No.The police don't have to advise you of your rights. You are referring to 'Miranda' which simply says if you are interrogated and in custody, you must be advised that what you say may be held against you, etc. In your case, if you were in custody on warrants for something else, and they interrogated you on the assault, your rights were probably not violated (you were not in custody on the assault). Additionally, the usual consequence of a Miranda violation is simply that those statements you made will not be used at trial.