Well i just ask them, and aparntly they get kinda bored so they play tag, but to use it looks like niping.
some fish like to eat the slime coat.
some fish are just leting the othere fish know that they are boss.
Boy and girl fish get to know each othere.
Some fish are just meaner then otheres.
I cant faithfully answer this one, but here is what happened to my fish:
I have 5 distichidus Affinis (tetra family). I have SEEN them nip themselves alot (male/female thing cause it only occurs on 3 fish, the other 2 are left alone). ANYWAYS, I notice if I dont feed them cichlid excel pellets (their favorite), they must get hungary. I would notice bite marks on my tinfoils tails and some other fish as well. HOWEVER, if I feed them well, there is no fin nipping. So maybe your fish are just hungary?
Its not an aggression thing with the affinis. If another fish looks at them, they swim away fast!