Limnological Pre-survey of Lake Phewa, Nepal

Article信州大学理学部紀要 15(1): 27-29(1980)departmental bulletin pape

Life cycle of Peridinium bipes f. occulatum (Dinophyceae) isolated from Lake Kizaki.

Encystment and excystment in the life cycle of a dinoflagellate Peridinium bipes f. occulatum (Lindem.) Lef., which was isolated from Lake Kizaki, were investigated by use of a clonal population. Sexual reproduction was induced in P. bipes inoculating exponentially growing cells into N-free Carefoot's medium. The sexual life history of P. bipes resembles that reported for P. willei and P. cinctum in many respects: isogampus and homothallic gamete; the gametes resemble small, naked, vegetative cells ; lateral fusion with a long living planozygotic stage in which the zygotes enlarge and become warty ; hypnozygote with 3 walls (exsospore, mesospore and endospore); hypnozygote characterized by one or more large red oil droplets. However, the difference of P. bipes from P. cinctum and P. willei is that the post-zygotic cell of P. bipes divided into one cell with a red oil droplet and one without it. From the encystment experiment of P. bipes, very low encystment was observed below 10℃. The temperature range which permitted encystment was 15 to 25℃. Although cyst formation was observed even in continuous dark, the frequency of encystment increased with the light intensity. Under continuous dark conditions, no excystment was observed at any temperature from 5 to 25℃. The cysts illuminated at 105 μE/㎡/S excysted at the frequency of 81 % after 13 days incubation at 15℃, and lower light intensities led to decreases in germination frequency. Excystment frequency of this species depended on light intensity. The experiments described here demonstrate that light is a critical factor in the germination of P. bipes cysts, affecting excystment frequency.Article信州大学理学部紀要 27(2): 87-104(1993)departmental bulletin pape

Diel vertical migration of Daphnia in Lake Kizaki : Difference in its pattern depending on the daphnid's body size

The pattern of diel vertical migration (DVM) of Daphnia galeata was analyzed in summer in Lake Kizaki (a small mesotrophic lake) with maximum depth of 29.5 m. Juveniles, small adults and medium-sized adults stayed the whole day at 4-8, 8 and 14 m depths, respectively, and did not perform DVM, while large adults showed DVM between 14 m and near the bottom layer (26-27.5 m). Smaller adults had larger clutch sizes relative to their body size and allocated more energy to reproduction than larger adults. They might have compensated for loss due to predation by producing abundant offspring in the epilimnion where the food level was higher. On the other hand, the larger adults performed DVM to reduce mortality due to predation at the cost of reduced reproductivity induced by environmental factors in the hypolimnion (low concentrations of food and oxygen). The study thus demonstrated that even a single population of Daphnia can show different DVM patterns depending on body size (life stage).Article信州大学理学部紀要 32(2): 77-88(1998)departmental bulletin pape

CT and MRI findings of thymic carcinoid

Objective: To evaluate the CT and MRI findings of thymic carcinoid and to compare these findings with previously published findings of thymoma. Methods: 11 cases of pathologically proven thymic carcinoid were reviewed retrospectively. Three patients had typical carcinoid, and eight patients had atypical carcinoid. The characteristics of the tumours and related thoracic abnormalities were assessed in each case on CT and/or MRI by two chest radiologists. The final decisions on the findings were reached by consensus. Results: Thymic carcinoids were more likely to have a large mass (ranging from 18 to 105 mm), irregular contours (n=8), heterogeneous intensity on T2 weighted images (n=6; eight patients underwent MRI), heterogeneous enhancement (n=9) and local invasion (n=7). A necrotic or cystic component was identified in seven patients (one typical carcinoid and six atypical carcinoids). Lymphadenopathy was seen in four patients. Septum, capsule, haemorrhage and calcification were seen in three patients, two patients, two patients and one patient, respectively, with atypical carcinoid. Conclusion: Thymic carcinoids tend to have a high prevalence of large masses, irregular contours, heterogeneous intensity on T2 weighted images, heterogeneous enhancement and local invasion on CT and/or MRI. A necrotic or cystic component is often seen in atypical carcinoid. Advances in knowledge: Radiologic features of thymic carcinoid mimic those of high-risk thymomas and/or thymic carcinomas