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11 Freshwater Fish Beginning Fishkeepers Should Avoid

While these fish can be kept, they are more challenging to keep for those new to the hobby.

By John B. Virata | September 13, 2013

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Beginner aquarists are sometimes in the dark when it comes to choosing fish. They look at fish at the store and are often unaware that the little sucker mouth catfish with a body of armor can grow to more than a foot in length and live for 20 years. Did you know that those cute orange and white (and black) oscars will get very large and unload lots of poop in the tank? Most beginners don't. 

So what fish should beginner fishkeepers generally avoid altogether?

Here is a rundown of 11 fish that are so popular even the largest retail store in the world sells some of them in its pet section. If you are a beginner, you should generally avoid these fish, at least until you get the hang of keeping fish and maintaining your tank properly. You can set up species specific or specialized tanks when you get your proverbial feet wet in the hobby. These fish are generally not the best beginner fish, and demand and require a bit more of what a community tank can offer. They generally require stringent and specialized water quality requirements, or better filtration, or must be reconsidered due to their aggressive behavior or tank busting physical traits. So, in no particular order, here they are.

Pacu
Pacu. Photo by Omnitarian/Wikipedia

Pacu (Colossoma Spp.)
The pacu is often sold as the vegetarian cousin of the piranha. Both belong to the same family of fish, Characidae. The pacu however has one different characteristic, and that is the size of the fish when it reaches maturity. And this is where an unsuspecting beginning fishkeeper gets fooled. Most pacu that you see in your local fish store are just 2 to 3 inches in length with nice coloration. However, these fish will outgrow a 55 gallon tank in their first year and will continue growing, often exceeding 10 pounds in weight. And their colors will fade. Unless you have a nice-sized outdoor pond, avoid this fish, and avoid any local fish store that will sell you one without telling you how big this fish gets.

Red-tailed shark
Red-tailed shark. Photo by Aaron Norman
Red-tailed Shark (Epalzeorhynchos bicolor)
The red-tailed shark is a hugely popular fish in the hobby because of its striking coloration and a body that resembles a shark. It made it to the list not because it is difficult to care for, which it is not for the most part, but due to its highly territorial nature. The red-tailed shark won't tolerate other red-tailed sharks in the tank or similar species such as the rainbow shark, and I've kept certain individuals over the years that have harassed smaller fish in my community tanks, which is often how beginner fishkeepers set up their first tanks. If you do choose to keep this fish, ensure that your tank isn't populated with timid individuals as they may suffer from this shark. plecostomus
Plecostomus can grow to more than 12 inches in length. Photo by Aaron Norman

Plecostomus
Got an algae problem? Get a plecostomus. That is often the solution to many folks' algae issues, rather than determining what is causing the algae in the first place. The plecostomus is such a popular fish that even the largest discount retailer in the world stocks them for sale in their aquariums. But they are often always small specimens no more than three or four inches in length. Beware this fish. It will grow big. Very big. Most beginners start off with a 20 to 30 gallon fish tank. Adding a plecostomus to such a tank is like housing a killer whale in a swimming pool. The plecostomus can grow to 12 inches and larger. I've seen huge specimens (former pets that were released) schooling in Manoa creek on O'ahu, dining on algae). And not to mention, they are gross polluters, meaning, they poop a lot.

Oscar
Oscar. Photo by Al Castro

Oscar (Astronotus ocellatus)
The oscar is another species that the largest discount retailer stocks in its sparse aquariums and can be purchased at virtually every local pet store and big box pet store. They are always available as juveniles in normal (black and orange) and albino colorations. This fish requires a tank of 50 gallons or more, with 80 to 100 gallons a good size, not a typical beginner tank sized setup. A member of the cichlid family, the oscar will eat virtually any fish that it can fit in its mouth, and because of this, some of those who keep them feed them goldfish and other small fish, even though this is not necessary. For beginners, this fish may be too much to handle. It is large and as such needs a specialized tank for large fish.

Neolamprologus cylindricus
Neolamprologus cylindricus. Photo by Regani/Wikimedia

African Cichild
African cichlids of the Rift Lakes are in my opinion the most beautiful fish in the freshwater hobby. The problem with them is their aggressiveness. Beginners may not take to their behavior and will certainly be upset when their community tank fish are ripped to shreds by these cichlids. They will certainly kill most any species of fish housed with them, and are often seen fighting with each other as well. Beginning aquarist may like their beauty but they are best left to intermediate and advanced aquarists due to their territorial nature, specialized care, and their need for weekly water changes.

Silver arowana
Silver arowana. Photo by Al Castro

Silver Arowana (Osteoglossum bicirrhosum)
The silver arowana is another fish that is often sold as a juvenile to unsuspecting fishkeepers who have no idea with regard to how big this fish gets. As with the Oscar and other "tank busting" fish, the arowana will eat virtually anything it can fit into its mouth, needs a fairly large and long aquarium with the general ideal aquarium being three times the length (it can grow to 3 feet in length) of the arowana. While they are cute when small, the arowana grows into a monster fish with a massive appetite and bioload to boot.

Bala shark
Bala shark. Photo by Aaron Norman

Bala Shark (Balantiocheilus melanopterus)
Another popular fish due to its shark-like look, the bala shark is actually a member of the Cyprinidae family and is closely related to carps and true minnows. The bala shark can grow to 12 inches in length or more, again too big for those new to fishkeeping and too big for your average community aquarium. Other than its large adult size, the bala shark is generally a very peaceful fish that does best in groups of six or more.

Discus
Discus. Photo by Al Castro

Discus (Symphysodon aequifasciatus, S. heckel and S. haraldi)
As with the African cichlids, the discus is on most aquarists list as one of the most beautiful fish in the hobby, freshwater or saltwater. A very peaceful fish with a calm demeanor, the discus requires more specialized care than most other beginner community fish. It requires very specific water parameters, a large tall tank with plenty of live floating and rooted plants, and a strict partial water change schedule. Because of these requirements, discus fish are best left to intermediate and advanced aquarium fishkeepers.

Glass catfish
Glass catfish. Photo by Al Castro

Glass Catfish (Kryptopterus bicirrhis)
Glass catfish are very interesting and cool fish to look at as their bodies are transparent and completely see-through. Found in virtually every fish store and big box pet store, most glass catfish are wild caught. They are very susceptible to bacterial infections. The glass cat is a shoaling fish and should be kept in groups of at least six. Anything less and they are prone to perish in a community tank.

Otocinclus
Otocinclus. Photo by Rainer Schmitt/Wikimedia

Otocinclus (Otocinclus sp.)
Otocinclus are a delicate sucker mouth catfish species that requires absolutely pristine and well agitated water to mimic their habitat in the wild. This fish is also primarily wild caught and as such are more challenging to keep than captive bred fish, though they can be kept successfully. The otocinclus requires a densely planted tank with plenty of live plants, rocks and a fine substrate. This herbivorous fish requires a supplement of raw leafy vegetables such as romaine lettuce, zucchini and peas to add to the algae tablets that most people who keep these fish feed them. If you can provide excellent water quality and supplement their food with vegetable matter, you can be successful with this fish.

Koi
Koi. Photo by John B.Virata

Koi (Cyprinus carpio) Koi are often seen in water gardens and backyard ponds because you guessed it, that is where they will flourish, not a fish tank. The koi is basically a beautiful carp that can grow to several pounds and up to 2 feet in length. They require 100 to 200 gallons of water per adult fish, way more than most aquariums can provide, let alone aquariums for beginners. It made it to the list because they are often seen at your local fish store and big box store for sale in fish tanks and people assume that is where they can be housed when they take them home.

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11 Freshwater Fish Beginning Fishkeepers Should Avoid

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Reader Comments

Ash    International

6/9/2015 4:30:48 AM

I've looked at a couple of other websites & they, while mentioning that African Cichlids are aggressive, they do recommend them for beginners. So I'm now a little confused....

Hamza    International

5/11/2015 7:01:21 PM

This article was really good and very informative. If someone interested in seeing another related article on Aquarium Fish, here is the link to visit LINK

Brendan    International

4/20/2015 8:52:21 AM

I have two plecostomust and two glass catfish and they are doing fine in my 25 gallon tank. And do you have any recomdations for a community puffer

Matthew    Cambridge, MA

1/4/2015 10:18:06 AM

I understand seasoned aquarists concerns for fish in new aquarists tanks, however, I would play devil's advocate in stating that I do not believe that any fish is too difficult for a beginner aquarist.

All fish have water parameter requirements, and their own needs, and it is true that some fish have more strict needs than others, however, with properly educating oneself and learning as much about a species prior to purchasing a fish, anyone can successfully start a tank with the most needy of fish, beginner or seasoned aquarist. The key is to really become knowledgable about the fish you are purchasing first, and to be willing to meet the fishes needs and to spend the time needed to do that.

A better title for this article would be something along the lines of "Fish that need extra care," or something to that affect; maybe even, "Aquarists beware."

When I first began keeping fish, I spoke with many people on fish forums about their opinions of the different fish, and I was discouraged to the number of negative comments there were. Instead of offering help and advice, people told me that all of the fish I wanted were not suited for beginners, and I had no place in getting those fish; they told me to start with something more simple like tetras. With everyone telling me that I shouldn't be getting these fish, discus, and no one offered any advise, I did as much research about the fish I could myself, and I have now been successfully keeping discus and some other more difficult fish for quite some time now with no problems, and no deaths.

If I were to help a new aquarist in their endeavors, I would not steer them away from any particular fish, but rather would help them research, and meet the requirements for any fish they so desired to care for. Research and the ability to put the time in to caring for any fish is the most important part about keeping healthy, and beautiful fish, no matter the level of aquarist.

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