Why is there white mucus (layered) in koi fish?

Mucus is normal, and the mucus secreted by koi fish is a state of self-protection. Mainly manifested in the fish's emotional tension or the external stimulation of the new environment when changing water. At this time, it is normal for fish to secrete mucus. Note that when the fish secretes mucus, it is also the time when the fish body has the lowest resistance, and it is very vulnerable to bacterial infection and fish diseases. The solution is to observe more, toss less, don't use drugs indiscriminately, raise ecological water, and change 1/3 water on average for 3-5 days, and the fish will be fine after the self-healing period.