I looked up the other day and noticed it so like 2 or 3 days now. The desmoni bullies my smaller fish since and the rusty is a female maybe they were fighting each other.
In nature you see this all the time, cichlids lock lips to vie for dominance, test for mate choice etc.
Below are Jack Dempseys from a cenote in Mexico. Almost all males had lip scars, and slight fungal infections on the lips .
My Lepidiolamprologus pair constantly test each other, and their teeth do noticeable damage.