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


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