Syno's are territorial to some extent, unless they are social species like petricola or multipunctatus. They tend to pick a spot and chase other fish out, but most aren't aggressive toward other species of fish. I've kept Syno's for years w/no problems with other fish. In a 55 containing an angilicus, a eupterus, and several decorus, they occaisonally argued, but no real damage was done. They got along fine with the other residents.