I been keeping my 18"-20"+ bichirs with some smaller 7" bichirs for many years and the 7" have not been eaten. I even got some aros, knifefish and snakheads that are 15"-20".
My tank is 54g (5ft) sen was the first bichir in the tank and my endi is fairly new
cichlids there currently with are a oscar which im growing out he'll move soon to a 100g
a brazilian earth eater,
festivum,
severum,
blue acara,
spotted climbing perch,
a pair of convicts breeding going to be moved to a breeding tank,
a syno,
and bristlenose
Considering that he asked about 20cm+, the minimum size he's asking is just about an inch bigger than what I have, so I think it's relevant.
I've seen a large Endli (16"-18") with some smaller Sens (8"-10") before. As for your Cichlid stock, they all seem pretty peaceful, except for the Convicts (which you alraedy stated that you're moving). Will you be moving the Endli into the 100g or do you plan on keeping the Polys together long term?
i would like to keep the polys together if possible and i would like to add an ornate at some point whether there moved to a 100g with my oscar or not but i would like my bichirs to stay together
When bicirs hatch out the go thru a larval stage what you are seeing are the external gills they are born with they will usually be reabsorbed into the body