I don't think there is a plugin integration for Trac in Crucible.
You may want to explore one of the 3rd party integration framworks to achieve this, e.g. Cloudpipes.
This requires that your applications are exposed to the internet though.
Another solution would be to consider migrate your Trac application to JIRA. Then your integration would be right out-of-the box. I don't know if this is applicable at all in your situation but it is definitely soemthing to consider. JIRA will provide the same functionality Trac has and a lot more on top of that!
You can do some integration with Trac, but it will not be as 'deep' as the integration you can achieve with JIRA.
You can index the repository you are doing your development in with FishEye.
Then you can set up a Linker, which will find Trac issue keys in commit messages and turn them into links to Trac.
You won't get any of the issue creation and issue workflow which is possible with JIRA integration.
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