Discus
In case you need reminding, Discus are Cichlids! In the real world this means they are fishes of changeable behaviour, but also of character and personality. They can on occasion be aggressive towards their own kind and others, mainly when pair bonds are formed, or when territory of fry are involved. If some consideration is paid to this, in cichlid terms they are generally quite mild in behaviour. The main problem is with bullying within themselves. Often, in small groups of fish the individual at the bottom of the pecking order is on the receiving end of a great deal of bullying, which can result in death. To avoid this, I would advocate not keeping the fish in groups of less than 4, with 6+ being an optimum, especially when young. This seems to spread the bullying out, and also increase the confidence of the fish. Size wise, roughly 6-8" round is a good side for an adult discus. Read More