It looks like the end was nipped or damaged at some point. It may not turn into a problem though. Keep a close eye on it and take photos regularly so you can see if that damaged looking area near the tip starts to expand up the tail. If you see damaged area expanding then it may indicate an infection setting in. Otherwise it shouldn't be a problem.
I just set Swordtail's timer for his bath and paused it so I could actually fill his soaking bowl up and he crawled over my phone and canceled the timer
Mirage came out of brumation on April 26. He was doing great. On May 2 he started acting funny. We just redid his tank, and he keeps going into one of his hides. He just lays there. He shows no intrest in food. HELP!