To the best of my knowledge, the Arsat 30mm f/3.5 fisheye was only made in the Pentacon-six and Kiev-88 mount. But it was sold with a Pentacon-six to Pentax 645 adapter (also Mamiya 645). If this is the case with your lens, you should be able to remove the adapter by turning the breech ring of the adapter.
However, this lens was modified by several 3rd parties to fit other cameras, primarily the Hasselblad F series. In this case, the mount was remove and replaced with a custom part that would fit the desired camera.
Depending on which version you have, accessing the screw will be different. A picture would help.