Piaractus brachypomus (or Colossoma bidens, a synonym that used to be very popular) is an Amazonic pacu, a close relative of piranhas and silver dollars. As with a number of other closely related species, P. brachypomus is often referred to as the red-bellied pacu. This has resulted in a great deal of confusion about the nature and needs of all the species involved, with the reputation and requirements of one frequently being wrongly attributed to the others. An unambiguous name for P. brachypomus is pirapitinga.
Overall size
P. brachypomus can and will grow quickly under favourable conditions. The overall size to which it can grow remains a matter of considerable debate and no small amount of confusion. Much of the confusion stems from the fact that one species can and often is easily mistaken for another, and the size attainable in captivity is usually less than the size attainable in the wild. P. brachypomus is a comparatively smaller species. However, it can easily outgrow the majority of home aquaria: they are strong and robust fish which need a lot of swimming space and make very heavy demands of the filtration system.
Diet in captivity
P. brachypomus is mainly a herbivorous species, but, in fact, it's truer to say that it is an opportunist feeder. Stomach analyses of wild specimens show it to be primarily a herbivorous species, feeding on fruits, nuts and seeds. It is an opportunist, though, and also takes insects, zooplankton and small fish. In the aquarium offer, it a varied diet consisting of quality dried pellets or floating sticks, along with plenty of fruit and vegetables. Spinach, lettuce leaves, and fruit and vegetables such as apple, banana, peach, grapes, courgette, peas, cabbage and carrot all work well. They will also sometimes "snatch" floating food, which results in a lot of splashing and makes a lid essential. In captivity, it is inadvisable to keep this species with anything small enough to be regarded as food, though they are usually safe around larger fish.
In aquariums
At larger sizes, the P. brachypomus needs a correspondingly large tank to thrive in captivity. The temperature of the water in which they are kept should be within 78–82 °F (26–28 °C) and the system should be well filtered and oxygenated. Larger P. brachypomus are sometimes classed as "monster fish" and find a place in aquariums which house other large fish. They tend to be timid and retiring and will retreat to cover if they feel insecure. Some squabbling may become apparent if they are kept in a group.It can take a lot of time for them to get accustomed to the aquarium, and may try to jump out frequently.
