Gravel is not the only natural substrates in their habitat. It varies from sand, gravel, rock, mud or decaying vegetation or mix of 5. Mostly muddy sand with decaying vegetation. In open areas or in deeper areas where bichirs were found. It's is usually sand with rocks and few vegetation to none at all or some driftwood. While those that are found in the edge of the river or lakes or in shallow areas. The substrates are usually muddy sand, sand with rocks, gravel, or decaying vegetation with plenty of of plants covering the area. A good example of this area is the area where polypterus mokelebembe and polypterus palmas palmas are caught. It's also the reason why these two species of bichirs are harder to find in the wild. Due to the thick layer of decaying vegetation and plenty of plants cover and a muddy sandy substrates. That once you step in and catch them, the water becomes very cloudy with brown sediment.
. As i said i hold them since years on gravel. If he eats it and dies, so be it. I don´t support an animal that is to dumb for it´s own evolution. But so far, they are not. They do fine and never had any problems.
