Population, Morphology and Ultrastructures Gonads Adaptation Changed Between Unsuitable and Original Breeding Habitats in Oncomelania hupensis

Abstract Background: Weishan Lake and its surrounding areas represent an important water conduit and storage reservoirs for the Eastern Route due to the South to North Water Diversion Project. It was listed as a potential endemic area for schistosomiasis by the Ministry of Health Schistosomiasis Advisory Committee. Oncomelania hupensis is the unique intermediate host of Schistosoma japonicum in China. To determine whether Oncomelania hupensis could establish colonies in Weishan Lake once introduced from original habitat, in May 2004, 2000 adult Oncomelania hupensis were transplanted from the original habitat to isolated snail cages in Weishan Lake. Results: From October 2005 to October 2016, Oncomelania hupensis were bred in isolated snail cages in Weishan Lake, and samples of the original habitats were collected. The population was monitored, and the morphology of Oncomelania hupensis was measured. Gonads were sectioned and observed under transmission electron microscopy. Oncomelania hupensis could still continually reproduce its population 12 years after transplantation to Weishan Lake. Comparing the morphology with that of animals from the original habitat, it was found that the snail shell length, shell width and aperture width decreased in 2005, and significant changes were observed in the ultrastructure of sperms (axoneme and the 9+2 the axoneme coarse fibers were absent, and chromatin density decreased in the head of the sperm cells) and oocytes (nucleus swelling, endoplasmic reticulum, pale vesicles and lipidosomes decreased and chromatin was absent) of snails breeding in Weishan Lake.Conclusions: Although abnormal development of the ultrastructure of Oncomelania hupensis reproductive gonad was observed, they still survived for 12 years, which might reflect a survival strategy in which the snail trades a degree of fecundity to survive though harsh winters.