I can't find my catfish!!! again?

a few days ago i transferred my chocolate catfish to my goldfish tank because the tank he was in was too small for him. i figured it'd be ok for both species. i saw him hiding behind a plate like decor i have in there the first 2 days and then i can't spot him anymore. there are lots of more hiding places in there and i thought he just found a good one (he hides so skilfully he used to do that in the old tank) but now a few days have passed and im beginning to get worried. he is nowhere to be found and there is noway the goldfish would've ate him. any idea what could've happened?