Thymus is considered a key component of the vertebrates' immune system. It is an organ that is only found in these animals whose development may be accompanied through the evolutionary scale, being considered as a facilitator and regulator in the interaction of lymphoid cells and lymphoid organs. In this study not only a morphological but also functional homology were demonstrated, in that it affects the immune system, of the humans and teleost fish thymus. The material of study was composed of the thymus tissue samples of humans who were donated by the

Fungal infections that affect marine mammals, like most fungal infections, can be secondary to environmental stress or other infectious diseases. This article describes a case of pulmonary infection by Aspergillus spp. in a specimen of Pontoporia blainvillei found dead near the town of San Clemente de Tuyu and near the bay of Samborombón, Buenos Aires, Argentina. The lung was collapsed with necrotic foci, fragments were collected, fixed in 10% formalin and submitted to histopathological examination. Microscopically, a marked change of the pulmonary architecture was observed, with total alveolar collapse, extensive necrotic areas, where septal hyphae were observed weakly, when stained with H-E and clearly evidenced with Grocott staining. Since the potential causes of immunosuppression were not evident, the authors consider it probable that infection by Aspergillus spp. was established in the lungs that presented a primary, possibly bacterial pneumonia, as a result of some degree of immunosuppression.

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Lymphocystis disease has been reported worldwide in several species of freshwater fish and marine fish, naturally infected in the wild environment, or in intensive crops in farms. Nodular warty lesions of irregular surface were observed in the tegument and fins and mouth in a species of croaker (Micropogonias furnieri) caught in Cassino beach Rio Grande RS, Brazil and flounder (Paralichthys orbignyanus) caught in the city of San Clemente, Argentina. The skin lesions fragments were fixed in 20% buffered formalin, and the histological sections were stained with hematoxylin and eosin and Periodic Acid-Schiff (PAS), where microscopic alterations were visualized in the form of hyaline capsule with small basophilic structures in nodules and fibroblastic cells proliferation. The reported cases were based on the disease macroscopic findings characteristic of a lymphocystis disease, along with the histopathology, which confirmed the presence of the disease in the analyzed tissues.

During the last two decades, the implementation of histochemical, immunohistochemical, electron microscopy, and recently developed molecular techniques has greatly contributed to our knowledge of skeletal muscle, both normal and sick. This article reports the presence of muscular atrophy and fibrosis in Xiphophorus maculatus from an ornamental fish farm. We do not know the origin of this muscular pathology and the purpose of this work is to summarize some of the findings with optical microscopy and electron microscopy shared by all. Although we cannot establish the etiology of this atrophy, we will try to correlate the ultrastructural alterations with the muscular histopathology. Muscular atrophy is a pathology characterized by loss of normal muscle mass. It is caused by a decrease in the total number of muscle cells or by a substantial reduction in the substance of individual muscle cells. It is likely that the cases reported here represent a pathology involving causes concurrent with nutritional problems and disorders of muscle innervation. Therefore, future studies should investigate further about the potential of neurodegenerative disorders. Several experimental models can use muscular atrophy and are suitable for investigations of the underlying mechanisms of this pathology.