I'm not sure I understand your question. Also do you mean Fort Jesus in Mombasa, Kenya? As far as I'm aware the Old Fort of Zanzibar in Stone Town is not called "Fort Jesus."

It's not a specialty of mine but both Mombasa and Zanzibar were ruled by the Sultanate of Oman, which dominated the east African slave trade. I would look for more sources on that topic, though I'm afraid I can't point you to any in particular.