Sep 21, 2019
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5 Aquarium Fish You Should Carefully Consider Before Purchasing

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While all the fish in this list are unique in look and appearance, they have fairly regimented requirements.

Finding a good local fish store is one of the true keys to success in keeping happy and healthy aquariums. One way to tell if a local fish store (LFS) is good is that whenever you go to buy a fish there they should ask you some questions, including:

  • How big is the tank your new fish are going into?
  • What fish are in this tank, and are they adults or juveniles?
  • Water parameters – temperature, pH, hardness, type of filtration?

You should also ask the staff at the local fish store, and yourself, a few questions, including:

  • How big will these fish get – most fish sold at your LFS are juveniles
  • Will it pick on/eat other fish?
  • Will the fish in the tank they are going in to pick on/eat it?
  • What water parameters does this fish prefer?
  • What does it need for food?
  • Is this fish best kept singly or in schools/shoals?

Given that you have asked/been asked the questions above, let’s discuss some specific fish that look really great and interesting in the LFS, but that have some considerations that may make them unsuitable for your tank(s). The fish we will look at are:

  • Clown Knifefish
  • Glass Catfish
  • Upside Down Catfish
  • Archer Fish
  • Dwarf Puffer

These fish are, indeed, very attractive fish – but before you buy one of them, please consider the following for each of them.

Clown Knifefish (Chitala chitala)

Clown knife fish can grow to more than 2 feet in length.

Clown knife fish sold in an LFS are usually around 4” – 5” long, and incredibly appealing. They have an interesting shape, lovely slate gray color, a few little spots, and an alluring way of hanging in the water simply by rippling the anal fin a bit. Hard to resist – but before you buy a clown knifefish you should consider the following about them: 

  • When mature, they can get to be larger than 24” long, and very hefty. In the Far East, they are a major food fish.
  • Although they do not swim around very actively, they require a large tank, especially as they mature; they eat a lot and produce lots of wastes
  • These fish get that big by eating anything and everything that they can – and their mouth is essentially like a trap door, huge and able to fit good-sized fish into it. While they hang there rippling in the water, they are a true ambush predator and can move with lightning speed when they want to
  • Clown knife fish are very susceptible to fungus, and any scrape or wound can very quickly lead to the demise of the fish

 Glass Catfish (Kryptopterus bicirrhis)

Glass catfish will thrive in a species-specific tank, and will usually perish in community tanks.

What could possibly be more interesting than a “see-through” fish?

That is exactly what the glass catfish is. The flesh of this fish is absolutely transparent, and you can clearly see the fine bones of the spine and ribs, as well as the sac where the internal organs are. Pretty hard not to be tempted to take one home – right? Wrong! Before you buy any glass catfish consider that: 

  • They are very shy and sensitive fish.
  • Glass catfish will be unable to compete with any other fish for food, and if put into an existing community tank they will starve to death.
  • They need to be in schools of at least 6 of their own kind to be happy – more is better
  • Glass catfish are very difficult to keep, and can rapidly succumb to any common disease such as ich or fungus which are curable in other fishes but difficult to cure with glass catfish

If ever there was a fish that should best be kept in a species tank, the glass catfish is that fish. It doesn’t have to be more than a 10-gallon tank, and that size would be fine for 10 – 12 of them. Slow filtration and dense planting will make a perfect tank for glass catfish.

Upside Down Catfish (Various species)

Talking about the “upside-down catfish” is a perfect illustration of the need for scientific names for fishes. There are a number of fishes that go by the name “upside-down catfish” in the hobby, and they can range from 4” to >8” in mature size; fortunately, all of them are pretty much the same when it comes to requirements in the aquarium, and none of them are in any way harmful to other fish. The most common fish that is sold in the LFS as upside-down catfish is Synodontis nigriventris, and the other fish that are sold by the same common name are usually other Synodontis species.

Upside down catfish range in size from 4 to 20 inches in length depending on the species.


Different mature sizes are the primary differences, and because all upside down catfish are nocturnal you may not see this fish often, at least initially after you introduce them to a tank. I have a 300-gallon tank that is a perfect example of this. There are lots of fish in the tank, including many different catfish. I do remember putting a couple “upside-down catfish” into the tank, and after the lights go out there was one about 4” long that would come out to feed. Then, one night, this huge form came from the depths of the tank. It also is an upside-down catfish, but a good 10” long. Synodontis nigriventris is around 4” at maturity. Synodontis angelicus gets to be 20” – and there are other species that get to in between sizes at maturity. In my 300 gallon tank this fish getting that big is no big deal – but if I were keeping it in 20-gallon things would go downhill quickly.

Archer Fish (Toxotes species)

A fish that makes its living by shooting a jet of water at insects (some also say small birds?) on a branch above the water is very attractive. Actually, when you consider the refraction between air and water, taking that into consideration makes it even more interesting. Local fish stores do not often have archerfish in stock, as they pretty much require a species tank with them alone. In addition to requiring live food, usually in the form of live crickets introduced to the tank on small branches out of the water, archerfish typically require brackish water and excellent water quality.

True archer fishes do best in a species aquarium, heavily planted (especially floating plants) and with filtration that does not move the water around too much.

If you do want to keep archerfish, I would recommend a setup similar to a tank that I had for a couple of years. It was a 50-gallon tank, filled ½ way up with water (brackish), and the top half of the tank was set up as a land environment, with plenty of branches, and a waterfall returning the filtered water back to the tank. In addition to a few archerfish (probably Toxotes jaculatrix) I had four mudskippers (one of the species of Periophthalmus) and two four-eyed fish (Anableps anableps). It was a fascinating tank, and the waterfall made from the filter return made the air portion of the tank very humid (as high humidity as possible is required). A close-fitting glass top kept the humidity high.

Unfortunately, it did not keep all the live crickets inside the tank. Even though all three species of fish went absolutely nuts every time live crickets were introduced, a few managed to escape. The end of this very interesting tank was when my wife, Saint Janet (so named for all the stuff she has put up with from me and my fish) tracked down the chirping sounds coming from a kitchen closet to some escaped crickets at the bottom of one of her flower vases.

One final note on archerfish. A new species of archerfish (Toxotes blythii) has been reported. These fish come from Myanmar (Burma), and are found in 100% freshwater.

Dwarf Puffer (Carinotetraodon travancoricus)

If ever there were an instance where it is important to make sure that the fish you are buying is, in fact, the fish you think it is, the dwarf puffer is one. The true dwarf puffer comes from India and lives in completely freshwater. It also is mature at around 1” in size. True dwarf puffers do best in a species aquarium, heavily planted (especially floating plants) and with filtration that does not move the water around too much. As with all puffers, the dwarf puffer prefers various fresh foods, especially snails. These fish have teeth that need to be worn down by crunching on snail shells – and if not provided with snails you may, in fact, have to grind down the puffer’s teeth yourself.

Dwarf Puffers come from India and live in freshwater.

The problem of making sure that the fish you are buying is the true dwarf puffer is so important because most other puffers sold in the hobby a) require a brackish water environment and b) grow to be much larger than 1” – some can get to 8” or larger when mature.

One very interesting thing about the true dwarf puffer is that it has been successfully bred in the home aquarium (and most of the fish that you will find at your local fish store will have been commercially farmed in the Far East). Fry are very small when they become free swimming, and require very small live foods for the first week, after which they can take live baby brine shrimp.

Article Categories:
Aquarium Setups and Care

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