So assuming you are keeping fresh water fish, the first thing you will need is an aquarium. This can be anything that will hold water, preferable with at least one side being clear so you can see into the tank.

The shape and size is important depending on the number and type of fish you wish to keep. Goldfish can grow in excess of a foot length or longer and will need plenty of space, at least 10 gallons for each fish once they reach about 4 inches. However, if you are keeping guppies you can keep 12 in the same 10 gallons.

The shape is important as well. It is always better to buy a rectangular tank then any other shape. These hold the most water for the area they take up, and allow the fish the most swimming space. Glass bowls should be avoided. The main difference here is surface area. Fish breath oxygen which is dissolved into the water through the surface. A rectangle shape tank has a large surface area, a bowl has a very small one.