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This page will give a completely detailed profile of the selected fish, from A to Z. The profiled fish will be chosen randomly by Badman, and will come from the complete genre of tropical fish. New profiles are added on a regular basis. If you would like to submit a profile for the site please contact me. Don't forget to let us know you experiences with this fish by filling out the

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

South America


Colossoma macropomum

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, thatís 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

Colossoma macropomum

Colossoma macropomum

Common name:

    Black-finned Pacu , Pacu and Tambaqui

Image gallery:

    Additional species photographs


    Badmans' Forum


    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


    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.


    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.

    Colossoma macropomum


    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

Your comments:


Please remember that the following comments are personal experiences and may or may not apply to your setup. Use them as guide to help better understand your fish, like us all individuals will behave differently under different circumstances.


From: Dax Druckman
I just bought my 2 pacus about a week ago now. I had pacus when I was younger and I really liked them a lot. I got out of having an aquarium back then and now I am interested again in having fish. I chose the pacu fish for my new aquarium. I understand that they will get really big, but I am ready for them. Pacus are great fish and they are intelligent fish. Pacus are not for beginners and they require knowledge of this species. I remember Pacus getting really big and they are a nervous fish when you move quick around the tank. My new Pacus are doing very well and are growing really fast. I bought them at the size of quarters. Now they are the size of silver dollars (NOT THE FISH, THE COIN). So, people interested in Pacus must understand that these fish get big and require a really healthy diet. Some vegetables and fruit are required for a healthy diet. Pacus are gentle fish, but they can nip other fish and you. Pacus are great, but do some research first before buying this fish.
From: Angela
I bought 2 pacus at Walmart labeled as 14 years ago. After 5 years one ate the other one and now I have one left and have had to upgrade tanks many times throughout the years. At this point I either have to surrender her to a zoo that will take her or build a specially made tank for her. Since I have fallen in love with this little monster I will have to build a tank. I love my monster, but I wish I would have been informed of the growth of these fish before I bought one. I bought her when I was in high school and I have learned my lesson, I will never buy another pet without doing my own research. Pacus should not be sold at regular pet stores because the fish will end up suffering in the long run if the owner is not able to keep up with the constant demand for a larger tank.
From: Amy
I have 2 red bellied pacu's, Right now they are no bigger than a saucer. I currently have them in a 200 gallon tank with 1 common Pleco Tank looks empty but I know before long they will fill it out. They don't seem to be really big eaters, always on the bottom of the tank, I have fed them flakes, lettuce and carrot's and they really love algae wafers. I love watching them, they really have a personality
From: Kris Williams
Having always wanted a large fish, three and a half years ago I bought a baby Pacu. "Carl" as he was soon named was tiny at the time, no bigger than a nickel. Well, three and a half years later, he is easily 13 inches long. I feed him a floating large cichlid sticks, as well as a variety of just about anything else vegetable wise. Even large chunks of banana disappear right down him with no problem at this stage.
Make no mistake, this has got to be the fastest growing fish I have ever raised. While he started out in my 29 gallon community tank when he was a baby to avoid my larger more aggressive fish, I always knew he would move up through the various sized tanks I had throughout the house. By the time he was 4 months, he was nearly 5 inches long, and into my 55 gallon South American biotope tank. Not much longer, and he inherited my 100 gallon, so forth and so on.
As far as personality goes, he really is my favorite fish. If I'm within eyesight of the tank, "Carl" watches the "Food Bringer" (me) with great interest. When he was smaller, only 6 inches, he did bite me once in the arm as I cleaned the tank. Keeping in mind that they are relatives of the piranha, and that they DO have teeth, he actually hurt me a bit. I'm glad to report that only happened once, and now he'll let me stroke his sides when I clean the tank. I'm sure he had just felt cornered or scared at the time of the incident, being a little sketchy as they are. However, he never has hurt another fish, and to this day, he resides with my 4 inch long female Frontosa who, sadly, I had to evacuate from another tank due to an overly zealous male. "Carl" doesn't mind her company in the least.
I will say that I have only ever kept this fish in acrylic tanks. Seeing his occasional panic attacks (far less frequent as he grew older) there is no doubt in my mind he could have easily destroyed a glass tank. A vision, at the very least, of a glass tank's top being hurled to the floor would have definitely occurred during some of his more spectacular tirades.
All in all, as I said, he is my favorite fish, and I am glad to know that he will be with me for a decade or more. If you're not committed to giving them the space, though, don't buy one. Remember, that dime sized silver little fish is going to be a large black monster within a few years.
From: Diane
I have just bought my first pacu. I got it at Walmart, but I was smart...I seen the fish and was interested in it so I went home and did some research, BEFORE BUYING THE FISH !!! As a pet owner it is OUR responsibility to find out about the fish/ pet BEFORE buying it !! I knew how large he would get,what size tank he needed etc. before I brought him home. Needless to say, I love him !! He's still small, only maybe 2 inches or so. I've had him only a few weeks but he's growing everyday. I can see how much he's grown already. He loves little pieces of grapes, apples, flakes, and shrimp pellets etc. He's not very keen on algae tablets Anyways, just remember it's OUR responsibility to research and ask questions BEFORE getting fish or any other little critter...they don't want to be pawned off or dropped in a lake somewhere when their owners decide their "too big" ! Stop blaming pet stores and be responsible pet owners !
From: Bill (UK)
About 4 years ago, a bucket appeared at my house with (apparently) an unwanted 8-inch piranha in it. I had a 5-foot long tank spare so he came to live with me, great happy fish for a while, just fed him fish and meat, seemed happy, Iíd never heard of a pacu at that stage. Iíd noticed a few things about him that werenít quite right, didnít have the protruding jaw, his teeth were short and stumpy instead of sharp and serrated, his eyes sat slightly lower in his head and heíd lost the red belly, but Iíd been told it was a piranha and so accepted it. I excused these things, thought heíd get the jaw and teeth with age, and I know female red bellied piranhas lose the red colour when breeding. It was only after almost a year later, when he found it difficult to turn round in the 12-inch wide tank. I know piranhas grow approximately 10 inches; heíd got to be 11. I started looking for a new big tank, luckily I found one on ebay so big, nobody else would want it, and at very low cost, I only just got it in my house. Being a corner tank (approx. 150g), the shape makes it much more roomier for him than an elongated one, he loved it and perked right up. A year later with people always remarking on how he was growing, but seeing him constantly I couldnít tell. On measuring him 16 inch now, started researching what in fact he was with no clues. Personally I was pleased to find out what he is, just wish Iíd known from the start. He is now 20 inches long, a foot high and 3 inches thick, shares the tank (believe it or not) with a school of 30 x 1 inch long neon tetras (he doesnít bother them at all, itís amusing watching them going around the opposite sides like 2 magnetic +ís, and they eat all of his crumbs, keeping tank clean). Heíll eat virtually anything, but has his likes/dislikes as anyone does. I buy no special food for him; he has what I have (except fats and sugars etc.), all fruits, vegetables, meat, fish, nuts, cooked or uncooked. Heís like a puppy Ė bright, cheerful and playful, loves attention and gets very excited (to the point youíve got to leave him alone to calm down). You cannot have many decorations or ornaments with these fish, for obvious reasons, I just have a huge realistic looking plastic plant in the middle floating to the top rooted down with fishing line, not unlike kelp, and be careful with things sticking out or floating from pumps, filters, heaters etc. they chew anything and with a mouth like pair of nut crackers, if you prefer to keep your fingers, take heed, as a friend found out the hard way a few months ago, despite the warning, what a mess, itís almost healed now though, and with a few more months of psychologist counseling the nightmares will ease and sheíll lead a normal life again. Seriously though, Iíve kept so many fish through my life and Iíd safely say the pacu is so different to anything Iíve had before, such a pleasure and easy to keep, heís called Little Bigman, and he seems to recognize my voice. He could potentially double his size and live another 20 years, if he needs more space sometime, Iíll cross that bridge at the time, but Iím very attached to him. Iíve been in a wheelchair some years now and heís great company when Iím at home.
From: Lilly
I was reading through the comments to the pacu profile and noticed that several people commented about the lack of information LFS gave them about how big pacus get, and how the store's total length description of the fish are inaccurate. I use to work at petsmart. I was aware of the size that pacus got. I asked my manager if we could change the tag to the correct total length. She told me we couldn't because all the stores have to say the same thing on their tags. She wasn't willing to call cooperate to ask them to change the length of the pacu to the correct size. We had the same problem with other large growing fish. Like the clownfish and the iridescent catfish. I asked my more fish-savvy co-workers about what they tell people about the pacu and what to do in my situation. They nodded their heads in agreement that description for the length of the fish was incorrect and not good for people who didn't know better but they couldn't do anything about it either since my manager wasn't willing to. They told me that they would just tell customers that the pacu grows several feet long and should only be houses in the largest tank the buyer can afford. So this is what I began to tell customers also. Fortunately, I didn't get many people interested in buying the pacus at our store because people thought they were piranhas. When people did for me to bag this fish up for them I found that most of them either didn't believe the fish really got that big, or didn't care that they got that big because they believed in the "fish only grow to the size of their tank" myth. When I tried debunking that myth they became agitated and still wanted the fish anyway. It was that store's policy the ask every customer what size tank their fish were going to be put in and what fish were already in there. Since the first question I always ask a customer who wants a fish is about the size of their tank, I always knew if the fish was compatible for them or not. Ironically, none of the people that approached me for that fish had a large enough tank. Our store also could refuse the sell a fish if they knew it would be kept in inhumane conditions. I had to turn those people that couldn't accommodate the fish away. We did the same thing for small animals. I've heard at other petsmarts they don't do this. I was glad I was working in a store that could at least could do that much for the pets they sold. Even if it was "just a fish". For those of you consumers out there I encourage you to write to petsmart, and other pet stores. Ask them to change the description to the correct information. Customers have more power over the situation than the people working at the store do.

Badmans Note: Lilly and all interested parties you will be happy to know this effort is well underway, please visit the No clowns in a cube website for ways YOU can help the effort.






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