Raising fish through aquaponics can cut your costs well below what traditional fish farming requires, and the system uses far less water, making it a genuinely eco-friendly choice. Pacu bring a number of advantages to an aquaponic setup. Below you’ll find a rundown of what makes this fish work well in aquaponics, along with a few of the challenges you should plan for.

Information for Pacu Aquaponics

Pacu are omnivorous fish native mainly to South America, and the name covers several species within the serrasalmid family. They’re close relatives of the piranha and are sometimes nicknamed the “vegetarian piranha.” Despite the family resemblance, their teeth look nothing alike: a pacu’s teeth are flat, squared-off, and oddly reminiscent of human teeth, while a piranha’s teeth are thin and razor-sharp. Their jaws are also structured differently. Diet is another key distinction — pacu mostly graze on plant matter, while piranha are primarily flesh-eaters. Pacu can reach an impressive size, growing up to roughly 3.5 feet long and 88 pounds. Success with pacu in an aquaponic system starts with understanding these basic traits.

Different Pacu Species

Red-Bellied Pacu

Young red-bellied pacu look a lot like red-bellied piranha, though the resemblance fades as they mature. This species grows quickly and can reach up to 24 inches, so it needs a spacious tank — plan on roughly 250 gallons at minimum — along with strong filtration to keep the water quality stable. Flake food works for younger fish, but as they grow you’ll need to shift toward pellets to support continued development. Because they’ll happily eat live vegetation, keep them separate from any planted tank. Their size also makes them a danger to smaller tankmates even though their diet leans herbivorous, so this isn’t a great choice if you’re new to fishkeeping.

Black Pacu

The black pacu ranks among the largest characins found in South America. As its name suggests, it’s dark in color, and it can grow to about 3 feet and 55 pounds. Feeding this fish is straightforward, but its sheer bulk demands a large tank, which can make it a tougher fish for a first-timer to manage.

Feeding the pacu

Because pacu are omnivores, feeding them is fairly simple — they’ll accept most food types. Offering a varied diet supports better growth, and plenty of suitable commercial foods are widely sold. In the wild, their diet centers on plants and vegetables, and they’ll happily eat greens like spinach in captivity too. They’re capable of eating live fish, but this isn’t advisable since it can introduce disease into the tank. One option is feeding them the plant waste from your aquaponic system. Stick to one feeding per day — feeding more often just adds to waste buildup and raises the risk of overfeeding. Pacu also instinctively seek shelter since they’re wired to watch for predators, so give them places to hide. The shape of the hiding spots doesn’t matter much, but avoid anything with sharp edges that could hurt them; branches or sticks work well. Aim to keep about three-quarters of the tank covered. Skip live plants as hiding spots, since the fish will simply eat them. Good cover isn’t just about comfort — it also supports a stronger immune system and helps the fish resist disease.

Pacu fish temperature

Keeping your pacu healthy means paying close attention to water conditions, especially temperature. They need clean, warm water to thrive, ideally between 75 and 82°F (24–28°C). A thermometer is a must for tracking this consistently, and you may need a heater to hold the temperature steady. One side effect of heating water is reduced oxygen levels, so watch for signs of oxygen deprivation, which can lead to heart trouble and nerve damage in the fish — an air pump with airstones helps prevent this. On the flip side, water that’s too cold weakens the immune system and opens the door to illness, including serious conditions like mouth rot or dropsy, both of which require prompt attention.

Pacu fish growth rate chart

A healthy pacu can reach around 25 inches in length, live up to 20 years, and weigh as much as 48 pounds. Given this rapid growth, a large tank is essential — figure on about 10 gallons of water for every pound of fish to give them room to reach full size. Strong biological filtration is also critical, since like any fish, pacu can’t tolerate spikes in ammonia or nitrite.

Combining Pacu with other Fish

It’s best to avoid housing pacu with other fish species. Their large size puts smaller tankmates at constant risk, since even an omnivorous pacu can pose a threat. These fish generally do best on their own in a spacious tank where they can grow undisturbed.

Pros of Pacu in Aquaponics

Pacu Fish Are Easy to Harvest

Since pacu eat a broad range of foods, harvesting them is relatively simple. It’s a good idea to purge them for two to three days before harvest in a separate tank — given their large size, a dedicated tank makes this process work better and lets their digestive system clear out fully beforehand.

High Growth Rate

Pacu can grow quite large, which makes them a rewarding fish to raise for harvest. A fast growth rate translates directly into a bigger yield.

Cons of Pacu in Aquaponics

Temperature

While pacu can tolerate a range of water conditions and aren’t picky eaters, they do need to stay within a specific temperature band — the same 75 to 82°F (24–28°C) range mentioned earlier. Straying outside that range brings on stress and illness, so ongoing temperature monitoring is a must.

Not Beginner Friendly

Pacu generally aren’t the best pick if you’re new to aquaponics. They need a specialized diet and don’t cohabit well with other species, which adds complexity for a first-time fish keeper.

Pacu fish FAQ

What do pacu fish eat?

Pacu are omnivores and will eat both meat and vegetables, though their diet leans heavily toward plants and greens. In the wild they’re also known to eat nuts. Their sharp jaws let them handle a wide variety of foods.

How big does the pacu get?

How large a pacu grows depends largely on the care it receives. Under good conditions with adequate nutrition, it can reach about 25 inches — a substantial size for most tanks.

How does pacu taste?

Pacu has a mild, sweet flavor often compared to striped bass or rainbow trout.

How long does pacu live?

Given ideal conditions, a pacu can live for up to 20 years and reach nearly 48 pounds as it ages.

Where to buy pacu fish?

Availability depends on the fish hatcheries near you, so pacu can sometimes be tricky to source locally. Buying online is usually your most reliable option, and since the species is commonly harvested, it’s available in most regions.