Tongs in FV has live brine.
Often the fish will have gill parasites. Who know what kind of tank the fish has been in since it was shipped. That can keep the fish from eating even if it is hungry. Recently I had an angel fish in the QT that would not eat more than one brine shrimp, then would only stare at them. I end up doing a FW dip, then started hypo. I think that helped move the gill parasite, it started eating the next day.