POPULATION-DYNAMICS OF MELANOIDES-TUBERCULATA (THIARIDAE) SNAILS IN ADESERT SPRING, UNITED-ARAB-EMIRATES AND INFECTION WITH LARVAL TREMATODES

A dense population of Melanoides tuberculata was found at a brackish ( 5.93-6.98%) desert spring in the United Arab Emirates. A total of 232- 300 snails were measured and examined for larval trematodes during the period January 1990 to January 1991. The relative abundance of variou s size classes of the snail has shown that the mass release of young s nails occurred twice a year, in April-May and September-October. Seven different forms of cercariae were found: A xiphidiocercaria, a brevif urcate cercaria, two pleurolophocercous cercariae, two gymnocephalous cercariae, and the cercaria of Philophthalmus gralli. The overall infe ction rate of this snail was 73.6% and ranged from 51.3 during Februar y-March 1990 to 91.7% during January 1991. The xiphidiocercaria and th e P. gralli cercaria were the most abundant and were found in 21.1% an d 29.7%, respectively, of the examined snails. A relatively high rate (9.5%) of double infection was found. Cases of triple infection were a lso encountered.