just leave it alone, bichirs can heal them selves pretty quick, what you should do is making sure that it will never happen again. Get the filter setup right.
yea, not trap him, but give him some air. I justy checked and mos tof the red marks are mostly gone already.. im guessing he will be fine..
I am going to go buy a bamboo tube though for him to hide in, i have a cave, but he has a hard time getting in it for some reason... maybe a long bamboo tube wil make him more comfortable and quicken the healing process..
Bichirs are hardy fish and I think your del should be able to survive. Adding another airstone will always help though. I don't think you need to put it right by his face though. If you start to see any open wounds, add a little aquarium salt (not table salt).
My Ropefish got sucked into my filter before right into the Canister bit and he lived the for 2 days and then i noticed he was gone. Hahaha he lived for another year or so. You D should be Fine