I have a 400-litre aquarium with mostly Malawi cichlids. Aquarium has been functioning well for three years, and all parameters are good. Low nitrates. I have lost fish one by one over the past several months, but they are always the same species - six red zebras, fully grown siblings about three years old, and four fully grown pink peacocks, all siblings about the same age. I've lost no other peacocks (OBs) or any other mbunas. The tank also contains clown loaches, silver scats, a mono sebae, catfish, all healthy and about the same age - around two or three years. I do have two other red zebras, not siblings of the ones that died, and they are in good condition. My initial thought was that all of these early fatalaties could be genetic, as they should live longer than three years in a system that is well managed, with all fish being fed the same nutritious food. Any thoughts about possible causes will be appreciated.