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Vol. 11 Núm. 1 (2022)

Ascocotyle patagoniensis (Digenea: Heterophyidae) from the silverside Odontesthes argentinensis (Atherinopsidae). The bulbus arteriosus as an optimal ecological niche for this parasite species

mayo 12, 2024


Several biological and morphological features of the parasite and their hosts may be determinants for the dimensions of the helminth niche. Helminths cause tissue damage to their hosts by either mechanical action or secretion of toxic substances. Metacercariae of the Ascocotyle genus encyst in different tissues on their fish hosts. In this work, metacercariae present inside the bulbus arteriosus from the silverside Odontesthes argentinensis on the coast of Bahia Blanca, Buenos Aires province, were identified as Ascocotyle (A.) patagoniensis based on morphological and molecular analyses. In addition, parasitic indices are related to the fish condition factor, and the host inflammatory response to the presence of metacercariae is described. The prevalence of A. (A.) patagoniensis in male silversides was 100% (n= 15), and 92% (n= 25) in females. Most of bulbs presented between 20 and 40 cysts. Six individuals harbored more than 120 parasites and the maximum recorded value was 226 metacercariae in a single bulb. All metacercariae were alive and encysted at the study time. Each cyst contained only one metacercariae. The bulb distal area towards ventral aorta was the most densely parasitized and probably the site where infective cercariae first arrive. A discrete or almost inapparent cellular inflammatory infiltrate surrounds the metacercariae forming a thin connective tissue envelope weakly supporting cysts adhered to the internal tunic of the bulb. The absence of coronary irrigation both in the tunica media and the internal trabecular lamina of the bulb could explain the low fish immune reaction. It is suggested that the silverside bulbus arteriosus represents an optimal ecological niche for A. (A.) patagoniensis metacercariae.


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