HISTOPATHOLOGICAL LESIONS OF THE ISOPOD Riggia puyensis ON THE ARMORED CATFISH Chaetostoma breve AND Chaetostoma microps (SILURIFORMES: LORICARIIDAE) FROM ECUADOR

Chaetostoma Steindachner is a loricariid genus of suckermouth armored catfish from Central and South America. In a survey on parasites of fish from Ecuador an isopod belongs to Cymothoidae was found. Fishes were collected using a cast net in the Puyo and Bobonaza Rivers (Province of Pastaza, an Amazonian region of Ecuador). Eighty-six individuals of Chaetostoma breve and 122 of Chaetostoma microps were inspected by the naked eye, and only the parasitized were carried to the laboratory for examination. Each of the parasitized fish has a single female isopod encapsulated in the abdominal cavity of the host and maintaining an opening towards the outside through a small pore. The aim of this study was to analyze the damage that Riggia puyensis inflicts on its hosts through the evaluation of histological sections. For this, infected fish were fixed by immersion in 10% buffered formalin, and processed for histological studies.  The samples were sectioned at 3-4 μm and subsequently stained by the Hematoxylin-Eosin and Masson's trichrome. Histological examination revealed local hypertrophia in the skin due to irritation caused by the parasite to the small pore level. In the epidermis, pyknotic cells were observed and loss of the normal architecture with rupture in some sectors of the epithelium. Also, an infiltration of numerous inflammatory cells, mainly lymphocytes, and macrophages, was detected as part of the host's inflammatory response. In the site where the isopod is supported, atrophy in the epithelium of the abdominal cavity wall was observed. Evaluation of histological sections by light microscopy showed that alterations in the abdominal cavity were consistent with a chronic process.