i had the exact same experience and agree with the poster above. Take a pair of tongs and wiggle a suitable sized piece of food near his mouth, gently brushing the whiskers. after a few attempts he will grab it. Most people say tigs are inactive, but remeber they are nocturnal. If you observe at night they will be free swimming and looking for food. use the tongs to get him healthy and then feed with the lights off or at night. Now my tig is the most agressive feeder in the community and bullies my dats. Also agree with the prawn stuffed with massivore comment.... you will get great growth rate...patience is the key with tigs..
