White Dots on Koi Fish: Causes & Treatment Methods

1. Ichthyophthirius multifiliis (White Spot Disease)

White spot disease is a parasitic infection that commonly affects koi fish, often lodging in their skin, caudal fins, and gills. This parasite feeds on the fish's nutrients, prompting the fish to secrete excessive mucus, which results in the formation of numerous white pustules across the koi's body. Infected koi may exhibit symptoms such as listlessness, reduced activity, gasping at the surface, emaciation, and difficulty breathing. They might also be seen frantically rubbing against aquatic plants or gravel to relieve itching. Typically, within 5 to 10 days, the affected koi can die rapidly.

Treatment Methods:

Since the causative organism is sensitive to high temperatures, the first step is to raise the water temperature to around 30℃ to accelerate the maturation of the spores, allowing them to detach from the fish's surface. Additionally, isolate the infected koi into a separate tank and immerse them in a solution of 1%5% saltwater for several days, or soak them in a solution of 2 parts per million mercuric nitrate for 30 minutes.

2. Water Quality Issues

Failure to regularly change the water in the aquarium or overfeeding can lead to water pollution and eutrophication, fostering the growth of harmful bacteria and parasites. These organisms compete with koi for oxygen, leading to the appearance of white spots on the fish.

Treatment Methods:

Begin by removing the upper layer of clean water from the original tank and transferring it to a clean basin. Then, move the koi to this new environment. Clean and disinfect the tank, fill it with presunlighted water, add onefourth of the original water, and reestablish the filtration system before reintroducing the koi. Regularly change the water in the tank, at least three times a week during summer, replacing 1/4 to 1/3 of the water each time. Be cautious not to change too much water to avoid startling the koi.

3. Aggressive Behavior and Injuries

With their large size and active nature, koi can become aggressive, especially when overcrowded. If injuries are not promptly addressed, especially in poor water quality, the wounds can become infected and lead to the appearance of white spots on the koi's scales.

Handling Methods:

Remove the injured koi to prevent further harassment by other fish. If it must remain in the same tank, consider upgrading to a larger aquarium. Until the wound heals, keep the koi in a quiet area and treat the injury with diluted potassium permanganate to sterilize and disinfect it. Recovery can be expected after a period of time.

Understanding the common causes and treatment methods for white spots on koi can be invaluable. The above suggestions are for reference only, and if they prove ineffective, it is advisable to consult an online veterinary expert.