Infection with trematodes Apophallus sp. affects the growth and activity of hydrolytic enzymes in the invasive gravel snail Lithoglyphus naticoides.

Currently, the alien freshwater gastropod Lithoglyphus naticoides is rapidly expanding its range and promoting the spread of parasitic trematodes Apophallus sp. These flatworms use the snail as intermediate host and may cause the dangerous black-spotted disease in fish juveniles. However, despite the obvious importance of knowing the physiological bases of this host-parasite interplay, studies in this area remain scanty. Therefore we focused on the size-weight and physiological parameters of L.naticoides and their changes in response to Apophallus infection. It was found that the shell height and total body weight significantly increase in the infected molluscs. In contrast, protease activities were significantly lower in infected than in naïve snails over a wide pH range. Inhibitor analysis showed the presence of serine-, cysteine- and metalloproteinase activity in L.naticoides. Trematode infection most strongly affected the serine proteinases, reducing their activity levels. At the same time, the infection did not cause a decrease in α-amylase activity in the gravel snails. Moreover, at certain pH values, α-amylase activity was significantly higher in parasitized than in non-parasitized specimens. These metabolic features may contribute to growth acceleration in parasitized hosts, thereby affecting their survival and spread, which eventually may have far-reaching consequences for the reservoir ecosystems.