Ive had a couple ebjd's and I never had a problem besides aggression towards each other. Id only keep more than one if you get them from the same batch, then theyre fine, but dont mix and match. Besides that though, as long as you keep tabs of your water quality you'll be fine. They grow very fast if you feed them well. I kept most of mine on a brine shrimp, blood worm, and flakes diet and theyre all still alive after a couple years and very big.