Freshwater fish that can be kept alone

sure! oscars, for one.. terrors, needlenose gars, a few more of the predatory fish will do fine alone..
 
Bettas are easy to keep in a tank alone and do well because of being labyrinth fish. Just about any fish can be kept alone, but some like botias do better in social groups and should not be kept alone. Cichlids do well alone and can be trained to eat from your fingers like a dog. Gouramis tend to have unique personalities when kept alone and they get to know their keeper. A woman I work with had a harlequin rasbora in a 1 gallon on her desk for a very long time. I'm pretty sure the only reason it died was when the power was out post-katrina.
 
The majority of fishes can be kept alone, and would most likely do better with all the space to themself. The only fishes that won't do well alone (obviously) are schooling and shoaling fishes that need company of their own species for "comfort."
 
It depends on what kind of tank you want. If you want a 5-10 gallon aquarium, then you can get a Dwarf Gourami. If you get a big tank like a 75 gallon tank, you can get an Oscar. If you have a 20, you can get a goldfish. It really depends on the tank you have and what you want.
 
Get a BIG tank and get your self a nice arowana. Or a fire eel. Don't be fooled by the cute little ones you see in the pet store, I've seen 36" long 6" thick fire eels. The cool thing about raising one that big would be hand feeding them then. Mine would curl up in my hand and eat blood worms out of my fingers. But then I saw the huge ones at the Shedd Aquarium in chicago, came home and gave mine away.
 
Bass are pretty cool and will be alone no matter how many other fish you have in a tank, they have no socolisation with other animals at all unless spawning. After spawning the parent fish cease to recognize each other and even eat their own young. You would need a hefty tank though because they are illegal to keep under 14" or so. Arowanas are cool but they get like 6' long...
 
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