Top 10 Fish you should never buy for your Aquarium

Wait a minute, there are fish I shouldn’t buy for my Aquarium? Yes, that is correct. In fact there are lots of fish that nearly every pet store / fish store sells that have no place in any standard home aquarium. Today I’m gonna go over the top 10 fish you should never buy for your Aquarium and why you shouldn’t buy them. If you’ve got a custom tank over 1,000 gallons then this list probably isn’t for you but if you think your 55 gallon tank can hold every fish under the sun, keep reading because it can’t. This isn’t to say you can’t get all of the fish below, you can but be aware that some of them will outgrow you so keep that in mind as you proceed.


Large Pacu pictured above.

10. Common Plecostomus (Hypostomus plecostomus) – Sucker fish, Algae eater, Bottom feeder, Pleco, Common Pleco, etc. It doesn’t matter what you call them, you shouldn’t buy one. The common plecostomus can grow to 2′ long! These poor guys are sold by the thousands at prices around $3. They are usually about 2″ long and sold as “Algae eaters” to keep the tank clean. WRONG! In fact it couldn’t be more wrong. They actually make the tank dirtier, much dirtier. They eat a lot and poop just as much. As for what they eat? Algae is a part of the diet but the tiny amount growing in your tank isn’t anything close to enough food. They should be fed Algae Wafers, Sinking Pellets, and Veggies. (Zucchini, Cucumber, etc) There are hundreds of different Plecostomus species, some of the smaller varieties such as Bristlenose are much more appropriate for Aquariums. They should however be treated like any other fish and fed a proper diet, not just “oh it cleans up after the other fish”. They also need hiding places such as driftwood or caves made from stacking rocks. Some species eat wood and meat based diets as well, so do your proper research.

Common Pleco @ 6-7″

Common Sailfin Pleco @ 6-7″. As you can see they have a very prominent spotted dorsal fin that is rather large, hence the name Sailfin.

9. Goldfish (Carassius auratus auratus) – Yes, you read that right. You should NOT buy Goldfish. They do not make good starter fish, they should not live in bowls, and they get huge. Yes, that tiny little Goldfish can get huge. In fact it can get bigger than the bowl most people keep them in. If you do love Goldfish and want some, that is great but don’t think for one second your 55 gallon tank will make a nice life home for a dozen of them. You need a pond in a perfect world but if you can’t provide that at least get the largest Aquarium you can afford/fit in your space. A lot of people will disagree with me but a 180 gallon tank is the minimum size I will suggest for a Goldfish tank, yes that is a huge tank. Goldfish eat a lot and poop just as much so not only do they take up a lot of space once they grow up, they also produce a lot of waste. So a large tank is required unless you want to do water changes every day and watch your Goldies swim in circles. If you can provide a large tank, by all means go Goldfish crazy. If you can’t do that then you should probably never buy a Goldfish. This includes some of the fancy variety of Goldfish as well, I’ve seen photos of Monster ones. I do not know if all the fancy varieties get huge though, if there are some that stay small let me know in the comments and I’ll add a note here.


Here is a Goldfish that was able to grow up in a lake instead of being confined in a tank. Try stuffing that into a fish bowl..

8. Iridescent Shark (Pangasianodon hypophthalmus) & Paroon Shark (Pangasius sanitwongsei) – Both of these Monster Catfish are regularly for sale at big box and smaller pet stores (The Paroon is not seen as often anymore), which is ridiculous because neither belongs in an Aquarium. They both come from rivers in Asia such as the Mekong where they can grow into true giants. The Iridescent can reach 4′ and nearly 100lbs, where as the larger Paroon can reach 8′ long and 600lbs! They are both very active swimmers and require plenty of room to roam, so unless you have an Olympic sized swimming pool to spare don’t bother with either of these monsters.

Huge Iridescent Shark in a massive Aquarium (Image property of Melanochromis on Wiki)

Giant Paroon Shark and this one isn’t even full grown. They are also known as the Chao Phraya giant catfish.  (Image property of

7. White tip Shark Catfish / Silver Tipped Shark / Colombian Shark Catfish (Ariopsis seemanni /Hexanematichthys seemanni)– These guys are just as cool as they come. They look like little sharks, sort of. They don’t even get that big. Topping out at only about 14″ long, so a huge aquarium isn’t even needed. The reason you should never buy this fish is because it’s not a freshwater fish. They can live in freshwater for short periods growing up but if you want to keep your fish for years you’ll need a brackish water tank and eventually a full saltwater tank. So you can’t really keep anything with them except fish that can tolerate such a change, which is very few. It is also a good bit of work to continuously raise the salinity and you must take measurements and continuously monitor water conditions. So this is why we don’t suggest these guys. If you can provide a good sized aquarium and are willing to do all that work, then by all means go for it. For those who can’t, it’s best if stay away from these guys. Try some Corydoras catfish instead.

Juvenile Colombian Shark Catfish.

6. Silver Arowana (Osteoglossum bicirrhosum/ Black Arowana (Osteoglossum ferreirai) – This also includes Asian Arowana, Australian Arowana, and African Arowana. However we are focusing on the Silver as it is by far the most common here. The Silver can reach 4′ long and is a very active swimmer, you really need a pond or huge custom tank to provide a true for life home for a Silver Arowana. Many people keep them in 180 gallon tanks or even 450 gallon but as large as those tanks are, the Arowana needs more space to truly have room to swim. They are powerful jumpers too, many people have lost them due to the fish jumping out. They can blast right through a lid when large. You must put rocks on them to hold them down, trust me. This or have a proper large pond (with netting or a border) where it doesn’t matter, even a 300 gallon Rubbermaid beats most tanks. It’s all about the surface area where the Arowana swims. The 300 gallon Rubbermaid Tub has a 69″ x 63″ measurement at the top edges, that is about 5′ x 5.5′ internal dimensions which equals a lot of surface swimming space. If you’ve got a normal tank, NEVER get one. It will outgrow it in super short order. Wait until you have a life home or at least the Rubbermaid tub mentioned above. They are only a couple hundred bucks, plus Arowana look best from the top anyway.

Baby Silver Arowana 6-8″

Monster Silver Arowana

5. Red Belly Pacu (Colossoma brachypomum) / Black Pacu (Colossoma macropomum) – These poor guys are sold at most stores for just a few dollars. The buyers are told a 55 gallon tank will suit them fine and they buy a few, you know so they have friends. UGH! The Pacu species all get huge. We’re talking the size of a garbage can lid here, you need a truly massive home for these guys. If you can buy the tank at a pet store, it’s too small. Custom monster tanks only apply. Oh and they are strong, if you do try to keep them in a small tank they’ll just break the glass eventually. It can happen.

Huge Pacu, just compare it to those adult Oscars. (Image property of

4. Arapaima Gigas (Arapaima Gigas / Arapaima Arapaima) – Also known as Pirarucu and Paiche. The Arapaima is in contention for the longest fish in the world. Is that enough to convince you that you should never get one? 12′ long and hundreds of pounds. If you could fill your entire house with water it might be big enough to hold an Arapaima. Just forget it unless you’re one of those select few people crazy enough to build a home sized aquarium. This Monster of the Amazon is a food source in South America and the population is actually being depleted yet they still pop up for sale from time to time.

Look at the size of that Arapaima Gigas compared to those adult Oscars. Note the massive Pacu sitting below the Gigas, they too are absolute monsters. The size of garbage can lids and thicker than a phone book.

3. Bumblebee Grouper / Atlantic Goliath Grouper / Giant Grouper (Epinephelus itajara / Epinephelus lanceolatus) – Oh where do we begin with these guys. From the people who claim they have converted them to fresh water to the ones who only feed them sparingly to slow the growth. I’ve heard it all. The point is, it’s a Saltwater fish and it’s a monstrous one at that. At an adult size of well over 6′ and 500lbs I wish anyone good luck housing that thing. Oh and if they wanted to be in freshwater they’d swim up a river and migrate into it permanently. Guess what? They don’t. It’s a saltwater fish, I don’t care who told you otherwise or how long one has survived in freshwater.  There are plenty of smaller super cool Groupers available, get one of those and skip the these. (Here is a video of one stealing a fish from a diver under water)

2. Alligator Gar – (Atractosteus spatula) – I really should not even mention these. It should be obvious. Yet people still get them, it is rather amazing. There are dozens of photos of 6’+ examples floating around. They are on River Monsters and numerous other shows. You don’t need one. Stick with a smaller gar species, and even then you need a very large tank.

I am not even going to post an image, surely you’ve seen one of these. Just click here for the Google image gallery if you haven’t seen these swimming torpedoes with teeth.

1. Redtail Catfish (Phractocephalus hemioliopterus) / Tiger Shovelnose Catfish (Phseudoplatystoma Faciatium) – I’d say easily the most popular Monster fish for Aquariums. These guys both get huge, over 4′ and 100lbs. The Hybrids also get just as large, often called RTC/TSN Hybrid. Make no mistake, the hybrids are all man made not wild caught. There are numerous Tiger Shovelnose species that have varying patterns. Some of those  may be called Hybrids by mistake. Unless you’ve got a pond leave these guys alone, try a smaller species. There are plenty of them such as Raphael catfish and Pictus Catfish.

Need I say more? The Tiger Shovelnose gets just as large. Note the giant Pacu in the back corner.

Honorable MentionsOscars, Goonch Catfish, Mantis Shrimp, Fire Eel, Large Bichir species, Peacock Bass, Saltwater Sharks, Stingrays, Bass, Eels, and Koi.  (these are all for varying reasons)

Check out some of our other fish lists.

*- some need very large tanks


    • Mihajlo says:

      Goldfish in a 180 gallon? I find that ridiculous. I’d say the minimum for even one adult common goldfish should be 90 gallons (Half!) Since common goldfish really only average out at 15″ adult and take forever to grow to that size even in the wild (a few years ATLEAST even with sufficient food in the wild). And before you start accusing me of keeping goldfish in bowls I keep them outside in a circular pond 2ft deep and 7ft wide and I have 4 young wild caught ones. But it definitely deserves to be on this list because it’s without a shadow of doubt the MOST neglected fish EVER. And then again there are fish that really don’t deserve to be on this list like the bumblebee grouper or the aropaima. How often do you see those and it’s really common sense. But I see WAAAY too many baby iridecent sharks and pacus in LFS sadly…. And for stingrays there is a variant that only gets 12-14″ (reticulated stingray) in diameter and a peacock bass that only maxes out at 18″ (kelberi peacock bass), But then again they should only be kept by the most EXPERIENCED KEEPERS with atleast a 180 gallon tank.

  • Curtis says:

    I wouldn’t put Goldfish or pleco in the top 10. There are far more other fish that grow to big for the biggest aquariums.

  • Timbra says:

    But pleco and goldfish are the most common to be abused. I’d add Oscar to that list.

  • Kyle Carter says:

    I have 6 out of the 10. In all honesty. Yes these fish are hard to keep and require a lot. Mainly space. And a good diet. But if you have the space and time. Nothing wrong with them. Red tails and tigers grow to tank size. Without affecting them. Plecos are great for ponds. Plenty of algae. Or an outdoor aquarium. Goldfish just take way too long to get big. And if goldfish are in there. Then so should koi. They grow faster and get bigger. Tons of other fish that shouldn’t be in aquariums for better reasons than size. As that’s what all those have in common. I’d say number one should be aropima. Way to large and aggressive. Not to mention the bone of a head and jumping and breaking glass or acrylic and potentially I hiring them by not having space.

  • Carrie says:

    Thanx for all the information. A bit too late for me to find the article, sadly. We recently started a tank and went through alot of trouble and money just because the pet stores fail to inform us properly. We lost almost all of our fish too from their contaminated water. And I already had healthy fish from before…lost those as well. I’m glad to hear of the advice about planktons. I really really wanted one, but now..I will find something else : ) Thanx again!

  • david says:

    I will have to respectfully disagree with you on the Plecostomus. About a year and half ago all my fish died, but the Plecostomus. I was not that educated on fish or aquariums. I thought it would live on the algee that grew alone, So I never fed it. For about one year it lived on the tanks own eco system, and grew! Kept it colors and was active. The Plecostomus seemed to love the tank all to himeself. Granted now I feed him algee pellets, but didnt know otherwise before!

  • Phil says:

    Also, some of these fish live a really long time!

    One thing that bothers me is the goldfish that you “win” at the fair. Totally irresponsible.

    Thanks for the article!

  • Jack says:

    I do have almost all of these fish and they arent as bad as you would think. They do get big but if you live in a house with a back yard then you can do what ever my friend is getting a arapiama for his pond and he has a huge pond in his backyard. It really just comes down to do you have the money, space and time to take care of these fish.

  • MRMAN says:

    And mantis shrimp. You forgot about mantis shrimp.

  • Carlo says:

    You forgot Clown knife Fish..,


    Thank you very much bro.I am also a fish lover. my aquarium have 160gal. capacity. my favorite fish is KOI cup and Tiger shark. by the influence of the shop keeper i buy two 8”inch sucker. But now I think I need to Keep them out.

  • Jim Tom says:

    Black Ghost Knife should be on here

  • Ryan says:

    Why are mantis shrimp mentioned?

    • TankTerrors says:

      We’ve seen reports of them breaking glass. It might not be common but that alone is enough to make them a risky aquarium pet.

  • Bill says:

    My aunt loves her sucker fish. Shes’ had it 17 years.

  • Amanda says:

    I would have to disagree with the pleco being on the list. Just becuase there are different species that grow only 6 inches long and are perfect for tanks. One species that comes to mind is the Bristlenose pleco. They are great cleaners and can really add some value to the bottom feeder aspect of a tank.

    Do you agree?

    • TankTerrors says:

      Yes, I agree. This list is only highlighting the “Common” pleco which can reach huge sizes. All of the small and dwarf species can make great aquarium fish.

  • Dr.sajad says:

    I think list is really helpful.i recently got a tank
    With three goldens one good sized sucker
    And few others.these suckers really sucks….
    Lot of poop

  • Aden says:

    may I ask, is there a chiclid that is not mean?

  • Mike says:

    I Am new to this aquarium thing and it’s been trial and error I recently bought 3 silvertip catfish and of course they didn’t tell me about these fish they seemed to do well for 3 or 4 days with the other fish but in the last 3 days two died they seemed to fine and my other fish seemed to leave them alone. Do u have a guess of what is wrong? And my water is perfect..

    • TankTerrors says:

      If it is the fish I think, then it needed brackish water.

      • kragok00 says:

        They are fresh water from the store. Get a hydrometer and add salt. Make sure it’s marine salt not aquarium salt. I kept mine at about 1.008 for months when they were young and then moved them up to full salt and now fluctuate salinity slowly. Just make sure you make changes slowly so they acclimate and they should be good to go.

  • Linz says:

    This is a cool list. I haven’t seen a lot of them before but good to know. I have bought a lot of fish from petco in the past and they are terrible at letting people know about what they are buying. Some of them even claim to be fish professionals. Its sad how much wrong information I have gotten from them at petco. I have been told I can’t have certain fish together and later find out they were wrong. One time they told me something was totally ok to do and later on we had big problems because of the bad information. I learned my lesson- do homework and don’t rely on the person you are buying from to educate you. Sometimes they might be right but more often then not they seem to be wrong. Now I go look and then research my choices before going back to purchase them. Always a good idea to look up diets, compatibility with other fish, water temps, max size they will grow, size of tank needed and all that other good stuff. Now that I do research I know what to do and what to buy or not buy. Its nice to reduce the number of fatalities in your tank by knowing what you are doing before you do it.

  • kragok00 says:

    I have the Columbian cats. It’s my favorite tank by far. I fluctuate the salinity every couple months to mimic nature and they are happy active and they never stop moving. You can keep mollies with them until they get larger. But they are active enough on their own to fill up visual space in the tank anyway. I wouldnt recommend them unless your willing to put in the extra work. But they are amazing fish. If your looking for something easier but similar I’d suggest pictus cats who are just as active but stay smaller

  • akki says:

    Nice list bro. Just a quick question.. I have silver arowana. I wish to add more. How many i can keep in my 6*3 ft tank.. Current one is just 8 inches

    • TankTerrors says:

      That is entirely up to personal preference. I would let this one get to a much larger size before you decide. It may look tiny in the tank now but at 2′ long it will fill it up a lot more.

  • Chethan says:

    Is bloodworms r good to oskar and other fish’s

  • Lynn says:

    I’d rather see a blue tang on this list than a bumblebee grouper. Blue tangs can’t be bred in captivity and are almost extinct in the wild. People dumb enough to buy a grouper probably shouldn’t have a tank and if they do, I hope they enjoy their dinner because even I, a non-fisherman, have heard of a bumblebee grouper.

    • TankTerrors says:

      They are a bit more complex being Saltwater fish and not exactly beginner friendly but they only reach 1′ or so. So a good sized tank would hold one no problem as many people do. It would fit more on a Top 10 not for beginners or small tank list than this one.

    • Jonathan Roberts says:

      If you have a large enough aquarium to accomadate the species you choose why not buy one? I Live in the uk and have a heated pool set up for 2 alligator gars which are currently exeeding 8ft in lengh. People should not be told “oh its a stupid idea”, but should be told to ensure they have the space before considering a species!

      • TankTerrors says:

        I would love to see some photos of your 8′ gar, that would be similar to world record size. So I think you are either exaggerating greatly or just making stuff up to sound cool.

  • Jonathan Roberts says:

    Wow this guy/girl seriously has no clue. Plecs, goldfish, pacu, paroon shark, collumbian shark…. these guys only grow massive when living in a massive tank, in which case who cares. Their filter system should be more than adeqate to deal with the “dirt”. Plecks are the best fish for algea clearence, which is generally why people buy them. Im not even bothering to say more because i have no doubt this comment wont even be posted!

    • TankTerrors says:

      I will gladly post it, even though you are incorrect. The only reason a fish will not outgrow a tank is lack of maintenance leading to an early death and stunted growth. You could not be anymore incorrect.

Leave a Reply to TankTerrors Cancel reply