Hello Cohazard,
there goes the gossip that gravel may harm bichirs ... bull...t!
I've lost only two bichirs over the years - a endlicherii caused by a secundar infection (bacteriosis) after the affection with Macrogyrodactylus polypterii ... and a senegalus after constant overfeeding (i think anything was wrong with his mind) - the section didn't show any gravel in his stomach or elsewhere ...
Gravel do have mostly positive effects:
It helps to filtrate the water as a medium for "good" bacteria ...
There's the possibility to plant the tank - also good for cleaning the water and splitting up bad substances like nitrit ...
And finally it looks good!
I'm wondering about those emergency-room-like tanks ... it seems to me unnatural. But that's my opinion ...
Greetings
Uwe