Dear user, Thanks for writing to HCM. During sexual arousal the pre ejaculatory fluid comes out. This happens to you while watching porn. There are structures like prostate and bulbo urethral glands (Cowper’s glands) in the way of urine tube. They secrete mucous like fluid. It does have fishy smell but it is not semen. Nothing bad. This is as simple as salivation occurs when you think or see your favorite food! Absolutely normal body response. No need to get worried for this. Amount may be variable. This is not a disease. No medicines for it. Solution is psychological counseling. Relax and have a healthy sex life ahead.