
Females frequently use social cues to assess a male's genetic quality. If a male is highly sought after the female perceives him as a desirable partner. Smaller, subordinate males specifically utilize same-sex "flirtations" like pre-copulatory nipping to boost their sexual appeal to females.
in the study it says that it’s because the female fish like behaviors that resemble other female fish, which is usually getting courted by a male in the fish world. So when a male fish is nipped by another male fish, it’s relatable to them: https://journals.biologists.com/jeb/article/216/15/vi/11480/HOMO-SEXUALLY-ACTIVE-FISH-ARE-SEXIER-TO-FEMALES