Life-cycle description and comparison of Diplostomum spathaceum (Rudolphi, 1819) and D. pseudobaeri (Razmaskin & Andrejak, 1978) from rainbow trout (Oncorhynchus mykiss Walbaum) maintained in identical hosts.

Precise identification of members of the genus Diplostomum is difficult in that many larval stages have been described and named separately from their adult forms. In this study, the life cycles of two Diplostomum spp. were established using metacercariae obtained from the eyes of rainbow trout. The parasites were identified as D. spathaceum and D. pseudobaeri using a procedure and key devised by Shigin. Each life cycle was completed in the laboratory using domestic chickens (Gallus gallus domesticus L.) as definitive hosts and Lymnaea peregra (Muller) and rainbow trout as first and second intermediate hosts, respectively. Utilizing identical hosts minimised host-induced morphological variations and allowed comparisons of anatomical features to be made. Light and scanning electron microscopy were used to study each developmental stage and detailed descriptions of the life cycles were compiled. The results obtained may go some way to resolving the confusion that surrounds Diplostomum taxonomy.