1. Reason: If guppies are often not given water during feeding. Then the feces discharged by guppies will accumulate in the water, which will lead to the deterioration of the water body. At this time, their bodies will turn black.

2. Treatment method: Firstly, the guppy is fished out of the original fish tank, soaked in the fish tank with potassium permanganate for about half an hour, and the fish tank is sterilized. Then replace a quarter of the water in the fish tank. Finally, they are raised in fish tanks.

1. Reason: Guppy is a tropical fish, and they need to live in a higher water temperature. If they are raised at a lower rate, they will swim slowly and suffer from anorexia. Finally, the body will become black.

2. Treatment: Place a heating rod horizontally in the water and open the heating rod. Slowly raise the temperature in the fish tank until about 25 ℃.

1. Reason: When guppies are infected with needle tail disease virus and suffer from needle tail disease, their bodies will also appear blackening.

2. Treatment: First, fish out all the fish and separate the diseased fish from the healthy fish. Then sterilize the fish tank and put healthy fish into it. Then put a small amount of crude salt in a new fish tank, adjust the concentration of salt water to about 3%, and soak the sick fish for about 20 minutes every day for treatment, and then return to normal after a period of time.