Although I don't think that it is useful that the assignee can only the issues that are assigned to him, you could do this by using an issue security scheme.
Create a new scheme, add the assigned and probably some other user that assigns the issues to the security level and then assign the scheme to your project.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.