A special oxygen pump is generally used to hit oxygen for fish, and the oxygen pump is placed at a position lower than the fish tank, and then the air head is put into the water. Under normal circumstances, special oxygenation equipment is needed only for raising large fish. If it is a small fish, the feeding density will not be very high, and regular water change can achieve oxygenation effect. However, the oxygen consumption of big fish is relatively high. If oxygen is insufficient, it is easy to threaten its survival.

1. Goldfish: Goldfish is a very common ornamental fish, which has a long culture history in China, with many varieties and different personalities. It is usually divided into four species, namely grass species, culture species, dragon species and egg species. No matter what kind of goldfish, the consumption of oxygen is not high, so it is perfect to raise it in a fish tank without oxygen.

2. Betta: Betta is a aggressive fish known by its name. This kind of fish usually cannot be mixed. Two male betta will fight together, so it can only be raised alone. However, as a fish of the family Percidae, one of its major characteristics is the suprambranchial organ, which can make it swim to the water surface to breathe in an environment with low dissolved oxygen, so it can also be raised in a fish tank with low oxygen.

3. Guppy: Guppy is a common small tropical fish. Its length is only 3-4 cm, and its demand for oxygen is not high, so it can be fed in a fish tank without oxygen. The tail of this kind of fish is very big and beautiful. When it is raised artificially, it is necessary to prevent diseases such as needle tail, otherwise it will greatly reduce its ornamental value.