Pacu Fish Care in Captivity with Complete Facts

Pacu fish are one of the most misunderstood species. Be it their looks or behavior. On the other hand, their demand in the global hobby circle is rising. Many countries trade them for consumption.

A lot of fish lovers have questions about this astounding aquatic beauty. But there is mixed information available. A few fish owners were unaware of what they purchased until reality hit them. However, sellers insist they give enough warning and education before selling it.

It’s time to bridge the gap and avoid disconnects. This article aims to provide all information about pacu fish, their requirements, facts, and myths so we can appreciate them in toto and make responsible decisions about them.

What is a Pacu Fish

It is a generic name that refers to various tropical freshwater fishes in the serrasalmidae family. It breaks the first myth, where people use the term pacu fish for a specific variety they have/know of without knowing its correct name.

The taxonomy (classification) of pacus has changed over the years till all of them were placed in the serrasalmidae family. The family includes pacus, piranhas, and silver dollar species.

Their differentiation is according to teeth and eating habits. Within each of them, there are further varieties and sub-types.

To date, the ongoing classification of pacus is debatable among ichthyologists (experts in the study of fishes), as many species have similar characteristics falling under different categories.

Pacu Fish Vs. Piranha Fish

Second myth – Pacus resemble the piranhas in appearance, especially in juvenile years. Many stores sell them interchangeably due to incorrect identification.

The main differences between the pacus and piranhas are listed below.

Characteristic	Pacu Fish	Piranha Fish
Diet	Majorly Herbivore, opportunistic Omnivore	Carnivore
Teeth	Strong, square, human-like teeth to crack and grind hard food grind hard foods into finer morsels before swallowing.	Sharp, triangular teeth to tear flesh
Adult Size	Up to 3 feet long  (variety-wise)	Up to 13 inches long
Popular Generic Name	Vegetarian piranhas (applied to any variety)	NA

Origin and Habitat

Pacu fish hail from South America. They thrive in tropical freshwater rivers, lakes, ponds, and flooded plains. They are also found in brackish waters.

The name pacu in the Brazilian languages of Tupi and Guarani means quick eaters. It could be due to their:

• Speed in cracking nuts/fruits and seeds and eating them.
• Readiness to accept any food.
• Huge appetites to sustain their large bodies.
• Adaptability in captivity. While many fishes take 2-3 days before accepting food in captivity, pacus eat food within a few hours.

Being tropical, they like warmer waters. One of the species (small-scaled/parana river pacu) can survive in temperatures up to 15 degrees C. At 18 degrees C, they stop eating and lose weight.

Due to high demand, some countries (like Papua New Guinea) introduced them as non-native species in their freshwaters. Pacus survived and spawned in varying environments by adapting to whatever was available.

International fish trade also led to their presence in non-native countries. Pacus generally grow large. The release of overgrown home aquarium pacus into the wild by a few hobbyists led to their surprise appearance in freshwaters of a few countries.

Pacus are considered invasive species (species that threaten other native species) in many countries. All pacus (any age) love hiding and playing around plants and rocks.

North America has a high pacu fish trade for the hobby circle. South America has a high demand for consumption. Besides, Europe (Denmark, Paris, Russia, Romania, Poland, and Sweden) has reported pacu fish in their waters. Many countries in tropical Asia and other continents have pacu aquaculture farms.

Did you know? Tributaries of the Amajari and Catrimani rivers and the Para river in Brazil share the same name Pacu. Nothing connecting the pacu fish with the pacu rivers is known so far.

Survival Mechanism

Pacu fish are highly sensitive to the slightest movements in their surroundings. They immediately hide or swim away to security. Their fastest swimming speed is 10 miles/per hour.

A study on Parana river/small-scaled pacu fish states that they release at least two chemicals when they are injured/identify any danger in the water. One of the chemicals sends a chemical warning/communication to other pacus of the same species (of the potential threat). Thus, they manage to save their community.

Adult pacus prefer flooded waters. They can withstand the force of flowing water while waiting for the fruits and nuts to fall into the water and quickly eat them.

On the other hand, juveniles prefer slow-moving to still waters. They like environments with plantations and rocks to hide from predators.

Physical Appearance

With slight variations according to the type of pacu fish, they share some common traits like

• Flat bodies (plate-like).
• A dorsal and adipose fin (the first and last fin on the upper body respectively,) a pectoral fin (on the body, near the gills), a pelvic and an anal fin (the first and last fin on the lower body), and a tail/caudal fin each.
• The adipose fin is much smaller compared to the dorsal fin.
• The pelvic fin is much smaller compared to the anal fin.
• A serrated line (with crooked edges) runs through the central bodies.
• As discussed earlier, all have teeth that resemble human teeth with a blunt, squarish mouth.
• Their eyes are black with an off-white/red ring around them. They look slightly pronounced (as if protruding).
•  Massive adult size (as adults) depending on the variety (refer to section 1.7), with heavy bodies.
• Lower body portions have darker hues of the same shade as the upper body.
• Their bodies are black, brown, silver, or gray. There are albino pacus (lack color pigmentation due to genetic fault) as well.
• One of the varieties has bright silver upper bodies with a bright red/orangish hue in the underbelly during the juvenile years.
• Long life spans.
• All have similar temperaments, eating, and behavior patterns.

Pacu Fish Life Span

They live up to 15 to 25 years on average. With proper care, they may live for 30 years.

Buttkiss, a pet black pacu in New York City (US), was 43 years old in 2010. It is the longest life span recorded.

Pacu Fish Size and Growth Rate

Their adult size varies between 7 to 42 inches, depending on their type. Thus, there are giant, medium, and relatively small pacus.

Silver My lossoma is the smallest. It can grow 10 inches long. Whereas Black/giant pacu fish is the largest species. Considering their size (even for the smallest), they require 100 to 250 gallons/per fish, making them more suitable for large aquariums or ponds.

A 38 inches long and 17 inches broad/wide giant pacu fish weighing 52 pounds was caught in Florida (US) in 2010.

Another large specimen of the same type was caught in Peru (South America) in 2013. It was 45 inches and weighed a whopping 81 lbs!

Third myth – Many add juvenile pacus to smaller community tanks, assuming it will stunt their growth. While it is true for most other species, pacus outgrow their tank size and keep growing throughout their lives.

Pacu is delicious, can feed many mouths (due to its size), and grows fast, making pacu fish aquaculture commercially lucrative.

Typical Behavior Patterns

• Juvenile pacu fish prefer the company of the same species. Once they grow, they become loners.
• Despite their size and weight, they are very active.
• Mostly swim in the mid-levels in the aquariums, where they find more free space.
• They love to hide behind the tank decorations playfully.
• They can recognize their owners and the people who feed them.
• Their interactive behavior is endearing. They jump to grab their food, appreciating a loving pat.
• They develop their individual personalities with what they like and dislike. This can vary, just like human kids.
• They generally swim in circles as if tagging each other.
• Choosing apt tank mates or having a dedicated pacu fish aquarium is better, considering they can eat anything, anytime, randomly.
• They can hurt other small fish(es) unintentionally while swimming. Avoid housing smaller fishes in the same tank.
• While they are mainly herbivorous in the wild, they accept non-vegetarian fish diets in captivity.
• They will eat live plants and algae from the fish tank.
• Their tanks need tighter lids. The sheer force of their jump can easily displace the tank lid, and they might escape from the tank.
• They react to the slightest disturbance in the surroundings. This behavior can damage/break the aquarium glass walls (due to the force they exert). Keep the aquarium in a peaceful place.

Sexing

The adipose fin (the last, small fin on the upper body) of a male pacu fish has a pointy, sharp edge (like a small triangle). It is curvy in the female pacus.

Male pacus have darker bodies than their female counterparts. Besides, female pacus are large compared to male pacus.

Availability and Price

They are saleable from the time they grow two inches in size. Most local pet stores offer pacu fish for sale. You can purchase them online.

Owning a pacu fish is illegal in a few countries (including a few states in the US). Despite regulations, pacus are freely available for sale. Sellers are sometimes unaware of the legal ban, while a few sell it to unsuspecting customers.

Confirm if it is legal to own a pacu fish in your state/country. Their price starts from $12 onwards and varies according to the variety, size, quality, availability, and offers. 

Types of Pacu Fish

Pacu fish includes the following eight species. All originate from South America.

Colossoma Macropomum (Black Pacu/Giant Pacu Fish/Black-finned Pacu)

It is also known as Tambaqui, Gamitana, and Cachama. True to its name, it can grow up to 3.6 feet long and weigh up to 97 pounds. Their upper bodies are gray, olive, or yellowish. Lower bodies are mainly black.

Those originating from white waters have light-colored bodies compared to the ones from blackwaters. Their life span can be 40+ and even reach 65 years. They migrate to white waters to breed during flooding season.

Metynnis Luna

There are 15 subspecies, including a few silver dollars. They grow 3 to 7 inches long and prefer to live in both slow and rapid water currents.

Mylesinus Schomburgki / Myloplus

There are three different subspecies under Mylesinus Schomburgki. Thriving in rapid waters, adult fishes have double-lobed anal fins. They can grow up to 1.15 feet long. Myloplus has 15 subspecies. They live in both fast and slow-moving water currents. With an average size of 1.8 feet, they have double-lobed anal fins.

Mylossoma/Myletes Albiscopus

It has five subspecies. Their average size is 11.2 inches, with a weight of 2.2 pounds. Silver Mylossoma (Mylossoma Duriventre) is the smallest pacu fish subspecies with a size of 10 inches.

Ossubtus/Ossubtus Xinguense/Parrot Pacu/Eaglebeak Pacu

They are endangered species with egg-shaped bodies. Their upper bodies have a broad arch, but the lower body line is relatively flat. They thrive in fast-moving steep waters.

As juveniles grow, their mouths turn inwards, resembling beaks, explaining their name. They grow up to 10 inches long. Thus, they qualify as one of the smallest pacu fish species.

Piaractus/Myletes Brachypomus

It has three subspecies, including two of the most popular pacu subspecies viz:

1. Piaractus Brachypomus/Red Belly Pacu/Pirapitinga.

They have shining silver/grayish silver upper bodies with a red to orange tinge in the lower belly, giving them an enticing look. As they mature, the red hue disappears.

Juvenile red-bellied pacus resemble red belly piranhas. Predators keep away from them, mistaking them to be piranhas. Quite a natural trickery!

They grow 2.9 feet long and can weigh up to 55 pounds.

• Piaractus Mesopotamicus/Small-scaled Pacu/Parana River Pacu.

Small-scaled pacus have tinier scales compared to other variants. They have silver/gray upper bodies with a golden to yellowish hue in the lower bodies, from the mouths to the start of the anal fins. With an average size of 2.03 feet, they can weigh up to 44 pounds. They can survive in cold waters of 15 degrees C (refer to section 1.2 for details).

Tometes/Tometes Trilobatus

It has seven subspecies. Their incisor teeth are thicker and lower than other pacu variants. Plus, they are not well-rooted in the jaw, restricting their utility to cutting leaves.

Their silverish-gray bodies have a lighter shade in the lower half. Male species have an extra anal fin lobe, longer dorsal fin, or red pattern on their bodies (unlike other variants).

Utiaritichthys/Utiaritichthys Sennaebragai

Its classification genus is still unclear. It has three subspecies. With an average size of 1.06 feet, they live in fast-moving waters.

What do Pacu Fish Eat

We already know their diet in the wild (refer to sections 1.2 and 1.3).

Pacus need a lot of food to manage their ever-growing bodies. Hence, they are not likely to refuse food (unless the water temperature reaches 18 degrees C).

Their diet in captivity can include the following:

• Fresh and boiled vegetables – Zucchini, Carrots, Lettuce, Potatoes, Peas, Spinach, Broccoli, Sweet Potatoes, etc.
• Fruits – Bananas, Grapes, Apples, Papaya, etc.
• Ready-to-eat foods like – Herbivorous Pellets, Algae Wafers, Herbivorous Gel Diet, Spirulina Flakes, etc.
• Non-vegetarian food – Fish Pellets, Insects, Crustaceans, Snails, Shrimp, Squids, Earthworms, etc. These should not be served regularly.
• Some pacu fish accept live goldfish too. However, there is a potential risk of infection, as goldfish are prone to diseases. Please use your discretion.
• They eat rotten/decaying (not infected) food without fuss.

Feed them once a day. The size of the morsels should be easy for them to eat and bite (they do not chew). Avoid over-feeding, as uneaten food will contaminate the tank water within a few hours.

There might be slight differences in what your favorite pacu fish enjoys eating. Include what they love in rotation with other veggies and fruits based diets for complete nutrition.

Breeding Pacu Fish

Most pacu species breed during the flooding season in their respective regions. Due to geographical differences, these months/periods vary, but the behavior is almost similar.

Pacus mature sexually from 3+ years of age. There could be slight differences among different species and within the same species due to genetic factors.

They migrate in groups for spawning, but their breeding grounds are unknown. Spawning is when a female fish releases eggs into the water/on any underwater surface. Simultaneously, the male fish releases semen to fertilize the eggs.

Breeding in the Wild

When the water level reduces, mature pacus migrate in groups/schools to floodplains. At the onset of flooding season (which assures availability of ample food/vegetation), they release their eggs on rocks/other surfaces in clear waters near the banks.

A female pacu releases approximately 150000 to 200000 eggs per spawn. Thus, millions of eggs are released and fertilized overall.

The activity continues during their spawning period (which could be a few months), after which adult pacus return to the flooded forests.

Nature separates Pacu fish parents after spawning, so they do not feast on their own eggs/frys.

Many eggs do not fertilize or fall prey to larger fishes. Few that hatch do not survive till adulthood due to threats from predators, infections (if any), or water currents swaying them away. Survival of the fittest is the ground rule.

Challenges in Captive Breeding

A single mature pacu fish requires a tank size of 150 to 200 gallons due to its size. Most owners cannot own more than one due to space constraints.

Even if they manage a pair, the adult pacus do not spawn in aquariums. It could be due to their migratory instincts.

Caring for 2 lakh eggs and the surviving pacu fry(s) till adulthood can be a task in aquariums. Also, you would need a separate tank(s) to house the fast-growing juveniles, assuming (randomly) even 10 out of 2 lakhs survive.

There has been no natural pacu fish breeding in aquariums. Commercial breeders and aquaculture farms breed them in large ponds/aquariums using hormonal injections.

Artificial Spawning

Breeders nurture good quality mature pacu broods in ponds/large aquariums with regulated water parameters. A protein-rich diet ensures healthy parents, resulting in healthy offspring.

• They stop feeding the breeding pair 48 hours before the artificial spawning.
• Hormonal injections of the pituitary extract are available in aquatic research facilities.
• Injections are given to the breeding pair as follows:

Female pacu fish:

1. 1st injection (0.50 teaspoon/per 2.2 pounds of her weight).
2. 2nd injection (2.5 teaspoons/per 2.2 pounds of her weight) after five hours from the 1st injection.

Male pacu fish:

One injection (0.5 teaspoon/per 2.2 pounds of his weight) simultaneously with the second dose to female fish.

• The eggs inside the pregnant (gravid) female pacu fish become visible approximately six hours after the second dose.
• Her eggs are extracted manually using a syringe and kept in a tray with dechlorinated water (one-third the weight of eggs).
• Freshly extracted male pacu fish sperm (10 drops/per 150 cc of eggs) and the eggs in the tray are allowed to interact by shaking the tray for 15-20 seconds after adding some water.
• The eggs are placed in glass jars with some matured aquarium water. They fertilize in 48 hours.
• After 2-3 days of fertilization, freshly hatched fry(s) separate from the shells and swim free.

4.3.1 How to Feed Pacu Fry(s)

• They are given baby fish fry food (like cultured infusoria and green water) six times a day, in tiny proportions.
• Fish fry foods are available in an aquatic research facility. But they can also be prepared in-house (in advance) to reduce costs.
• After ten days, the baby pacu fish are moved into grow-out tanks and given fish food (after powdering) thrice a day in small quantities befitting their tiny mouths.
• Gradually, their diet is almost the same as adult pacus, except for the quantity and morsel sizes.
• Once the fry(s) are large enough to defend themselves, they can be kept in the pond/large aquariums with other adult fish.

Tank and Water Parameters

Tank Specifications Overview (Pacu Fish)
Minimum Tank Size	200 Gallons or more
Water Temperature	76.0 to 82.0 degrees F/24.5 to 28.0 degrees C
PH Level	6.0 to 8.0
Water Hardness	2 to 15 dGH

Tank Size and Setup

As discussed earlier, you will need a large tank size for pacu fish. Calculate 10 liters of water/per inch of fish. If you start with a smaller tank, you will need to change to larger tank(s) frequently, considering their fast growth rate.

Juvenile pacus enjoy the company of the same species. Consider adding more than one, if possible.

Sterilize everything that enters the tank. All decors should have rounded edges and smooth surface(s).

Place each decor firmly with good support. Once the pacu fish grows, its simple movements may misplace/damage the decorations.

Add artificial plants (along the corners/walls) to replicate their natural habitat. They like to hide in plants. Avoid live plants, as pacu fish will eat them up. Adding rocks and driftwood also helps, as they will provide hiding space and will not displace easily.

Add minimum decor aesthetically to provide maximum free space. Also, consider other tank mates (if any) and their space requirements.

A substrate of small rounded stones of contrasting colors is an excellent choice.

Use an adjustable light with dimmers for subtle lighting. Switch off the aquarium lights at night.

Oxygen and Filtration

A huge appetite due to a large body causes huge waste/bioloads in pacu fish tanks. You need an effective filtration system to clean the water ongoingly. Besides, the filtration must be apt for the tank size.

It is advisable to use more than one filter to clean distant corners. Do not change/clean the filter cartridges of all filters simultaneously. It will disturb the aquarium ecosystem.

Pacu fish need well-oxygenated water. Keep the water current slow-moving when pacu fish is young, and increase the water current slightly (not very fast), once they grow.

You will need a heater and thermometer for the aquarium to keep the water warm.

Ensure no wires from the filter, oxygen pump, lighting, etc., are hanging or loose. They might break accidentally by pacu fish’s movements, causing an emergency.

Perform 10 to 15 percent water changes every week and remove any excess waste not cleared by the filtration system.

Tankmates for Pacu Fish

Ideal pacu tank mates should have the same non-aggressive temperament and large size to avoid falling prey to or feasting on your pet pacu. Besides, they should be able to stand for themselves and not be timid, as pacus may occasionally nip the fins of tank mates.

Oscars, Arowana, Datnoids, Green Terror, Sailfin Plecos, etc. make good tankmates. Alternatively, have a dedicated pacu fish aquarium.

Interesting Facts and Controversies about Pacu Fish

• Pacu fish has been mentioned in the book “Through the Brazilian Wilderness,” written by Mr. Theodore Roosevelt, the 26th US President. One of his team members caught two pacus. Mr. President states that they were delicious to eat!

• A leading newspaper in Seattle (US) published a story on a pet pacu fish named Swish. He lived in the aquarium of a popular restaurant for almost 20 years.

His interactive personality struck a chord with everyone. He would happily come to the front aquarium window, munching carrots. Aquarium service technicians would scratch his head during tank maintenance, and he would rub his body against their hands in a loving gesture.

Swish had stayed with two different hotel businesses earlier and was popular there too. The new owner chose to care for him rather than feed him to the customers.

He was 30 inches long, 31 years old, and weighed 32 pounds when he died in 2016. A pet pacu can give you an affectionate bond for years.

• A leading newspaper in Arizona (US) reported about a fish with human-like teeth caught by a fisherman in 2018. The Arizona Game and Fish Department identified it as a pacu fish. The report highlighted concerns about illegal pacu trade, fish owners dumping overgrown home aquarium pacu fish into the wild, etc. Pacu fish were a threat to the environment, according to this report.

• It is not legal to keep a pet pacu fish in California (US). In Arizona (US), you need a permit to own one.

• Several reports from 1999 to 2001 in Papua New Guinea led to the pacu fish gaining a notorious reputation as an invasive species.

Due to scarce fruits, nuts, and seeds, the non-native pacu species ate local fishes and floating vegetation destroying natural fishing nurseries and local fish species. They also reproduced in large numbers, pausing an environmental threat.

There were two incidents of pacus biting the genitals of local men in 2001.

• Intrigued by this media story, Jeremy Wade (Animal Planet star and host of the River Monsters series) personally went to Papua New Guinea in 2011. He caught a few pacu fish that he set free in the wild afterward. In one of his interviews, he tried to explain things logically. He was not attacked by pacu fish while fishing for them.

• In another incident, a pacu fish bit the finger of a small girl at the Edinburgh Butterfly and Insect World in Scotland. She was wiggling her fingers at the pacu fish when this happened.

• In 2013, a headline in Denmark by Professor Moller warned Danish men against the danger of testicle-biting fish caught in Denmark.

However, in an interview with CNN, he clarified that the headline he wrote was a joke. But people took it otherwise.

Many native people from South America confirmed that they have been catching pacu fish for years without any eventuality.

Evidently, isolated incidents and wrong headlines were overblown by the media for publicity, creating a lot of misconceptions about pacu fish.

We exploit aquatic life, introduce them to newer environments, trade in them illegally, and deal with them irresponsibly. How can we blame them for their responses, which are pure survival instincts? Who is invasive? We or the pacus?

Fourth Myth. Pacu fish are aggressive. No, but they will react if provoked.

Final Thoughts

Indisputably, pacu fish is amazingly alluring with individual personas. These gentle giants have a charm that is difficult to miss. Apart from that, they unknowingly contribute to aquatic ecology by promoting the growth of underwater plantations in different locations by releasing their bioload (waste) containing seeds.

No wonder fish lovers cannot resist the urge to own them.

Decide if you will care for a pet pacu for almost 15+ years. Make an informed choice before adding an exotic pacu fish to your collection.

 Contact local pet stores and aquariums if you need to get rid of an overgrown pet pacu fish. They accept fish-back donations. Releasing pacus in foreign waters in the wild can be fatal for them if the water gets cold. It is not uncommon to eat a pet pacu fish in some regions.

Let us create a win-win situation for aquatic life every time we own/interact with them.

Hopefully, you are a pacu expert now. We wish you a happy pacu parenting time!