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Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam. [ABSTRACT FROM AUTHOR]

The black carp,Mylopharyngodon piceus, is used for biological control of freshwater mollusks in various parts of the World. Fish-borne zoonotic trematodes (FZTs) are a public health concern in Vietnam and we suggest using black carp in nursery ponds, which are important for FZT transmission, to control snails serving as first intermediate hosts. However, the use of large juvenile (>2 kg) black carp in nursery ponds could be problematic and we decided to determine consumption rates by black carp of various sizes and their choice of different sizes of selected snail species found in aquaculture ponds in northern Vietnam. Furthermore, shell strength of common snails was assessed. Average daily consumption as percentage of fish weight ranged from 8.12% for smaller fish (100–250 g) to 4.68% in the larger fish (610–1250 g).Bithynia fuchsiana, the intermediate host ofClonorchis sinensis, and some intestinal trematodes were readily consumed by even the smallest black carp tested. The proportion ofMelanoides tuberculata, an important host for intestinal trematodes, declined with an increase in its shell height. The same was observed for two viviparid snail species,Angulyagra polyzonataandSinotaia aeruginosa; these species do not serve as first intermediate host for FZTs. Small black carp (100–250 g) consumed 50.4% of the second largest size class (26–30 mm) and 19% of the largest size class (>30 mm), while medium-sized black carp consumed 49.6% of the largestM. tuberculataand almost all snails of other size classes. Large black carp consumed 75% of the largest size class (>30 mm) ofM. tuberculata. Crush resistance (loge-transformed) increased linearly with shell size (loge-transformed) in most species tested. Crush resistance was the lowest inB. fuchsiana, while there was an overlap betweenM. tuberculataand the viviparid snails. We concluded that black carp of smaller size preferentially fed onM. tuberculata. [ABSTRACT FROM PUBLISHER]