Help sexing bichir

[BlacksmithFishkeeper]

Ive seen this cupping behaviour even if the bichir is by itself in a tank full of mature bichirs. Do they swim together - like mating - shaking and sudden burst/darting off?

I have a few ornates and endli and most male flex their anal fins even if not mating.

Yeah, they swim together. The endli pursues the lap and gently bites at it's tale and stuff. Then the lap will reciprocate and try to be near the endli. Endli shakes his tail while cupping his fin near the lap. My endli didn't start doing any of this till I added the lap into the tank