fish died

[Link119]

Recently one of my platies died. It has recently been acting lethargic and its tail fin looked like how it is on the pictures. As far as i can tell it showed no other bad signs. What could have killed it?

 

[Fishfur]

Unfortunately there are several things that might have caused it, but lethargy is a symptom common to many illnesses. The fins look clamped, which is another sign of illness, often of ammonia exposure or nitrite exposure. There is really no way now to know what killed this fish, but make sure the water parameters are good, with no ammonia or nitrites.