Descriptive osteology of Chondrostoma regium (Heckel, 1843) in Tigris basin

To study the osteological charactrestics of Nazak fish (Chondrostoma regium), the 12 specimens were caught from the Karun, Karkhe and Jarrahi rivers in the Tigris basin by electroschoking device and seine net. After anesthesizing with 1% clove oil solution, then they were fixed in 10% buffered formalin, clarified and stained by alizarin red and alsian blue for osteological examination. Afterthat, the osteological features of this species were described. The skeletal structure of the maxilla and premaxilla, quadrate, symplectic, parasphenoid, basioccipital and urohyal indicated some differences compared to other species in Cyprinidae. In the premaxilla, only an appendage was seen. The Posterior process in the maxilla bone was downward. Anterior part of the parasphenoid bone was narrow and long. Posterior pharyngeal process of basioccipital bone was long, elongate and roughly rectangular in the shape and Ventral masticatory plate of basioccipital bone was big and wide. Anterior part of urohyal bone was narrow, elongate and forked. Quadrate was long and developed and symplectic was roughly long and forked. These traits could be usefull as diagnostics for this species.