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KMID : 0380319750150000239
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Journal of Korean Research Institute for Better Living
1975 Volume.15 No. 0 p.239 ~ p.262
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The Relation of Freshwater Environment and Hydrochemical Properties to the Presence of the Snail, Parafossarulus manchourius Bourguigant, in Korea
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Abstract
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The present investigation was carried out in the last year to clarify the relation of freshwater environments and hydrochemical properties to the occurrence of the snail, Parafossarulus manchouricus, the Ist intermediate host of Clonorchis sinensis which is the causative parasite of clonorchiasis recognized as an important endemic in Korea.
Twenty three riverside areas among 30 places selected were 7 in the HanRiver, 8 in the NagdongRiver and 8 in the MankyeongRiver. Three of the heavily polluted areas(wastewater) were located along the Joongnang stream and Moraenae, and others were reservoirs located in Kyeonggido.
Samples of water were taken in May, July and October, repeatedly from the same areas for the chemical analysis. The results are summarized as follows;
1. Remarkable increase in the numbers and infection rates of intermediate hosts were observed in July. Snails(1.6%) in the NagdongRiver and freshwater fishes(36.0%) in the MankyeongRiver showed the highest infection rates, respectively. No snail and freshwater fish were found in the heavily polluted streams.
2. Range of flowing velocities obtained in the habitat areas was 0-6.5㎝/sec and in the contrast areas was 11.5-32.0㎝/sec. The flowing velocity was considered to be an important physical factor influencing the distribution of the snails.
3. The range of specific gravity of the water over all areas was 0.990-1.006 and no remarkable difference between the habitat water and the contrast was noted. The snails live among the floating shore vegetation mostly in turbid water of the rivers or reservoirs.
4. Contents of each chemical component, such as pH, total acidity, total alkalinity, total hardness, NH_3-N, NO_2-N, NO_3-N, RE, Cl^- and SO_4^--show remarkable seasonal variation with the peak in July, particularly in case of wastewater. In the comparison of the results of "t" test, no significant differences were found between both of the waters with or without occurrence of the snails.
5. The range of BOD of the nonoccurrence water was relatively higher than that (30.26-36.43ppm) of the inhabited water, and DO of the nonoccurrence was significantly lower than that(≤3.8ppm) of the inhabited water.
From the above results an inference can be drawn that adequate ranges of flowing velocity, DO, and BOD are responsible for the occurrence, survival and multiplication, and possible spread of the snail in the different bodies of water in the rest of the great area in Korea.
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