Zachowanie się metacerkarii D. pseudospathaceum Niewiadomska, 1984 i D. spathaceum (Rudolphi, 1819) w soczewce oka ryb oraz reakcje soczewki na obecność pasożytów

The author presents the results of the morphologkal studies on the lens of fish infected experimentally and in a natural way (in the river Vistula near Warsaw) with the metacercariae of both flukes. Basing on this and on the literature data a detailed picture of the pathological changes in the eye lens of infected fish has been constructed, the three development stages being accepted as described by other authors. The mechanisms of the influence of the metacercariae on the eye lens are presented. A particular attention has been paid to the significance of the ontogenetic development and the structure of the eye lens, not considered before, and especially to the fissure in the lens (Fig.). The latter, as a result of the metacercariae feeding on the lens material and distend it mechanically as they grow, is transformed into a chamber filled with a loosened lens material and the parasites. This leads to a deglutination of the lens capsule (sometimes on its entire perimeter) from the internal material. A symptom characteristic of the diplostomiasis in Missgurnus fossilis, observed by the author, consisted in fine folding of the capsule. Other symptoms were: besides the damage of the lens surface, changes in its size, deformations, loosening and sometimes breaking, always on the side of the enlarged fissure. Besides, the author confirms the results of observations of other authors and expresses an opinion that the picture of the pathological changes and the degree of vision impairment is influenced by such factors as the density and distribution (signly or in aggregations) of the metacercariae in the lens, and the place of their penetration and the host species.