DOES SIZE REALLY MATTER?
The classification between the Upper Jaw and Lower Jaw Bichirs is not a big thing. This is something that Bichir keepers enjoy in pursuit of the hobby.
Some keepers collect Upper Jaw Bichirs in one tank, and keep only Lower Jaw Bichirs in another. Other keepers would not even care and keep both variants in one tank, so long as the sizes are compatible.
Does it matter? Not really, but knowing the difference between the two is something that’s nice to know, especially among Bichir keepers.