The Relationship Between Parafossarulus Manchouricus, the Snail
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[Jpn. J. Parasitol., Vol. 44, No. 2,95-105, April, 1995] The Relationship between Parafossarulus manchouricus, the Snail Host of Clonorchis sinensis, and Water Qualities During the Growth Season in Okayama Prefecture, Japan FUMIO OHYAMA, Tetsuya OKINO, Motota SHIMIZU AND Ryo HATSUSHIKA (Accepted for publication; February 28, 1995) Abstract The relationship between the distribution, abundance, productivity, growth of Parafossarulus manchouricus, the snail host of Clonorchis sinensis and water qualities; water tempeature (WT), hydrogen ion concentration (pH), dissolved oxygen (DO), calcium (Ca) and chlorinity (Chi), were surveyed at 20 stations of 6 areas in Okayama Prefecture, Japan during the growth season from July to September in 1991. Two types of analysis were applied to the water quality parameters retroactively treated from the time of snail examination in September. One was comparative analysis of the water quality parameters at snail positive (+) and negative (-) places; Ca and Chi at snail (+) areas were significantly higher than those at (-) areas and no difference was found in WT, pH and DO, but within snail (+) areas differences of Ca and Chi between snail (+) and (-) stations were not significant. The other was correlation analysis between water quality parameters and snail param eters; abundance, productivity and growth at snail (+) stations: WT correlated with productivity (^=0.63-0.82) and weakly correlated with abundance and growth; pH weakly correlated with abundance, productivity and growth; DO weakly correlated with abundance and productivity; Chi correlated with abundance (r5=0.77-l .00) and productivity (rs=0.11-0.96). The correlations between WT, pH and DO in water samples suggest that the snail (+) stations were strongly affected by photosynthetic organisms. The effect of WT to the snail might be not only direct one but also indirect one through the richness of foods. The effect of Chi might also be indirect through the foods. The correlations between snail and pH, DO might be the reflection of the photosynthetic activity by the aquatic organisms which would supply foods for the snail. No correlation with Ca might be showed by the masking by other strongly correlated factors or by the too narrow range of Ca measurements to show the correlation. Key words: Parafossarulus manchouricus, snail host, Clonorchis sinensis, water quality, growth season Introduction Soh etal. (1980) and Miyasaka (1983), but not have been discussed well. One possible reason for this is Parafossarulus manchouricus, the snail host of that there were few studies on the breeding season Chinese liver fluke, still widely distributes in strongly affecting the existence of snail. Another southern Okayama in Japan (Nagahana et al., 1978) reason may be that the most of studies were based on and the life cycle of Clonorchis sinensis in Okayama presence/absence study which was not necessarily completes through the reservoir hosts though the to uncover the relationship between water quality human route is very rare (Nagahana et al, 1980, and the snail as mentiond by Dussart (1979). 1984; Hatsushikae/a/., 1986). In the present study, the snail and the water On water quality at the habitat of this snail there quality were examined during the growth season have been many reports by Inatomi (1953), Sugihara which will strongly affect the population and growth et al (1961), Sugihara (1964a, b, c), Min (1975), of this species. To compensate a weak point of the presence/absence study, a correlation analysis be Department of Parasitology, Kawasaki Medical School, tween snail parameters and water quality param Kurashiki 701-01, Japan. eters within snail (+) stations was also done. Furthermore we adopt the analysis by the retro- 96 active treatment for the data of water quality, which done from 15 July to 21 September 1991 with an made the analysis of water qualities possible from exception of rainy days (Figs. 1,2). Each series of the time of last snail measurement to 2 months the sampling was performed within 5 hrs around before. We were thus able to obtain more reliable 1:00 PM to avoid diurnal fluctuation except the results than that from the only one series of water cases with snail collections. And in order not to be measurement at the snail habitats by the ordinary sampled at the fixed time in a day, the sampling method used by previous workers (Sugihara, 1964a, order among 6 areas was randomized in each series b, c; Sugihara et al.9 1961; Min, 1975; Miyasaka, as much as possible with trading-off the shortening 1983). In addition we considered the total weight of of the total moving time among areas. All the water all snails at each station, which can be regarded to samples were taken at 10 cm below the water sur the index of biomass for snail. This parameter face. When the water was not deep enough, superfi would be a reliable and convenient to know the cial water was sampled. The temperature, dissolved 'productivity' of the snail population. oxygen and pH of water body were measured at each We hereby revealed the relationship between P. station with a set of portable electronic instruments manchouricus and basic water qualities; water tem (Aqua Checker U-7, HORIBA Ltd., Japan). The perature, pH, dissolved oxygen, calcium and chlo- chlorinity was estimated by a silver nitrate method rinity. and the calcium concentration was by an EDTA method. Materials and Methods The snail examinations were done twice at the beginning of the study to get the information of the A total of 20 stations of 6 areas were selected for abundance of yearling snail, and at the end to get the this study in the southern part of Okayama Prefec information of the abundance, productivity and ture, where nine series of water samplings were growth of newborn snails. Okayama 134' E Fig. 1 Map of the study site (A-F). A: Tamashima (5), B: Mizushima (2), C: Urayasuni- shimachi (4), D: Urayasuhonmachi (3), E: Kogushi (1), F: Suimoncho (5). The numerals in the parenthesis indicate the numbers of examined stations. 97 Jul. Aug. Sep. 15-22 17 24 8 14 20 4 17-21 Ca.Chl A A A A A Water WT. pH, DO A A A A A A A A Snail 0 month 0. 5 months 1 month 1.5 months 2 months Fig. 2 Time table of water sampling and snail collection, and the retroactive periods from the last collection of the snail. Open triangle shows a series of water sampling for Ca, Chi, WT, pH and DO; Dark triangle shows a series of snail collection. A hand-collection method for 30 person-minutes Results and Analyses was applied at each station. In the rice fields, the snails were searched on the mud surface and algae The obtained results of water temperature, pH, around stems of rice plants and weeds. In the canals, dissolved oxygen, calcium, chlorinity are summa they were searched on the mud surface at the bottom, rized in Table 1. There were 7 snail (+) stations and at canal walls and on scooped algae or plants. The 13 (-) ones. The measurements of water qualities collected snails were classified to two groups of were showed in Fig. 1. At snail (+) 7 stations the yearling and newborn, and counted separately. Then range of water temperature was 23.4-39.3°C, pH at the second series of snail examination the shell was 6.9-9.2 and dissolved oxygen was 3.1-17.5mg/ length was measured, and the total weight was 1. Calcium concentrations were gathered in a narrow weighed together with all individuals collected from range of middle class of the hardness (14.1^4-7.3mg/ each station after cleaning off the mud and small 1). The range of chlorinity was wide (11.3-306.9 organisms from the shell surfaces. The snails cap mg/1). tured at the first series of collections in July were The relationship within water quality parameters released back into the same stations within a day not themselves was analyzed by Pearson's correlation to disturb the natural population. coefficient for all water samples from snail (+) Besides collections of P.manchouricus not only stations (Table 2). Water temperature, pH and dis other snails but also vegetations were visually ob solved oxygen showed definite positive correlation served and took photos every time of water sam each other (P<0.002). pling. A comparative analysis of the water quality pa The representative values of water quality pa rameters at snail (+) and (-) areas, and snail (+) and rameters were taken by retroactive averaging from (-) stations within snail (+) areas were presented in the time of the second series of snail collection to the Table 3. There were no significant differences in time to be treated (Fig. 2). The snail parameters of water temperature, pH and dissolved oxygen in the abundance, growth, and productivity were indexed two combinations. The calcium levels and chlorin by the values of the number, mean length, and total ity at 14 stations of snail (+) areas were significantly weight of the snails at each snail (+) station in the higher than those at 6 stations of the snail (-) areas second series of snail collection in September. (p<0.01), but these differences were not significant in the combination 2 between the snail (+) and (—) stations within the snail (+) areas. 98 Table 1 Measurements of water qualities at 20 stations of P. mancouricus habitats from July to September 1991 in Okayama Prefecture WT-°C pH DO-mg/1 Ca-ppm Chl-mg/1 Stations Snail Range Range Range Range Range Remarks (Mean) (Mean) (Mean) (Mean) (Mean) A-l 24.3-35.3 7.1-8.1 5.9-12.7 22.6-48.7 12.9-71.7 RF (30.2) (7.7) (10.0) (34.3) (52.3) A-2 + 25.2-36.5 7.1-9.2 5.7-17.4 24.7-36.3 12.5-187.3 RF (31.9)