This profile was written by Debbs, a regular on the sites Forum, check it out if you have a questions or comments.






Colossoma macropomum



    Often sold as juveniles and mistaken for the Piranha, the Pacu soon outgrows all but the largest aquariums. If you are willing to meet its space requirements its’ personality and ease of care will offer many years of enjoyment. These are pictures of Debbs Pacu at 17″


Quick stats:

Listed tank sizes are the minimum
Size: 3 feet, that’s right 3′ !! (92cm)
Tank: 75gallon + when small
Strata: Bottom, middle
PH: 6.5 to 7.0
Hardness: Soft to medium. dH range: to 20.0
Temperature: 72°F to 82°F (23-28°C)


Order: Characiformes
Family: Characidae
Subfamily: Serrasalminae
Genera: Colossoma
Species: macropomum



Common name:


Black-finned Pacu 

    , Pacu and Tambaqui


    Brazil, South America

General Body Form:Similar in shape to the piranha and part of the source of the confusion the pacu is a tall, laterally compressed fish with large eyes and a slightly arched back


Coloration: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.

Maintenance:Recommended Aquarium size – They grow fast so my recommendation would be to start out in a 75+ to 300 gallon. If you start out in a smaller tank you will be upgrading every few months.

Water – do best in softer, slightly acidic water. Between 6.5-7 is good.

Temp.- 78-82 degrees Fahrenheit (23-28°C)

Diet – Pacu’s are reported to be herbivores but are in fact omnivorous (eats anything).
Sinking food pellets such as HBH’s Super Cichlid Sinkers or Spirulina Pellets are very good foods to keep a healthy Pacu. They need a balanced diet so giving them veggies such as romaine lettuce, peas, carrots, celery, zucchini and fruit such as nectarines, apples, grapes are recommended in their diet. Algae wafers are a favorite also.

Life Span– This fish lives for twenty + years, depending on species and care given.

In the wild, they interact and play with each other, indicating they are indeed a schooling fish. However, as they mature, many varieties of Pacu become more solitary and no longer need same-species companionship. Pacu can, like most fish, be kept with fish with similar care requirements and temperament. This generally means fish that are going to get large and that are neither too aggressive nor too timid, as the Pacu will occasionally nip fins.

Personality of a Pacu – I can only speak from my experience with our Pacu over the last 2yrs.
This Pacu is a what I’d call a “;Gentle Giant”. He is in a 180 Gallon tank with a variety of Cichlids. He’s the least aggressive of them all. Yet he won’t be bullied by any fish. When a cichlid tries to nip him (from the back end ) I’ve seen the Pacu turn around and chase the fish away. He sometimes seems to make a game of this, it’s very hard to explain but I’ve seen him chasing a fish in circles but only to end up turning his back on the fish and waiting to be nipped at again. Here is another example of his personality. When I clean his tank, he loves me to rub his sides as he swims around my hand over and over again. He has personality, likes and dislikes and shows his vulnerable dependency upon us for companionship, food and care.

He is as most Pacu’s are known for, skittish. Any fast movement or vibration will cause a panic like reaction from the Pacu, sometimes resulting into banging into the glass, heater or decor. Pacu’s are known also as “tank busters”. I can relate to that, and even though my Pacu hasn’t busted a tank yet, I know with his massive strength, bulk, and panic attacks he can easily break glass.

My Pacu is 17″ and I believe almost 3yrs. old. When we first received this fish from a friend at approx. 7″, he was mistakenly Id’d as a Pirana. He sure looked like one!

At a young age, Pacu’s look almost identical to their cousin, the Piranha. The easiest way to tell the difference is that a piranha’s lower jaw will jut out much more then that of a pacu’s. As the Pacu grows, the differences will become much more obvious. He will become deep bellied and wider.

Lastly I’d like to warn people, hobbyist, fishkeepers. Do NOT buy this fish if you are not planning on keeping him full term. He will require a 300 gallon tank within a few years. This is a fish that is easy to keep in the right conditions, BUT, he also is a fish that needs room to grow, and grow and grow. I’m very upset that this fish is sold to the public without a warning of the max growth size. In one store I had seen them state his max. size to be 12″. I wrote them telling them the stats of this fish and was thrown off by an ignorant reply “we sell according to consumer command.” Well the majority of consumers would not wish to have a fish that grows to 3′ if they knew about it, unless they were heartless people. That’s my reply, and that’s why I’m putting this on this board. If you’ve a heart, you’d not buy this fish unless you plan on a 300+ gallon for him to live a full, healthy life.

I forgot to add that the Pacu’s do and will eat small fish without hesitation. This is a warning, not a recommendation.

I also would like to add that at 17″ long, his height is 11″ and width almost 2″. This is just and example of the impressive girth these fish have. They are now being raised in huge fish farms throughout the world as a food fish.


Biotope:Young stay in Black waters of flood plains until maturity, adults in open water and flooded forests.


Sexing -The male’s red coloration is much brighter than the females, and his dorsal fin comes more to a point.

Little (or nothing) is known of their breeding habits, due to the large size and space requirements


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