STUDIES ON THE STRUCTURE, LIFE HISTORY AND ECOLOGY OF THE TREMATODE PHYLLODISTOMUM SIMILE NYBELIN, 1926 (GORGODERIDAE: GORGODERINAE) FROM THE URINARY BLADDER OF BROWN TROUT, SALMO TRUTTA L.

• Published in: Proceedings of the Zoological Society of London
• Main Author: THOMAS, J. D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1958
• Subjects: Anguilla anguilla; Salmo salar
• Online Access: http://dx.doi.org/10.1111/j.1096-3642.1958.tb00580.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1096-3642.1958.tb00580.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1096-3642.1958.tb00580.x; https://zslpublications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1096-3642.1958.tb00580.x

SUMMARY Brown trout (Salmo trutta L.), salmon parr (Salmo salar , L.) and the eels (Anguilla anguilla (L.)) from certain rivers in West Wales were examined over a period of nearly two years for parasites. Large numbers of Phyllodistomum simile Nybelin were found in the urinary bladder of the trout from the River Teify. P. simile , was not found in any of the 274 salmon parr or 243 eels examined, probably due to an ecological immunity in the former and a physiological immunity in the latter. There was no evidence of a seasonal variation in the occurrence of P. simile in trout aged two years or more. Trout aged four or more years were more heavily infested than young trout and there was no indication of the development of a total immunity with increase in the age of fishes. The life history of P. simile was elucidated under experimental conditions by feeding the trout precocious metacercariae present in daughter sporocysts obtained from the gill lamellae and epibranchial cavity of the freshwater bi‐valve, Sphaerium corneum. The anatomy of the daughter sporocyst, the cercaria, metacercaria and the adult stages are described. The gorgoderid cercariae and the attempts to classify them into groups corresponding to those of the adults are discussed. It is suggested that attempts at discussing the evolution of the cercariae placed in the family Gorgoderidae may be premature in view of the fact that life histories have only been elucidated experimentally for cercariae of the macrocercous, cystocercous kind. The advantages in the life cycle of precocious encystment within the sporocyst are commented upon but it is also suggested that P. simile may have a second intermediate host, possibly the minnow, Pkoxinus phoxinus L. or a freshwater arthropod. The morphological changes that take place during the development of P. simile and their importance in specific diagnosis are discussed. It is suggested that in view of the more readily discernible differences between the larvae, certain larval features might well be used in ...