Pacu

Water parameters

Minimum tank: 2000 L per individual at harvest size.

Feed and growth

Feed protein

28% target

Daily feed (warm)

1.20% of body weight

Daily feed (cool)

0.50% of body weight

Max density

35 g per litre

A 3500 g adult eats about 42.0 g of feed per day at optimum. 10 fish at adult size: ~420 g daily.

Legality

Rules vary by jurisdiction and change over time. Verify with your local fisheries or wildlife authority before stocking.

Unlisted jurisdictions default to "check local regulations".

Origin and habitat

Pacu is a common name for several round-bodied South American fish in the family Serrasalmidae, the same family as piranhas, but pacus are peaceable plant-eaters rather than predators. This entry centers on Piaractus mesopotamicus, the pacu or pacu-caranha of the Paraguay-Parana basin, from northern Argentina up to the Itaipu region; close relatives sold under 'pacu' include the red-bellied pacu or pirapitinga (Piaractus brachypomus) and the larger tambaqui (Colossoma macropomum), which are separate species. Pacus are known for flat, human-like molar teeth used to crush fruits, nuts, and seeds gathered under flooded forest in the wild, making them largely frugivorous omnivores. P. mesopotamicus reaches about 70 cm and roughly 20 kg, while the tambaqui grows larger, to about a metre and 40 kg. The flesh is firm, mild, and somewhat fatty, prized in Brazil and neighboring countries. Brazilian production of these serrasalmid 'roundfish', pacu, tambaqui, pirapitinga, and their hybrids, runs to around 143,000 tonnes a year, and the species have been moved to tropical regions worldwide.

Climate and outdoor ponds

Climate

tropical (needs warm water year-round)

USDA zones

10–13 (winter low around -1°C or warmer)

Heating needed

yes

Cooling needed

no

Care notes

A warm-water food fish well suited to tropical aquaponics, especially in South America and tropical Asia. Pacu do best around 25–30°C; P. mesopotamicus is hardier in the cold than most tropicals, tolerating water down to about 15°C but stopping feeding below 18°C and dying below 12°C. Growth is fast in warmth, reaching 500–1.5 g in eight to twelve months on a pellet of 28 to 35 percent protein, with feed conversion around 1.3 to 1.8. The frugivorous, plant-leaning diet is a real plus for integrated systems: pacu readily take fruit, seeds, vegetable scraps, duckweed, and surplus plant biomass from the grow beds, trimming pelleted feed costs. Stocking runs 15 to 30 g/L, and the fish are social, doing best in groups of three or more. They tolerate moderate water quality, including low oxygen. The main caution is size: pacu grow large and adults need a lot of volume, though most growers harvest at one to two kilos, well short of maximum. Where colder seasons limit pure pacu, Brazilian farmers cross female tambaqui with male pacu to make the fast, robust hybrid 'tambacu'. Pacu are regulated as potentially invasive tropical fish in some places, prohibited in parts of the US and across Australia and established as invaders in Puerto Rico, so check local rules. Fingerlings come from hatcheries in South America and some US suppliers in Florida, Hawaii, and Puerto Rico.

Further reading

• Aquaponics water chemistry: balancing pH for fish and plants
• Fish for aquaponics: tilapia vs everything else