I bought 3 Platys a few days ago, yesterday night one of them started to act lethargic. I looked around and saw that his was a common response to a new environment, however this morning when I woke up, i noticed a long stringy thing coming out from its Gill. I'm preparing a small Quarantine tank that I have, but what could this be? The fish is still lethargic and breathing very rapidly. When i went to feed them all, It wouldn't eat. Im guessing a parasite, so i'm going to move the fish very soon.