Infestation of littorinids by larval Digenea around a small fishing port

Larval Digenea infectingLittorina rudis, L. littoreaandL. obtusataaround Portavogie harbour, Co. Down, were examined. High levels of infection were found among the littorinids collected from sites on the harbour shore, though levels of infection varied somewhat with position on the shore. There was a direct relationship between size of the snail host and likelihood of infection. There was a negative association between certain pairs of helminth species in the same host, particularly where the rediae ofCryptocotyle linguaorHimasthlasp. were involved. Infection rates in gastropods declined away from the harbour and it is concluded that the high infection rate centres around the harbour were probably due to the increased concentration of definitive hosts, mainly seagulls, attracted to this area by dumping of raw fish offal. The infection ofPholis gunnelluswith the metacercariae ofC. linguawas also examined. Older fish were more heavily infected than younger fish but no direct relationship was found between high snail infection rates and highP. gunnellusinfection rates.