Hydra and Fuchsia are both operating systems that use Capability-based security. Hydra would have been one of the very earliest ones, while Fuchsia is a very new one. There have been many others in between, like KeyKOS or EROS, as well as use of capabilities in "normal" operating systems, like FreeBSD's Capsicum, or arguably even just passing file descriptors over Unix sockets with SCM_RIGHTS on any POSIX system. There have also been capability-based programming languages like E and Pony, and capability-based network protocols like CapTP or (my own) Cap'n Proto. So it's unlikely that the designers of Fuchsia directly based it on Hydra, but there was probably indirect inspiration, yes.