You have just purchased your first aquarium. Now what fish should to buy. Well I would suggest tetras and maybe some guppies especially if it is your first venture into owning an aquarium. If your tank is small these are the perfect fish for a small tank. Avoid goldfish. Goldfish are from the carp breed which means they can and usually grow very large. They can end up eating any other fish in the tank. I would also suggest a Plecostomus. These fish look like a small catfish. Don’t worry they don’t sting! They are very docile fish, and no matter how big they get, they will never eat another fish. They are algae eaters, and will eat any algae that grows in your tank.