westward13...
There shouldn't be any problem keeping a Rope Fish
Erpetoichthys calabaricus with a
Polypterus senegalus as long as the Rope Fish is larger. I've got a grow-out tank right now that has 5 young
P. senegalus in it ranging in size from 3 - 4 inches. There's also a Rope Fish in there that is about 9 inches long but not much bigger around than the
senegalus. They're all getting along just fine.
Personally, I wouldn't keep a 'pleco' type of cat with bichirs. Though I personally haven't experienced it (I've never kept them together), there are reports of the 'pleco' rasping on the hard ganoid scales of the bichirs and causing damage that leads to infections. I like my bichirs too much to risk it.
Your 75 gallon will easily house the
Polypterus and
Erpetoichthys...though I'll predict that as they grow you'll begin to notice the Cory cats and Swordtails start to disappear. Eventually the Danios will disappear as well, though the Gouramis will probably manage to hang on successfully. While Swordtails and Danios are much faster than the bichirs....the bichirs hunt at night when the other fish are asleep and immobile. If you decide you want a bichir tank then you could quite easily house a couple more good-sized
Polypterus individuals as well....especially some of the 'smaller' species like
senegalus, palmas, polli, retropinnis and even
delhezi. Larger beasts like
endlicheri, lapradei, bichir and
ornatipinnis might eventually feel a little cramped.
Hope this helps!
