It all depemnds on tank size, other fish in question, and remeber that every fish even of the same sp can have very different tempraments. Jardini's are very likely to snap in smaller tanks and undecorated tanks. Paricualy with tankmates who share the upper water coloum with them, sayin that with signifigant cover and hiding places bichirs are a better choice of tankmates, and they can easiely defend them selfs. in most case's aggression wont come out until atleast 6" with a jardini but from then on you will need to keep a verry close eye on your tank and be prepared to move fish if needs be. just my opinion..