advice..pbt stopped eating

[bglegs]

I've had him for 6 months and now he's stopped eating.There are no physical signs and no aggression in tank.My other fish are all eating.He's acting listless but doesn't have clamped fins and doesn't hide.I've went through roughly 40 pages on the search button.thanks in advance

 

[TripleT]

What size tank?

What other livestock?

What are your water parameters?

What is your water change routine? When was the last change?

What have you been feeding, and how much? Using supplements?

Is he breathing heavy?

Do you have a QT tank in case you need to use one?

Post pics.