The tambaqui (Colossoma macropomum) is a freshwater fish of the subfamily Serrasalminae, family Characidae. It is also known by the names black pacu, black-finned pacu, giant pacu, cachama, gamitana, and sometimes as pacu (even though pacu is a different species, smaller than tambaqui).
The tambaqui is the largest characin of South America. The tambaqui is found in the Amazon and Orinoco basins in its wild form. However, its pisciculture form is widely distributed in South America.
It is similar in shape to the piranha and is sometimes confused with the carnivorous fish; the pacu is tall and laterally compressed with large eyes and a slightly arched back. Body color is basic black to gray with spots and blemishes in its mid body. All the fins are black and the pectoral fins are small. Around 10 percent of a tambaqui's weight is fat. The world record recognized by IGFA belongs to the Brazilian Jorge Masullo de Aguiar with 32.4 kg.
This species is usually solitary. Adults stay in flooded forests during the first 5 months of flooding and consume fruits and grains. Young and juveniles live in black waters of flood plains until sexual maturity. The tambaqui feeds on zooplankton, insects, snails, and decaying plants. Research has indicated the species plays an important role in dispersing seeds from fruits.
Relationship to humans 
In Thailand this fish, known locally as Pla khu dam (ปลาคู้ดำ), was introduced from Hong Kong and Singapore as part of fish farming projects, but has adapted to local conditions and thrives in the wild in some areas.
- Froese, Rainer and Pauly, Daniel, eds. (2007). "Colossoma macropomum" in FishBase. July 2007 version.
- Cressey, Daniel (2011-03-23). "Fruit-feasting fish fertilize faraway forests". Nature News. Nature Publishing Group. doi:10.1038/news.2011.177. Retrieved 2011-03-23.
- Yong, Ed (2011-03-22). "Vegetarian piranhas are the Amazon’s champion gardeners". Discover Magazine blogs. Kalmbach Publishing. Retrieved 2011-03-23.
- Anderson, J. T.; Nuttle, T.; Saldaña Rojas, J. S.; Pendergast, T. H.; Flecker, A. S. (2011-03-23). "Extremely long-distance seed dispersal by an overfished Amazonian frugivore". Proc. R. Soc. B (The Royal Society) 278 (1710). doi:10.1098/rspb.2011.0155.
- Colossoma macropomum introduced to Thailand