It may still be a little cool. I'm at our North Carolina home, and it has been cooler in March than it was in February. Our ponds in this area are probably still in the 50s.
I pretty seriously doubt they died. I've stocked a lot catfish of that size over the years, and I don't think I've had very many mortalities.
I wouldn't be too concerned until your water gets into the mid to upper 60s. Then a handful of food late each afternoon should get a few coming in. Then it soon should be a feeding frenzy.
At that size, the pellet size shouldn't make much difference. And catfish aren't real fussy about the feed they will take.
Good luck,
Ken
