Bichirs when they are new to a tank will often go on eating strikes and not eat. Sometimes it lasts a couple minutes to a couple weeks. I'm not sure if all you've fed are flakes, but flakes are both uninteresting and not filling for bichirs. That's most likely why they haven't really eaten for you yet. I would suggest going to the store the next chance you get and get some sort of pellet that has around a 35%-50% crude Protein. Once you have a pellet that they will eat, I would suggest tilapia, or even more Hikari pellets such as cut up massivore, sinking carnivore pellets, bottom feeder tablets, etc.., Once you start introducing pellets and tilapia they should start eating and bulking up in no time.
