[JDM]

Bolivian ram. Suggested tank minimums:

20 gallons for one fish, 2 fish in a 36 inch tank; 3+ in 48-inch tank.

Read more: Bolivian Ram (Mikrogeophagus altispinosus) Profile

The tetras are a pretty small fish so you could pack in a good number of those. If you were able to add them 5 at a time a couple of weeks apart and you were doing a species tank you could probably get 20 in there to fill the water space.... maybe more if you have a stable balanced setup but you would have to judge that once the 20 were in.

Jeff.

 

[JDM]

Check out some of the hatchetfish, most of those will fit and are small enough that you could have a descent sized group. They stay near the surface generally so you wouldn't just have two kinds of fish competing for the central water area. Maybe some Pygmy hatchet fish up top and the embers mid water, just double check the water parameters to be sure they are compatible... I think they are though.

Jeff.