Dark Tank

That will be one awesome tank!!! The only thing that comes to my mind is a blind cave fish. I think that is what their called. They have eyes when they are young, but skin grows over them. Very cool. Good Luck!!!

You have set yourself a difficult task, though while I am thinking about you can light the tank with dim red lights as they do in public aquariums. Most cave fish are either protected or just not collected. There are also several species of salamnders, shrimp, and crayfish that are cave dwellers.

Here are just a few of the blind cave fish world wide,
The Mexican cavefish that is common in aquaria, Astanax mexicanus and jordani
cave gudgeon, Mileringa veritas,
Northern blind cave fish, Amblyopsis spelea
Ozark BCF, A. rosae
southern BCF, Typhlichthys subterraneus
blind cusk eel (FW) there are several species, one from Mexico and Belize is Tyhliasina pearsi
blind cave eel, Ophisternon candidum
grotto sculpin, cottus carolinae
Iran cave barb, Iranocypris typhlops
Oman blind cavefish, Garra barreimiae
several blind cave catfish including these from Texas, India, and Brasil, the Satan eurystomus, Horaglanis krishna, and Caecorhamdella brasiliensis
And two of my favorites due to just being odd the asian Sinocyclocheilus hyalinus and S. anattirostrus (pictured)

Those two fish you pictured guppy are wild!

The ones in the pictures are weirder than that, they are cyprinids and as far as I can tell have only been imported for a fish show once a couple years ago.
For a lot of these fish you actually need to go get them.
Some that you can collect fairly easily if you can get there are the cusk eels and brotulids such as the T. pearsei which has been renamed Ogilbia pearsei, it and a couple very similar ones are common in wells, cenotes, and caves in the Yucutan and nothern Belize, they look pretty cool and the same place you find them you find several different shrimp. here is a pic of one from this site http://images.google.com/imgres?img...rev=/images?q=ogilbia&svnum=10&hl=en&lr=&sa=N

that is a pretty damn sweet idea. When i went to dusseldorf aquazoo they had a cave habitat and it had a couple of eyeless fish It also had one 'shaft' of light that looked really cool

theres a picture of my "Cave tank"
it has 4 blind cave tetras and im also using it as a polyepterus grow out tank. i know the pictures crappy but theres alot of rocks and plants that look great under a red light. most lfs carry zebra rocks which have a zebra pattern and i found black and white plastic plants at petco. since the picture was taken ive added a skull to the left side of the tank. i reccomend doing this. its one of my favorite tanks and probly the favorite with friends. they call it the "goth aquarium" lol

How big is your tank??