Qualities for oddball?

Hi,
Many people would consider Killifish and Rainbow fish as oddballs? I used to disagree, but I've ran into too many people who think so. Here was my first thought about "qualifications" to oddballs: fish that are reclusive from other families or fish so cannot be sorted into any of the categories (such as characins, cyprinids, etc); miscellaneous/extra/others fish. Eeels and Puffers are completely different fish but are both considered an oddball. Would killifish, rainbow, pleco, gars, pencilfish, etc. be considered oddballs?
What is your idea about oddball qualifications?
Answers:
In my own opinion, oddballs are fish that tend to be uncommon. Or at least uncommonly kept by the vast majority of aquarists or beginner aquarists. They tend to be ones that people don't know much about. Something along the lines of knife fishes, certain freshwater gobies like knight gobies, butterflyfish, bushfish, and the like.
They tend to have unique shapes and unique habits. They don't necessarily have to be colorful, just that they stick out from the rest of the fish in a tank. They also tend to be a bit on the pricey side. I got my african butteflyfish for $8 (reg. price $15), my striped peacock eel for the same, my knight goby for about $5 but they tend to cost around $10 where i am and my leopard bushfish for $10 but usually around $15

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I wouldn't consider rainbow fish or most killifish as oddballs. An oddball to me is something very limited and unique. Electric eel, electric catfish, lungfish, 4 eyed fish, mud skippers, bowfin, (maybe sculpins), babywhale elephant nose black ghost knife and the other sonar fish. I'm sure there are others. You might be able to argue that some fish could be considered oddballs due to their breeding behavior though I usually just consider the fish itself an oddball and don't factor breeding into it. I do not consider a group of fish as large and generally similar to most other types of fish as the rainbow fish family being oddballs. I think it was Tropical Fish Hobbyist (TFH) that recently had an issue devoted to Oddballs. I know there have been a few books dedicated to this as well.

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Odd balls are those fish you see at a fish store and go damn that looks weird, Fish that you don't see in movies or tv.
Most oddballs are tank busters, such as arowanas, clown knives, red tailed catfish.
Some are even cool to see such as the needle nose gar who eats small fish.

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I guess it would depend on a few thing but first qualify oddball. Oddball in nature, in the hobby or in pet stores. If you mena in petstores, then Killifish would certainly qualify, but then aren't we just talking about rarely mass marketed? Odd in the hobby, some killifish would qualify and some not, but then the puffer wouldn't for example because it's actually fairly common in the hobby. Killifish might meet that definition on the US, but not for example in the former Soviet Union where they are much more common.
If you mean in nature because it's so different than many ofther fishes then puffers would certainly qualify, but I'm not sure I would call killifish as a group into that oddball classification because after all, a small percentage of them are actually annual fish, while the rest function just like many other fish and are just another group of egg scattering fishes found around the world.
Killifish are also a fairly large group of fish and with so many fish bearing that name, can you really define them all as oddball? I would define oddball as a fish that has traits not shared by very many species, such as puffers and lungfish.
MM