Diplostomum spathaceum

The eye fluke Diplostomum spathaceum is one of the most common and abundant parasites of fish in freshwater and fish-farm systems across the Palearctic. Its life cycle involves lymnaeid snails as first intermediate hosts, a variety of fish species (>125) as second intermediate hosts, and piscivorous birds (especially gulls and terns) as definitive hosts. Vast numbers of cercariae are released from an infected snail into the water. In fish, infection takes place via direct penetration of free-swimming cercariae through the skin or gills. D. spathaceum causes the disease diplostomiasis, which may have important implications for fish farming. Metacercariae live in the crystalline lens of fish, causing cataracts. Heavy infection can result in acute mortality, while cataracts characterize chronic infections. Infection can cause deficient feeding, retarded growth, and reduced survival. Currently, a key tool to control diplostomiasis in aquaculture is to eradicate the snail intermediate host.