With the exception of rummynoses, I’ve never seen schooling activity in tetras.

And you’re right that shoaling fish are shoaling as they would in the wild. It’s just that our tanks aren’t big enough to see that. And for many species, schooling is behavior that reflects a perceived threat. If that threat doesn’t materialize (nothing is trying to catch/eat them) it sometimes relaxes and stops.

In my experience, I’ve had the best actual schooling experience with harlequin rasboras and Denison barbs (probably too big/active for a 40 gallon). Haven’t kept them, but I’m told that exclamation point rasboras will also swim in formation. And they’re small enough that you could probably do a decent amount in a 40.

 

In my limited experience, the rummynose are the best schoolers. My cardinals usually don't seem to be too interested in schooling.

 

My harlequin rasboras are by far my best schoolers. I have a little less than 30 in my 44g and they are constantly schooling with each other across the front of the tank. I have a school of both neons and embers in another tank and when they do decide to school, it's typically all together.

 

Rummynose tetras hands down...

My group of Trigonostigma somphongis tend to stick together quite closely too.

 

My harlequin rasboras are by far my best schoolers. I have a little less than 30 in my 44g and they are constantly schooling with each other across the front of the tank. I have a school of both neons and embers in another tank and when they do decide to school, it's typically all together.

Inspiring! Leanig toward these and the rummynose. I envision 2 schools swimming around my tank. We shall see how realistic that will be.

 

I honestly think those two would look amazing together! Definitely post an update if you do go this route. I'm still only a couple of months into my 44g and it's been so much fun to work with a larger tank.

 

I had six harlequin rasboras in my old 29g and they schooled all the time and just had great personalities. Very hardy fish too. I'm going to be setting up a 75g and they are on the top of my list for sure. I want to get a big group of them to go along with a bigger size schooling fish (maybe either 6-7 roseline sharks or 5-6 boesemani rainbows) and some other undecided fish at this moment.

Good luck with you setup!

 

I agree with Rummynose Tetras. I also have a school of 20ish dwarf amber barbs. They're always together and quite personable. They're probably my favorite fish as they're interesting, lovely to look at, and don't damage my plants.