The general rule of thumb for fish is about 1in of fish per 1 gallon of tank. Some species it's a bit different, you can ask most of the people at something like a petco and they can help. Actually smart kids there...
Don't bother with neon tetras, as they die quick. Same with those 'baby sharks'. Mollies, Guppies and Goldfish are always awesome. And get a sucker fish if you don't want to have to clean the tank constantly.
Small tank probably means bowl. But, if you can get away with a 10 gal tank, thats a decent size to have. If you can only get the bowl, try a male Betta. ONLY ONE!! ! They kill each other if in the same tank. But they are very pretty. Get one who's fins aren't shredded to snot, as he's in better shape and not on the verge of death. Learned that one the hard way.
Also, if they don't allow a larger tank, save some money and go to the home decor section of a WalMart and grab one of those dorky vases you see there that you're supposed to put pretty rocks in. WAY cheaper than an actual fish bowl.
Don't over stuff the tank with loads of plants. Do try and get a plastic backdrop, fish seem to be less scared of their tank when you have one. And don't get a tank you caint lift, cause at some point you need to clean it, and dropping your nice glass tank is kinda a bummer. There are siphon kits sold next to the fish, get one with a screen so you can empty the tank from time to time, because no matter how clear the water is, it does become stale.
Don't bother with a bubbler unless you getting a tank bigger than ten gal, it's more of an annoyance to the fish than it helps. Filters are always a nice bet, they help keep the tank from smelling like sushi.
Fish really do hate long car rides, so unless you must, buy them close to their new home. They also hate bouncing in the waves for any length of time, as they are accustomed to the nice safe tank. So wrap them in a soft blanket and set them in the least bouncy spot in the car.
I hope I haven't been to babbly, I know loads about fish from mum and my old friend who works in a specialty shop. So if you have a question I didn't answer, as me, I ought know or can point you somewhere that does.
PS: As pretty as they are, if this is your first tank, DO NOT get saltwater fish. They are tricky buggers to keep alive. Once you get a better idea of how your enviroment is, then you can get them.
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