Diversity and distribution of freshwater molluscan fauna in reservoirs and headwater streams of the Kala Oya river basin in Sri Lanka

In this study, the variation of aquatic molluscan diversity concerning seasonal water level fluctuations (WLF) and sediment texture was investigated in some perennial irrigation reservoirs associated head headwater streams Kala Oya river basin Sri Lanka. Altogether 11,752 specimens belonging to 10 gastropod taxa (96.6%) 2 bivalve (3.4%) were identified. Of these, 11,282 (96.0%) from reservoir sampling sites remainder 470 (4.0%) streams. gastropods, individuals genus Melanoides showed highest distribution index (DI) 0.75 followed by Bellamya (DI = 0.63) Thiara 0.60). The DI molluscs a significant positive relationship with their shell size (p < 0.05). Although richness comparatively lower than sites, Viviparidae (Bellamya; 0.06±0.03), Bithyniidae (Bithynia; 0.21±0.07) Thiaridae (Thiara; 4.8±1.9 Melanoides; 1.1±0.8) higher relative abundance (expressed as per dm3) fluctuation negative 0.05), but not Shannon-Weaver 0.073). also found be related where most abundant genera Bellamia, Bithynia, widely distributed sandy substrates basin.