The easiest way to judge the age of a fish is to look at its scales. Fish scales are like annual rings, which are circled round and round, usually bright and dark. The bright circles represent its growth period, which is often thick, while the dark ones are usually very thin when it stops growing in autumn and winter. This represents a year, and you can know how big it is by counting laps.

1. Arowana: Arowana is a large ornamental fish, so its life span is relatively long, usually between 15 and 20 years, and some species can even be raised for 30-40 years. This kind of fish has beautiful posture, shiny scales and fierce temperament, and usually feeds on fish, shrimp and aquatic insects.

2. Swallow fish: Swallow fish, also known as fairy fish, is a popular tropical fish. Its dorsal fin and anal fin are very long, and its pelvic fin is filamentous, which looks like a swallow. The life span of this kind of fish is generally about 5 or 6 years, but the life span of artificial breeding is only 3 years because of inbreeding.

3. Goldfish: As the most common ornamental fish in China, goldfish has a long history of cultivation, and its life span is longer than that of fish of the same size, usually living for about 7 years. Of course, the life span of this kind of fish is also affected by the feeding conditions. If it is well raised, it will live longer, and the longest record is 31 years.

4, Koi: Koi itself is a kind of carp, and its life span is similar to that of carp, which can reach 60-70 years, and it is the longest among ornamental fish at present. This kind of fish has miscellaneous feeding habits, mild nature and easy feeding. As a wide-temperature fish, it has strong adaptability to water temperature.