported thus far. In this study, we isolated four strains of Psittaciform 1 bornavirus from psittacine birds affected by PDD using QT6 quail cells. To our knowledge, this is the first report to isolate ABVs in Japan and to show that QT6 cells are available for ABV isolation. These isolates and QT6 cells would be powerful tools for elucidating the fundamental biology and pathogenicity of ABVs.     

Use of soil nonexchangeable potassium by paddy rice with clay structural changes under long-term fertilizer management

To prove the hypothesis that paddy rice utilizes soil nonexchangeable potassium (neK) and causes associated structural changes in clay minerals, K status and clay mineralogy of 22 surface soils from three paddy fields under long-term fertilizer management for 51–93 years were investigated. Soil neK content was determined as the difference between 1 mol L⁻¹ hot HNO₃ extractable K and 1 mol L⁻¹ ammonium acetate exchangeable K. Clay mineralogy was identified by X-ray diffraction (XRD). The radiocesium interception potential (RIP), an index of frayed edge sites in the interlayer sites of 2:1 type clay minerals, was also determined. The neK contents under the -K and NPK treatments were considerably lower than those under the unfertilized treatment in all the fields, indicating the exploitation of soil neK by rice. XRD analysis of the clay samples revealed 7% shift from the 1.0 peak to 1.4 nm one under the -K treatment compared with the unfertilized one, and the amounts of neK were negatively correlated with those of RIP (p < .01), suggesting the expansion of interlayer spaces of the 2:1 type phyllosilicates such as mica due to the release of neK. In addition, the neK content positively correlated with K balance of the long-term experiments (p < .05). The differences of neK between unfertilized K and -K treatments corresponded to 22–157 kg K ha⁻¹, or 0.42–1.68 kg K ha⁻¹ year⁻¹. In conclusion, utilization of considerable amount of soil neK under K depleted conditions should be considered to establish sustainable K management for paddy rice.