Malacological Studies on Parafossarulus manchouricus(Gastropoda: Prosobranchia) in Korea (한국산(韓國産) 왜우렁(Parafossarulus manchouricus)의 패류학적(貝類學的) 연구(硏究))
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- The Korean Journal of Malacology
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- v.1 no.1
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- pp.24-50
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- 1985
Five different populations of Parafossarulus manchouricus (Chongpyung, Chinju and Kunsan, Korea; and Japan and Taiwan), a population of Bitbynia (Gabbia) misella (Gongju, Korea) and two different populations of Bithynta tentaculata (Michigan, U.S.A. and Bodensee, Germany) were compared in regard to eff-laying characteristics, morphology, chromosome cytology, natural infections of parasites and ecology of habitats. A satisfactory culture method was devised for laboratory rearing of the snails. Tropical fish food (Terra SML) and powdered green leaves (Ceralife) were used as the main food sources for the snails. Benthic diatoms such as Navicula and Gomphonema from the periphyton were also essential for satisfactory growth, especially for the baby snails. The aquaria were stabilized with small stones from a local stream. Young P. manchouricus snails grew to adult size in about 54 days after hatching. They laid eggs 150-156 days after hatching. The whole cycle (birth to egg-laying) took approximately 5 months. The three species of bithyniid snails are iteroparous and lay eggs once a year. There were no major morphological differences in the shells of genera or subgenera studied here. They did exhibit the following rather minor differences. The shell of Parafossarulus has spirally raised ridges, and its apex is usually eroded; the other two genera lack these characteristics. The shell of B. (Gabbia) misella is small, nor exceeding 7.5 mm in length, while the shells of the other two species are larger, being more than 10 mm in length. Scanning electron microscopy (SEM) of the protoconch of P. manchouricus reveals nearly smooth sculpture with small, low, spiral wrinkles. This sculpture is quite different from that of the Hydrobiidae, a family to which the bithyniids are frequently assigned. Scanning electron microscopy of the radulae of the three bithyniid species showed that their radular morphologies are very similar, but there are some small differences, which may be species-specific. There were some statistical differences in shell heights between the Korean and the other populations of P. manchouricus, and between this species and the other two bithyniids as well. The shell differences between the several populations of Korean P. manchouricus may be related to environment. Edtails of the chromosome cycle of these bithyniid snails are similar to those reported for other snails. No specific differences were observed in the chromosome cycle between the various species and populations of snails employed in this study. Reporred for the first time in molluscs are two darkly stained "nucleolar organizers" during pachyterne stages of meiosis. Two different chromosome numbers were observed in the three bithyniid species: n=17 in B. tentaculata and P. manchouricus, and n=18 in B. (G.) misella. no sex chromosomes or supernumerary chromosomes were seen. There were no morphological differences in karyotypes of three Korean strains of P. manchouricus. The infection rates of cercariae of Clonorchis sinensis in Chinju and Kunsan strains of P. manchouricus were 0.14% and 1.25%, respectively. However, Clonorchis cercariae were found in Chongpyung strain of P. manchouriceu and Gongju strain of B. (G.) misella. The habitats of P. manchouricus around Jinyang Lake were relatively clean without any heavy pollution of aquatic microorganisms and organic materials during the period of this study. The levels of dissolved oxygen (D.O.) and biochemical oxygen demand (B.O.D.) of the water specimens sampled from the study areas ranged from 6.0 to 9.6 ppm and from 0.4 to 1.6 ppm, respectively. Eight metalic constituents from the water samples were also assayed, and all metalic ions detercted were remarkably low below the legal criteria. However, calcium ion in the water samples from the habitats of P. manchouricus was considerably higher than others.
For the stable and high yields of low-land rice in Korea, the characteristics of rice plant for the vegetative and physiological responses, plant type formation, and yield components have been studied in order to obtain the fundamental data for the improvement of cultural practices, especially for the ideal fertilizer application. Furthermore the environmental conditions in Korea including temperatures, light, precipitation, and soil conditions have been compared in the broad sense with those in Japan, and the application of nitrogen, phosphorus, potassium, silicate and other micro-nutrients were described in relation to the characteristics of environmental conditions for the improvement of fertilizer application. 1. The average yield of polished-rice per 10 are in Korea is about 204 kg and this values are much less than those in Japan and Taiwan where they produce 77% to 13% more than in Korea. The rate of yield increase a year in Korea is 4.2 kg, but in Japan and Taiwan the rates of yield increase a year are 81 % and 62%, respectively. It was also found that the coefficient of variation of yield is 7.7% in Korea, 6.7% in Japan and 2.5% in Taiwan. This means that the stability of producing rice in Korea is very low when compared with those in Japan and Taiwan. 2. It was learned from the results obtained from the 'annual yield estimation experiment' that there are big differences in the respect of plant type formations between rice crops grown in Japan and Korea. The important differences found were as follows: (1) The numbers of spikelets per 3.3 square meters are 891 in Korea and 1, 007 in Japan(13% more than in Korea). (2) The numbers of tillers per 3.3 square meters at the stage of maximum tillering are 1, 150 in Korea, but in Japan they showed 19% more than in Korea. (3) The ratio of effective tillers to total tillers is 77.5% in Korea and 74.7% in Japan, which seems to be higher in Korea than in Japan. But the ratio in Korea is very low when considered the numbers of total tillers in both countries. (4) The ratio of grain to straw is 85.4% in Korea and 96.3% in Japan. 3. The average temperatures during the growing season at the area of Suwon, Kwangjoo and Taegu are almost same as those in the district of Jookokoo(Fookoo yama) in Japan, i.e., the temperatures during the rice-growing season in Korea are similar to those in the southern-warm regions of Japan. 4. Considering the minimum temperatures at the stage of limiting transplanting, 13