Red Tail Barracuda gets around 1'3" in a tank it will be agressive and territorial, if your planning on putting him alone is cool but tank mates will be very hard to have with him.
Birch any type of birch would work well in your size tank, the only caution I will say is that if your looking for an active fish to keep you entertained a birch might not suit you. Some are more active than others but I don't consider them "active" predators.
As knife fish go you could go with a BGK or a Clown, even thought the clown has been known to get around 32" they are nimble and won't have a problem turning in the space provided.
As gars go the only thing I would recommend is a needlenose gar it will get about a foot long and your 2 foot tank should offer it a good enough turning. Even some of the smaller gars will be two big for your tank for life though. A spotted gar can jump from 4in to 16 in a matter of a year and before you know it, it outgrows your tank.
Arows have good turning but do your home work on this beutiful fish as it gets really big. I would probably hold off on one in your situation though, all species of arors get to or exceed 36" when mature.
The only sting ray I would put in your tank would be a Potamotrygon motoro, and again reaserch is needed to be done before owning such an awsome creature.
The fish of choice that I would get is a Large Cichlid such a a motaguense, they have incredible personalities and will not disapoint. You should be careful with tak mates especially if you intend on breeding.
As far as an electric ell goes I don't see that as an option for you.
You can research the Fire Eel (Mastacembelus erthrotaenia), Zig Zag Yellow Tail Eel )Mastacembelus pancalus), or a Tire Track Eel (Mastacembelus armatus) as they would suit your aquarium dimentions.
The Pike I would personally forego and go with a LMB or a SMB although I fing the small mouth bass to be more agressive, the will grow to about 12-15 when mature and are very fun to watch, they hit pray life a freight train
Hope this helps narrow down your selection good luck
