Survival of heterophyid metacercaria in common carp (Cyprinus carpio).

Heterophyidae are small intestinal trematodes that infect vertebrates worldwide. Common carp (Cyprinus carpio) is one of the most preferred freshwater fish species by consumers in Asia, the region where fish-borne trematodes like Heterophyidae are most prevalent. How long Heterophyidae survive in common carp is unknown. The objective of this study was to quantify survival of Heterophyidae in common carp after experimental exposure. Fish of 0.18 g were either used as controls or exposed to 250 heterophyid cercaria for 24 h. Control fish did not become infected. Percentage infection of exposed fish at 0-2 (n = 53), >2-10 (n = 15), >10-20 (n = 11), and >20-27 (n = 33) weeks post exposure was 98, 80, 100, and 100 % respectively. The number of metacercaria per fish did not significantly decrease (P = 0.19) during 27 weeks after exposure: exp [3.6200-0.0193 × weeks post exposure]. All developed metacercaria were identified as Haplorchis spp. It was concluded that Heterophyidae may persist in carp for a long time, implying that harvestable carp are a risk to human health.