One of the best things about keeping tropical fishes- particular the smaller varieties, like characins, Danios, and Rasbora- is that you can keep groups, shoals, or schools of these fishes in aquariums to a great effect.
To me, nothing says "tropical fish aquarium" as a group of small tetras, behaving in a similar manner as they do in their natural environment. That speaks to us...giving animals a great experience in our own tanks.
Yet, for a lot of reasons, we don't see full-on schools or shoals of fishes in our aquariums all that much, so when we do- it's incredibly memorable!
I'm not sure why we don't see more large groupings of a single species of fish in our tanks. Maybe it's that we just want to have lots of different species in the limited space we can offer- and having dozens of one fish is a luxurious and decadent use of space! Or, perhaps it's a desire to see the behavioral interplay between diverse species. Maybe it's finances- I can't argue with that! Have you priced Cardinal Tetras lately?
Regardless of what our reasons are, I wish every hobbyist would try a large group of a single species at one point in his or her hobby "career." It's truly an amazing thing to see. And it doesn't have to be a huge, spectacular thing.
I'm all for seeing hobbyists create aggregations of the same species in their aquariums- whether it's 6 Zebra Danios in a 10 gallon tank, or an epic school of 150 Rummynose Tetras in a 200 gallon planted aquarium.
Please just think about this, and the incredible aesthetic and practical benefits of a mono specific aggregation of fish in our tanks!
Have a great weekend..
and stay wet!