Odds are those minnows have been either been held in a baitfish tank, probably concrete, for several months, haven been captured during fall, or they have come from a fish farm in the south recently. Either way, they are distressed.
Fathead minnows held locally for weeks or months have likely not been fed, have been kept crowded and decline a little bit each day. At some point, they are too weak to sustain more handling and transport.
If they are coming from a fish farm in the south, they've been captured from a pond, where they likely haven't eaten much during winter months, seined, put in concrete tanks, held, then dipped, loaded onto a truck, hauled for hours, then placed into different holding tanks, then bagged up and hauled to your place.
Losing some of the minnows this time of year is to be expected. It should be skinny, weak minnows. If that's the case, expect some deaths. If they aren't skinny and weak, it could be something else.
Cody has the best idea. Set up a quarantine tank, put the minnows there for a week, and feed to your game fish as needed.
