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A Basic Anatomical Structure and Dissection techniques for Cownose rays (Rhinoptera bonasus)

The cownose ray, Rhinoptera bonasus, is currently listed as vulnerable and threatened species by the IUCN Red List due to overfishing and bycatch in worldwide resulted declines of the steep population declines of 30-49% in only 43 years. We aimed to present suitable dissection methods for a necropsy of cownose ray with a large, rhomboid-shaped wing-like pectoral disc and compressed dorsoventrally using a specific approach to observe external and internal anatomy. The fish were obtained from a public aquarium after natural death and were dissected with four incision area to open chondrocranium, gills, pericardial cavity and pleuroperitoneal cavity. The dorsal surface of the body is completely naked and smooth, greenish-brown colored, in contrast the ventral surface of the body is white. The liver fills most of the pleuroperitoneal cavity and covers the esophagus, stomach, duodenum, valvular intestine, spleen, kidney and uterus. The valvular intestine or spiral valve is one of the largest organs of the digestive system. In most rays, only the left ovary is developed and functional; therefore, the ovaries of the specimens are located on the left to the median line, close to the cranial end of the pleuroperitoneal cavity, and caudal to the stomach. In conclusion, the presented dissection techniques will enable to examine of the external and internal anatomy of cownose rays and will contribute to a suitable approach to organs.