What you may be observing is young fish, or fish that are in no way conditioned to breed hence the "peacefulness"....
My avatar and his mate got along famously in the spawn tank...Spawned once before with barely a scratch..I returned them to the spawn tank a month later and stll, the mellow attitude..They ate together, swam together etc...After day 3, still no spawn, but no fights either...This is where I made the mistake. Instead of removing them like I should have, I became complacent and let my guard down...The female was starting to get antsy, full of eggs and wanting to breed...Doofus had yet to figure it out...A few nips a bit of chasing...A good sign actually...Then (by what I can only figure was shear desperating to drop her eggs) she got extrememly frustrated and litterally tore his fins almost completely off...His fins were actually shorter then the females...Every fin including his tail...It has take a month for them to become even marginally longer then the females...He looks like he has a brush cut...Luckily I was home and removed him to a quarantine for the next 2 weeks...It will probably be another month before I can even think about spawning him again...
Although I have no actual data, I have observed that aggression is more prevalent in the sexually mature females then the sexually mature males...Although the same age chronologically, I think the females mature at a faster rate then the boys...This is probably accurate up until 6 or 7 months of age, where the boys seem to catch up to the girls, switching roles thus making the females more submissive...
One quick option (although ugly) is to fashion a basket made out of plastic canvas...Make it higher then the water line and it works quite well...Be sure to put a top and bottom on it...It is durable and will keep everyone safe until you can make other arrangements...
Good luck
