If I'm hosting my own bare git repo, I can go into it and run the following command to make the 'develop' branch get checked out by default when cloning:
$ git symbolic-ref HEAD refs/heads/develop
Unfortunately, when I go into the fisheye bare repo (I'm running it on Linux) and do the same thing, 'master' still gets checked out by default when I clone. I've also tried the various types of re-indexing after doing so, but it doesn't work.
I actually got this to work once briefly, but I was so frustrated at that point that I don't really know which steps caused this to happen, and I can't reproduce it.
I've also tried 'git remote set-head origin develop' from the client and then pushing, but that doesn't seem to help. It's one of the things I did the time that it worked, though.
I'm running Fisheye 2.7.8, and I'm using a repo I created myself (carefully converting from subversion) and am pushing (with --mirror) up to a bare Fisheye-managed repo.
This is not currently possible through the FishEye UI. You can go directly to the bare git repo that is managed by FishEye if you have access to the FishEye server and use git symbolic-ref as you have described. Any clones done after that will default to the develop branch.