Observation on Collecting Oncomelania hupensis When Opening The Sluices During Flood Season in Yangtze River

Abstract

To ascertain whether Oncomelania hupensis can spread into the ditch when a floodgate was open, an observation was made in the snail-ridden area during the flood season of Yangtze River in Jia Yu County from July to September 1987. The snails were collected at the ditch inside the floodgate for 71 hours and 25 minutes within 9 days. The flow through the net was 179-982 m³, 145 snails were gained with blocking net at the flow speed of 0.02-1 meter/second, its average density was 0.81 snails/1000 m³ (0.21-6.73 snails/1000m³). The number of gained snail at the lower section of the ditch were 6.25 times as high as that caught at the upper section. The number of snails in water was decreasing with the depth of the water. The area of 846 m² was scooped inside the floodgate for 5 days, its average density was 1.52 snails/m². The area of 220 m² was scooped around the opening outside the floodgate for 4 days, its average density was 0.63 snails/m² of all the gained snails, 98.79% were young with a whorl under 6.5 The result showed that when the floodgate was sluiced for irrigation, snails could spread into the ditch and thus snail-ridden areas increased accordingly.