Short communication:A microscopic survey on Epicardial hemangioma-like structure in farmed sturgeon, Acipenser baerii

As the main organ of the cardiovascular system, the vertebrate heart has been the focus of a myriad of morphological, functional, and molecular studies. The heart of fishes has not escaped from this stream of interest, and a wealth of information has accumulated on this subject over the past ۵۰ years (Icardo, ۲۰۱۲). The heart of sturgeons is related to that of other ancient fish and the elasmobranches in that it has a long conus arteriosus endowed with a muscular coat and several rows of conus valves (Icardo et al., ۲۰۰۲). The subepicardium is a thin layer rich in collagen and elastin, fibroblasts, vessels, and nerves (Icardo et al., ۲۰۰۰). Although this constitutes a general description, the subepicardium of the bulbus can be a more complex layer. For instance, it may contain lymphocytes, plasma cells, and dendrite-like cells, and has been implied to be involved in the development of the humoral immune response (Icardo et al., ۱۹۹۹). This is surprising, but it is not an isolated feature in fish. The subepicardium of the sturgeon contains thymus-like tissue (Icardo et al., ۲۰۰۲) which has been implicated in the establishment and the maintenance of the cellular immune responses.