A Sight for Sore Eyes: Diplostomum and Tylodelphys in the Eyes of Fish

ylodelphys Diesing, 1850 and Diplostomum von Nordmann, 1832 are trematode parasites of Order Strigeatida, Family Diplostomidae, which co-populate the eyes of teleost fish in the metacerarial stage. Fish, infested by these species, develop impaired vision and morbidity of the eye eventually developing a condition known as 'pop-eye'. Fish with heavy infestation, called diplostomiasis, lose weight and experience anterior traumas due to impaired vision failing to locate food and striking rocks or other objects. Field and Irwin (1) cite a number of authors who suggest "infection with Diplostomum spp. metacercariae results in increased predation by birds and fish, and an altered feeding behaviour in heavily infected fish populations". The effects are more pronounced in farmed fish than wild populations. A broad world spread of records is provided (2). Field and Irwin (1) point to the vast body of published information on Diplostomum spp., up to 1994, and since then, publications concerning Diplostomum spp. have not abated. Researchers go some way to providing worldwide records of occurrence of diplostomids, but mostly in the northern hemisphere (3). They did distinguish 19 newly delineated species out of a previous count of 33 species; however as is commonly the case, sampling effort appeared to play a role in species delineation. This study concerns only the metacercariae of two species, and the only species of Tylodelphys recorded was T. clavata. Diplostomum and Tylodelphys inhabit the eyes of freshwater fish throughout the world. However, the phylogenetics of two genera remains problematic, and the role of morphometrics is re-asserted. Incidence of Diplostomum ssp. and Tylodelphys clavata in Perca fluviatilis in Ireland was recorded with age of the fish hosting the parasites. A generalized linear model, GLZ, was applied to T Iranian Society of Parasitology http:// isp.tums.ac.ir Iran J Parasitol