I grew my pair out from babies. I started with 10 and ended up with two, my pair has just spawned and are a little over a year old and around 4.5". Some tell me they are small for the age but they have gone from a 20 gallon initial growout to a 55 to a 1200 gallon pond and then into a 125 and now are residing in their own 120. So I have had the in the largest possible tanks that were within reason for their size. They have always been with other fish, well since they were over 1.5". There was a small time period when they were alone (before breeding) and they went at it. I added other growouts of mine to the tank and thats when they started acting like a pair and protecting each other. A month after that I had eggs in the back corner and they are now freeswimmers! I tell you this all because I think it may help you if you run into agression problems having them as then only fish in the tank before the spawn.