How did arowana's back turn blue and black?

1, caused by back injury;

2. The water temperature is abnormal. It is recommended not to change water frequently. Yinlong has high requirements on water temperature and environment. Try not to change things he is familiar with frequently.

Arowana (arowana), also known as whitebait, whitebait and arowana, is native to Amazon River Basin in South America, Nile River Basin in Africa, Australia and Papua New Guinea. Generally, they live in ponds of tributaries and submerged bushes on the shore, and sometimes they can be found in water environment with floating grass. After flowing into China, arowana has been successfully propagated in the south, and it is one of the main ornamental fish in China. Arowana is quite popular in Southeast Asia because of its feng shui demand.