ok, please don't think I'm dumb but what other fish are there besides tropical?
Hey now, no one here will ever think you are dumb, just so you know
. As per your question yes there certainly is.
There are marine fish (...do not even think of going here
),
and there are native species, like sunfish that you find in ponds around you, but I wouldn't suggest these for 10G- maybe a 20 though. This is the cheapest route I think as you don't *need* a heater (but it is recommended) and you don't have to pay for any fish- you catch it yourself! IMO they can be just as beautiful as a tropical as well.
Anyways there are also goldfish, but as stated earlier they need a lot of room per fish and are very messy, an thus hard to take care of properly.
That leaves tropicals. These fish cover a very broad spectrum from Amazonian fish, to Asian fish, to African cichlids, to a few Australian fish. The most common I have informally observed are the Amazonian fish, as these are generally very colourful and small and easy for beginners. This group includes many small tetras and bottom feeders that will form a school and swim in one big group and are easy to take care of. I personally have guppies (male and females... man am I ever overrun with babies :S) and neon tetras. I love the tetras and how the swim around together in a little group.
If I could throw my advice into this maelstrom I would say to go for a 20G tank (this is what I have and started with and I am glad I didn't go any other route) with a couple cory catfish (small comical bottom feeders that love small groups of their own kind, playing tag with each other) and maybe 5-7 of two types of tetra, like cardinals, black skirts, neons, or the same number of rasboras like the harlequin rasbora. That would give you ten fish of two types/colours that will school with their own kind, with some comical bottom feeders. This is just my advice. My more specific choice would be
3-5 small cories (sorry, I don't know how big each type gets as I tend to get shrimp for my bottom feeders),
7 cardinal tetras(very colourful and relatively hardy fish) and
5 black skirts (interesting shape and get fairly good sized for a tetra). Someone will come on and say its a bad idea I am sure but this is my opinion
. But as I am sure you know, make sure your son picks the stuff out, including the fish. I would suggest my list as a guideline, but if your son doesn't like them then go for what he likes, making sure the choices are good and sensible.
One pumpkinseed sunfish would be great in a 20G tank- they are absolutely beautiful IMO and they cost nothing and are VERY hardy fish. However, it is winter so please don't go try to catch one, and they could prove to be very elusive for you to catch. Also with only one fish in the tank your son may get slightly bored. My above tropical choices are keeping your son in mind, as well as you.