hello,
yes, a picture would be necessary to come closer to a useful conclusion.
There are some possibilities that could be the reason for abloat - any of them could be deadly, any of them would be harmless. Generally bichirs aren't as susceptible to the common bloat that is killing so much fish in keeping - common. But there are exceptions ...
Otherwise bichirs sometimes tend to overfeed themselves. Inthe most cases that will not be dangerous - but i lost a senegal after doing this over many months constantly. my other bichirs also tend to mutate to ball-like beings, but without damage. Here is a pic to show:
Another reason could be the eating of gravel while eating the common food. Normally bichirs are smart enough NOT to do so - but there is no garantee. It is not possible to say anything about the outgoing of those event.
Last not least the most dangerous and most common reason of bloat related to bichirs: A damage of the LUNGS! Yes, you've read it right: Lungs. Bichirs do have a pair of gills (functional & necessary but less powerful - not enough to survive only with them over few hours) AND functional lungs (in older literature and some not actualized publication these lungs will be called swim-bladder). In cases of breath air in the tank that would be too cold or anthing else these lungs could be ignited - similar like it could be happen all other beings. A pneumosis has a letal effect to bichirs in the most cases!
Finally a word to the bichir's lungs: They are much more powerful than those of the most salamanders!
Remember: Help us with a pic to do a diagnosis!!!
Greetings
Uwe