Is there a way

[Synirr]

What do you mean swim comfortably?

Have enough room to stretch their fins
Some fish prefer more swimming space than others, and danios are one of those fish.

 

[Dorkhedeos]

im sure you can, but i dont think they will be as fun to watch cause they will have to turn more often. im sure they will survive, but i dont think they will like it. but no fish likes to be in a box anyways.