Koi is not afraid of heat. Generally, fish farmers like to call koi and goldfish cold water fish, which is opposite to tropical fish, but they are not real cold water fish. Real cold water fish can only live in water environment below 20 ℃, while koi is a wide-temperature fish, which has a wide range of adaptation to water temperature and can survive in environment of 5-30 ℃. Generally, it is not afraid of heat unless the temperature exceeds 35 ℃.

1. Arowana: Arowana is a primitive freshwater fish with a body length of about 50 cm and a life span of several decades. It is gentle and fierce, mainly feeding on fish and shrimp, and has high requirements on temperature. Generally, the water temperature should be maintained above 24 ℃, and the low temperature will limit its growth.

2. Parrot fish: Parrot fish is an artificially cultivated ornamental fish. Like mules, it is a cross between two similar fish, so it has no reproductive ability. It also belongs to tropical fish, which has certain requirements for water temperature. The decrease of temperature will lead to its dark color, which seriously affects the ornamental value.

3. Guppies: Guppies are small tropical fish. They come in many kinds and colors, but they all have a beautiful big tail. As a tropical fish that can endure low temperature, it can survive in the environment of 16 ℃, but it is best to control the water temperature above 20 ℃ with a heating rod to avoid the fish being affected.