Increased dietary availability of selenium in rainbow trout (Oncorhynchus mykiss) improves its plasma antioxidant capacity and resistance to infection with Piscirickettsia salmonis.

Salmonid Rickettsial Septicaemia (SRS), caused by Piscirickettsia salmonis, is the most important infectious disease in the Chilean salmon farming industry. An opportunity to control this disease is to use functional micronutrients to modulate host mechanisms of response to the infection. Since P. salmonis may affect the host antioxidant system in salmonids, particularly that dependent on selenium (Se), we hypothesized that fish's dietary selenium supplementation could improve the response to the bacterial infection. To address this, we defined a non-antibiotic, non-cytotoxic concentration of selenium to evaluate its effect on the response to in vitro infections of SHK-1 cells with P. salmonis. The results indicated that selenium supplementation reduced the cytopathic effect, intracellular bacterial load, and cellular mortality of SHK-1 by increasing the abundance and activity of host glutathione peroxidase. We then prepared diets supplemented with selenium up to 1, 5, and 10 mg/kg to feed juvenile trout for 8 weeks. At the end of this feeding period, we obtained their blood plasma and evaluated its ability to protect SHK-1 cells from infection with P. salmonis in ex vivo assays. These results recapitulated the observed ability of selenium to protect against infection with P. salmonis by increasing the concentration of selenium and the antioxidant capacity in fish's plasma. To the best of our knowledge, this is the first report of the protective capacity of selenium against P. salmonis infection in salmonids, becoming a potential effective host-directed dietary therapy for SRS and other infectious diseases in animals at a non-antibiotic concentration.

Relación entre desplazamiento de melanosomas y cambios de color en lagartijas machos: liolaemus tenuis tenuis: un estudio ultraestructural / Relationship between melanosomes displacement and color change in male lizards: liolaemus tenuis tenuis: an ultrastructural study

La mayor parte de los organismos multicelulares se caracterizan por un patrón de color distintivo y, a menudo, particular. Uno de los efectores relacionados con el proceso corresponde a células especiales, los cromatóforos. En este trabajo se demuestra mediante técnicas de microscopía electrónica, que en el dermis de reptiles sometidos a 35§C por 12 min, se produce una fuerte concentración de melanosomas en torno al núcleo de los melanóforos. Por el contrario, a 0§ los melanóforos presentan expansiones citoplasmáticas que contienen numerosos melanosomas. Asociados a los melanosomas en dispersión, se observan microtúbulos. Esta característica permite plantear la posible existencia de algún tipo de relación entre microtúbulos y movimiento de melanosomas en este reptil, cuando es sometido a bajas temperaturas, momento en que se oscurecen. Se destacan también, gruesos manojos tridimensionales de fibras colágenas asociadas a fibroblastos, estructuras, que para algunos autores, representarían un primordio de esclerificación dérmica, fenómeno que predecería a la fase fibrilar de la osificación dérmica o directa. Otro tipo de célula, los iridóforos, contienen placas reflectantes que reflejan la luz en direcciones determinadas