Morphological comparison of in ovo derived and naturally occurring flukes using Microphallus similis, M. pygmaeus and Maritrema arenaria

This investigation deals with the evaluation of the in ovo technique for the cultivation of trematodes. The technique has previously been used for the maturation of digenetic flukes and the establishment of life cycles in the laboratory but it was not known if the adult flukes produced were morphologically comparable to those found in their natural hosts. Three species of microphallids, Microphallus similis, M. pygmaeus and Maritrema arenaria were used. Metacercariae of each species were inoculated into fertile hen's eggs which were incubated at 41°C for 120 hours. The adult flukes recovered were stained and mounted and morphonietric measurements obtained were compared to definitive descriptions of the three microphallid species. The results showed that the in ovo technique provided adult flukes which were indistinguishable from those occurring in natural hosts.

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.

In ovo cultivation of Microphallus primas (Trematoda: Microphallidae) metacercariae to ovigerous adults and the establishment of the life-cycle in the laboratory

This investigation reports for the first time the establishment of a trematode life-cycle in the laboratory using in ovo cultivation of the adult stage. Microphallus primas metacercarial cysts were removed from Carcinus maenas crabs and chemically excysted. Using a modification of the technique developed by Fried (1962) the released metacercariae were grown in fertile hen's eggs to ovigerous adult flukes. These were removed from the under surface of the chorio-allantoic membrane of chick embryos 5 days post-infection and the fluke eggs recovered were used to infect laboratory-reared Hydrobia ulvae snails. When challenged against parasite-free crabs the cercariae released from the experimentally infected snails gave rise to metacercarial cysts that were again identified as M. primas.