Looking for ideas

[duanes]

Since the tank is mostly Asian, I would opt for a couple small archer fish.
If being geographically correct is not an issue, an Anableps would also occupy that upper tier.

 

[HarleyK]

This would be strictly upper level, as in: Surface. But your son, depending on age and tank location, might be the perfect height to view and watch it: Pantodon buchholzi, the African Butterflyfish. Checks the “oddball” box, for sure.

 

[Fallen_Leaves16]

Since the tank is mostly Asian, I would opt for a couple small archer fish.
If being geographically correct is not an issue, an Anableps would also occupy that upper tier.

Pardon my ignorance, but wouldn't a standard 55G have far too little surface area for either of those species to be relatively comfortable? It was under my impression that most, if not all Toxotes were rather skittish and relied on a rather large footprint to be able to dash about without abruptly crashing, and that Anableps were a rather large, exclusively surface-dwelling brackish species prone to traveling good distances in large groups.
Then again, it's been quite a while since I last kept archerfish, and I don't have nearly enough experience with Anableps to give suitable judgement about their care.

 

[duanes]

Pardon my ignorance, but wouldn't a standard 55G have far too little surface area for either of those species to be relatively comfortable? It was under my impression that most, if not all Toxotes were rather skittish and relied on a rather large footprint to be able to dash about without abruptly crashing, and that Anableps were a rather large, exclusively surface-dwelling brackish species prone to traveling good distances in large groups.
Then again, it's been quite a while since I last kept archerfish, and I don't have nearly enough experience with Anableps to give suitable judgement about their care.

I personally would not put either of these as adults in a 55 either, maybe a 155.
But if juvies, they'd work a while.