Ovarian prolapse associated with severe granulomatous hepatitis in an adult female montezuma swordtail Xiphophorus montezumae (Jordan & Snyder, 1899)

Introduction - Prolapse through the vent is relatively common in fish. Vent prolapse in fish includes intestinal prolapse through the anal/genital pore and ovarian prolapse through the genital pore. This event can occur secondary to an infectious process or may be consequent to straining from passing eggs or constipation, although predisposing or associated pathological conditions are not frequently determined, especially as far as ovarian prolapse is concerned. Careful physical examination may allow to identify the prolapsed organ, since ovarian tissue usually appears to be grainy with presence of small white to yellow follicles, whereas intestine typically have a smooth surface (Lewbart, 1998). Description of the case - The present case describes an adult female Montezuma swordtail, Xiphophorus montezumae (Jordan & Snyder, 1899), showing a mass protruding from the genital pore, with macroscopical features referable to ovarian tissue. The fish spontaneously died after a fifteen-days period of progressive reduction of food consumption, with moderate weight loss, and it was immediately submitted to necroscopic and histopathologic exams. Post-mortem examination confirmed the ovarian prolapse, associated with a moderate abdominal enlargement. Opening of the coelomic cavity also revealed severe hepatomegaly associated with pale, yellow to tan liver parenchyma and presence of multiple, miliary nodules on the liver surface. Samples of liver and ovarian tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, cut in 5 μm-thick sections, stained with haematoxylin-eosin (HE) and examined by light microscopy. Additional sections were also subjected to Ziehl-Neelsen stain, with (P-ZN) and without (ZN) pre-treatment by a 24 h incubation in 10% periodic acid, which may improve detection of acidfast bacilli in fish. Histologically, liver parenchyma showed multiple granulomas, characterized by a necrotic core, containing eosinophilic cellular debris, surrounded by epithelioid cell layers of variable thickness, with presence of scattered multinucleate giant cells. Multiple granulomatous and pre-granulomatous inflammatory foci were also detected in mesentery and ovarian tissue. Multifocal, mild to moderate acid-fast staining was revealed by ZN, especially in the epithelioid layers, whereas P-ZN revealed higher numbers of intensely stained acid-fast bacteria, with beaded or barred staining, which were found in dense sheets and clumped aggregations within the necrotic core or individually in the surrounding epithelioid cells. A focal aggregation of acid-fast bacteria was also detected in intraovarian fry tissues by P-ZN. Histological and histochemical findings were suggestive of mycobacteriosis, although a differential diagnosis with partially acid-fast, related actinomycetes, such as Nocardia, was considered Conclusions - Multinucleate giant cells, characteristic of mycobacterial granulomas in mammals, have been rarely reported in fish, since the majority of mycobacterial lesions described in fish lack these cells. Detection of acid-fast staining in intraovarian fry tissues is also important, since vertical transmission of mycobacteria has been suggested, and transovarian passage in livebearing fish has been reported (Roberts, 2001; Gauthier and Rhodes, 2009). Pathological conditions associated with ovarian prolapse in fish remain frequently undefined. A unique study in an oviparous species reported the occurrence of egg retention with a egg mass protruding from the vent in a female frogfish Antennarius striatus, associated with an atypical, severe systemic mycobacteriosis, characterized by the absence of typical granuloma formation (Yanong et al., 2003). To our knowledge, this is the first report of an ovarian prolapse associated with severe, multifocal granulomatous inflammation referable to mycobacteriosis in the ovoviviparous species Xiphophorus montezumae.