The best small cold water fish to keep is goldfish. It is a traditional ornamental fish in China, with a history of more than 1700 years. It is cultivated by crucian carp. It has many varieties, different shapes and rich colors. It is usually divided into four lines, namely grass species, culture species, dragon species and egg species, among which grass species goldfish is the most common species, and it is also the easiest to raise. Culture species and dragon species have slightly higher requirements, and egg species are the most painstaking.

1. Feeding: Pay attention to feeding first when raising goldfish. As an omnivorous fish, it can accept a lot of food, and it can be fed regularly and quantitatively with fish food, such as various pellet feeds or thin slices. It can be fed three times a day, in the morning, middle and evening, and it is advisable to ensure that the fish are eaten within 3-5 minutes after each feeding.

2. Change water: In order to ensure the health of fish, change water regularly. The cycle of water change is related to the maintenance of water quality. If there is filtration and the water quality is well maintained, the water can be changed once a week or two. If the fish tank is small and the water quality is not easy to maintain, it should be changed every three to five days, with a quarter of each time.

3. Oxygenation: Although goldfish is small in size and does not have a particularly high demand for oxygen, if the feeding density is relatively high, it is best to use oxygen pump for oxygenation all day. Oxygenation not only helps goldfish breathe, but also accelerates metabolism, which is also helpful to maintain water quality.