Thank you for contacting Healthcaremagic. I have gone through your question and understand your concerns. Masturbation itself does not cause any harm. It is similar to sexual intercourse with partner. Penis does same thing in folded palm what it does in vaginal containment. So, nothing like excessive for masturbation. There are structures like prostate and bulbo urethral glands (Cowper’s glands) in the way of your urine tube. They secrete mucous like fluid. When you void urine, this mucous like fluid (fishy smell) do comes with it. (It is not semen). No need to be worried about for it. This is absolutely normal body response. This suggests that your sex organs are working normally. Wish you good health.