African Lung Fish

[Oddball]

how big of a tank do you think they need and why?

A large tank is required due to the large size they attain and to be able to maintain proper water quality due to the amount of wastes they produce.

And, trying to keep two in the same tank would be an exercise in futility. Even breeding partners can't tolerate each others presence once spawning is completed.

Here's an idea of what to look forward to with these primitive monsters:

 

[RowingMunkeyCU]

you might also try checking out

http://www.primitivefish.com/Lungfishes.htm

not a tremendous amount of information, but a decent set of pics for the different species.