The immune response in immunized and naturally infected rainbow trout (Salmo gairdneri) to Diplostomum spathaceum as detected by enzyme-linked immunosorbent assay (ELISA).

The enzyme-linked immunosorbent assay (ELISA) procedure was modified and adapted for detection of circulating antibodies in rainbow trout (Salmo gairdneri) against metacercariae of the digenean trematode Diplostomum spathaceum, the causative agent for diplostomiasis. Rainbow trout (Salmo gairdneri) were injected with sonicated metacercariae representing 10, 40, and 100 metacercariae per fish. Three weeks after immunization the average titers for trout injected with 10, 40, and 100 metacercariae were 874, 841, and 525, and by six weeks the titers had fallen to 299, 349, and 203, respectively. Nine weeks after initial immunization, two remaining fish initially immunized with 100 metacercariae per fish were injected with a booster of 50 sonicated metacercariae per fish. Four weeks later the average titer was 1204. Serum samples from naturally infected wild fish tested for the presence of circulating antibodies against Diplostomum spathaceum showed 25 of 27 with positive titers.