Feeding Habits And Selectivity Of Bellamya Purificata In Ecolofical Ditch

In recent years, the purification systems of ecological ditch are increasingly used for ex situ biorestoration of water quality in cultured fish ponds. Gastropods are an important constructional element of the water purification systems. From the perspective of food chain, we focused on the feeding habits and diet selectivity of Bellamy a purificata, which for examining its function in the ecological ditch.. In the present study, we analyzed the composition of ecological ditches, the composition of freshwater snails and the food organisms in ecological ditches, and also its density and biomass during the seasonal variation. A total of121gut content samples were obtained and the feeding habits and diet selectivity were analyzed. The mainly study results are as follows:1. There are five species of freshwater snails in the ecological ditch, which are Bellamya purificata, Alocinma longicornis, Parafossarulus eximius, Parafossarulu sstriatulus and Radix ovata. They all belong to3families4genera, including2families3genera4species in Prosobranchin and1families1genera1species in Pulmonata. The density and biomass of freshwater snails was highest in autumn, lowest in winter. Takeing the comprehensive frequency, density, biomass and dominance into consideration, Bellamya plays the most important role in ecological ditches. It is the dominant species for the highest idensity and biomass in autumn and lowest in winter.2.The investigation of the Bellamya purificata’s food organisms in ecological ditch:①Phytoplankton:in total of8phylum74genera, including12genera in Cyanophyta,38genera in Chlorophyta,11genera in Bacillariophyta,5genera in Euglenophyta,2genera in Crypophyta,2genera in Pyrrophyta,1genera in Xanthophytaand3genera in Chrysophyta.②Periphytic algae:in total of7phylum54genera, including5genera in Cyanophyta,26genera in Chlorophyta,15genera in Bacillariophyta,3genera in Euglenophyta,2genera in Crypophyta,2genera in Pyrrophyta and1genera in Xanthophyta.③Zooplankton:18genera in protozoa,16genera in rotifera,4genera in Cladocera,1genera in Copepoda and nauplius. Because the floating beds and submerged plants inhibit the growing of the algal and benthic biota feed on algae, the density and biomass of algae and zooplankton in the spring and winter is much larger than in summer and autumn.3. The feeding habits of Bellamya purificata:①Feeding intensity:Bellamya purificata feeding in spring, summer and autumn, but no feeding in winter. Empty gut rate in spring is larger than in summer and autumn.②Diet composition:the food item can be approximately divided into four groups, such as algae, small invertebrates, debris, and others (including macrophytes and unidentified items). Algae and debris are the main food source of Bellamya purificata.③Seasonal changes of diet conposition:schoener overlap index shows that there is no significant differences among the four seasons.④Feed selectivity:Bellamya purificata has preferences on Cyanophyta, Chlorophta, Bacillariophyta, Euglenophyta and Xanthophyta, while it shows negative selective on Pyrrophyta, Cryptohyta, Protozoa and Rotifer.According to the diet composition, Bellamya purificata acts as a component of ecological ditch water purification system. It can remove algae and debris, which may increase the organic loading and even cause blooms. If Bellamya purificata reasonable stocked and utilized with other biological components like bacteria, higher aquatic plants, other large benthic fauna, as well as fish in ecological ditch water purification system, it can purify water well.