Selecting the best goldfish bowl can depend on the type of fish you want to keep in it. Goldfish are actually not well suited to life in the bowls that are named after them, as they can quickly outgrow the cramped space. If you absolutely must keep a goldfish in a bowl, then you should select the largest bowl you have space for. A goldfish bowl that is 1 gallon (about 3.7 lt) in size will typically be big enough for a juvenile fish. If you prefer a smaller goldfish bowl, then you should choose a smaller fish that will be able to survive in those conditions.
Goldfish bowls are one of the simplest ways to keep fish, though they typically provide an unhealthy environment. That is due to the fact that bowls, unlike traditional aquariums, lack any method of filtration or aeration. If the water in the bowl is not changed regularly, waste products from the fish will build up very quickly. The water can also stagnate, making it very difficult for the fish to breath.
If you want to select the best goldfish bowl, then you need to consider the type of fish you want to place in it. Goldfish start off very small, but they can grow quite large, and will live for decades under the right circumstances. If you keep the water in your bowl very clean, and feed your goldfish a healthy diet, it will typically outgrow the bowl before long. That makes it important to choose the largest bowl you have space for. A 1 gallon (about 3.7 lt) bowl will be sufficient for a fish that is 2 inches (about 5 cm) in length, but goldfish can grow much larger than that.
Another factor to consider when choosing a goldfish bowl is the surface area of the water. Goldfish require a substantial surface area for oxygen to absorb into the water, so keep that in mind when looking for a bowl. If you choose a spherical bowl that has a narrow top, it is important to only fill it about halfway. That will maximize the surface area of the water, which can help your goldfish breath.
Some fish, such as bettas and guppies, are better suited to life in goldfish bowls. It is still important to change the water regularly, but these fish are smaller, do not grow to large sizes, and can sometimes even be kept in pairs. You should still provide about 0.5 gallons (around 1.8 lt) of water for each inch (about 2.5 cm) of fish length, but bettas can sometimes survive in a goldfish bowl that is substantially smaller than that.