http://www.monsterfishkeepers.com/forums/threads/tigrinus-behavior.660632/ perhaps bears some relevance to the topic of what to feed a tig.
I went looking for that post yesterday when I first saw the op mention prawns. Ive avoided those items at all cost with mine and its growing nicely. Mine enjoys tilapia, bloodworms, and sinking carnivore pellets.
Comanswoodwork reports good progress while avoiding prawns. Post #9 in this thread:
http://www.monsterfishkeepers.com/forums/threads/new-tigrinus.666477/#post-7491648

Sometimes it just doesn't work out the 1st time. My 1st tig, at 3-4" died from bloat (market prawns?), the 2nd one bought at the same size grew to 22" and ate pellets. Live and learn, it's sucks, but many of us learn from expensive mistakes. It burns right now, but you'll be ok buddy!
Alleged prawn-induced fatal bloat: post #5 by 888fish http://www.monsterfishkeepers.com/forums/threads/clown-loach-toxic.667199/
The main diet is tilapia smelt and massivore I do feed shrimp once in a while but it doesn't seem to be a favorite for my fish