Comparative efficacy of candling and glass plate compression for detection of diphyllobothriosis in rainbow trout (Oncorhynchus mykiss) musculature.

The efficiency of the direct candling technique on fillets (candling 1) was compared with examination of cuts 4 mm thick or less (candling 2) and glass plate compression for the detection of plerocercoids of Diphyllobothrium spp. in muscles of rainbow trout, Oncorhynchus mykiss. Application of the three procedures gave the following results (percentage of infected fish/percentage of isolated plerocercoids): candling 1: 40.9/22, candling 2: 29.5/18.8, glass plate compression: 29.5/59.2, and combination of candling 1 and 2: 70.5/40.8. The combination of the three techniques yielded 100% sensitivity: 44 infected fish were detected of 77 trout examined. When different regions of the musculature were compared using the three techniques, a high density of plerocercoids and the highest percentage of infection (90.9%; 40 infected trout) were detected in the ventral musculature. Candling 1, candling 2 and glass plate compression on the ventral musculature gave the following case numbers and percentages, respectively, for the total of 44 cases: 9 (20.5%), 9 (20.5%), and 22 (50%).