That's terrible

I get really sad imagining those poor guppies falling out of the bag

But to the business, Nabi is right in every sense. Feeder fish should in general be avoided, just for the reason that they're hard to cure and keep alive the first weeks! So I'm pretty certain that the one you have there might be taking his last breath

And it's probably from all the diseases it's been exposed to while staying in the pet shop, and from the stress of being moved to a new place. But I don't know... you could try adding a bit of medical aquarium salt to his tank and see if he gets better! Keep an eye on the water quality too
