Why Is My Koi Fish Flashing? Possible Reasons!

Flashing of koi fish is a sign of parasites in the pond, stress due to overcrowding and overfeeding, poor water quality, overexposure to sunlight, or irritation on the fish’s scales.

Like most aquatic species, koi fish doesn’t have fingernails, so they use objects in their surroundings to help them scratch.

Here is a detailed account of why your koi fish could be flashing.

Why Is My Koi Fish Flashing?

When a koi gets itchy or irritated, it starts to perform a unique display called “flashing.”

While flashing, the koi fish will expose its silvery scales, repeatedly and rapidly turn its body back and forth, and start rubbing itself to the sides and bottoms of the pond.

Though koi flashing might leave you a bit puzzled and strange at first, it is their way of communicating the cause of the problem.

The best thing you can do is monitor the koi fish closely and wait for further developments. In case the koi stops flashing but remains inactive and has lost its appetite, it could be a symptom of an illness.

Furthermore, remember that a koi fish possesses lots of colors and not just the muted goldish-orange. When a koi fish flashes, it starts to display its true colors, which could be shades of red and blue.

Be patient if your koi fish is flashing. If the koi fish isn’t suffering or sick, they should stop the behavior on their own.

In case the flashing continues, try to find the root cause of the problem in order to eliminate it before it harms the koi’s health.

Keep reading to learn more about the common causes of koi fish flashing.

Reasons Why My Koi Fish Is Flashing

Is your koi fish acting weird? Is it turning on its side and swimming erratically and rapidly, or is it changing its color?

These changes in a koi fish’s behavior are known as flashing.

Some common causes of why your koi fish is flashing are listed below:

Presence of Parasites

Ponds and tanks are inevitable to parasitic infections. Turtles, frogs, leaves, snakes, and other”pond visitors” can carry parasites into your koi fish pond, setting the stage for an infection.

Viral, bacterial, fungal, and parasitic infections often result in flashing behavior as the koi fish tries to alleviate some it the pain and discomfort.

Flashing is the telltale sign of parasitic infections that can cause scale and gill irritation, itching, shedding off scales, fin rot, pain, and even mortality if not treated on time.

Research has proven that the koi herpes virus can spread to wild common carp in the nearby waterways, which makes it essential for you to ensure that the infected koi is quarantined and treated immediately.

Note that a koi flashing because of a parasitic infection isn’t only dangerous for the sick fish but for the other aquatic creatures in the pond as well.

Shipping Stress

A koi is likely to be shipped at some point in its life, which can be a stressful experience for the fish.

Even though the stress of shipping is easy for the koi to recover from, it will exhibit some symptoms of stress as soon as you place it in its new home (pond).

A common symptom of shipping stress is flashing.

Note that pretty much every fish will dart when you release koi fish into a new pond.

The good news is that flashing due to a change in the habitat is only temporary. Koi is a hardy and strong fish and recovers quickly from shipping stress.

At times a koi fish takes only two to three minutes for the symptoms of flashing to subside after release.

Poor Water Quality

Is more than one koi in the pond exhibiting symptoms of flashing? If yes, it is most likely a water quality problem.

Poor water quality includes the presence of ammonia and nitrates, less oxygen, high or low KH and pH values, too much organic matter in the pond water, and high salinity.

This kind of situation creates an unstable and unhygienic environment that can result in stressing the koi fish and causing illness or disease.

The solubility of oxygen decreases as the temperature increases. This makes it difficult for the koi fish to survive in temperatures between 59 and 77 Degrees Fahrenheit.

Furthermore, anoxic and warm water creates prime habitat for the parasites and bacteria to thrive in. Therefore, make sure that the water-oxygen ratio doesn’t fall below 7 ppm.

Heavy Rainfall

Heavy rainfall can also alter the pH of the koi fish pond. In simpler words, water falling into the pond in such a large amount can change the koi fish pond’s temperature.

This can cause the koi fish to become stressed and ultimately reduces their resistance to illness, making them vulnerable to diseases.

As a result of the sudden change in pH, temperature fluctuation, and nutrient overload, the koi fish might start flashing due to discomfort and stress.

Clogged Gill Rakers

Gill rakers are situated on the gill arches of the koi fish. They function as a food filtering system for the koi.

Overeating can result in clogging the gill rakers, which can lead to flashing and jumping as the koi works to free its gills from excess food.

Koi flashing after food is one of the most common causes of changes in the koi’s behavior. However, it can also indicate that the food you are using isn’t suitable for the pond or the koi fish.

Overexposure to Sunlight

Like humans, koi fish, particularly the light-colored ones, are prone to sunburn. So, if your koi is exposed to too much sunlight, it can cause the fish’s pinkish skin turns darker, making the koi angrier.

The koi fish will start flashing in a desperate attempt to alleviate the pain, soothe their skin, and cool down. Sunburn can be extremely dangerous for koi fish.

However, unlike other reasons for flashings, sunburns are easy to spot as they literally look like burns and can be treated immediately. 

Poor Nutrition and Diet

Nutrient-deficient pellets are another reason why your koi fish might be flashing.

If your koi fish is lying on its side, floating on the surface of the pond, there’s a high chance that they are being served a poor diet.

Regardless of which specie you are breeding, every koi should be fed a varied diet that includes bloodworms, shelled peas, citrus fruits, wheat germ, spirulina, and well-balanced pellets.

Faulty Electrical Equipment

Electric equipment in ponds, such as pumps, fountains, and lights, can come in contact with water which can result in leaking voltage.

Even though the electric leak doesn’t cause the breaker to trip, it can irritate the koi fish swimming near the equipment, causing them to flash and jump. 

Changing the Pond’s Water without Decholrinating

The larger the koi pond water change, the higher the chances of your koi fish going into shock and flashing.

According to koi specialists, you should change 5 to 10 percent of the pond water every day. Frequently changing the pond water in small quantities helps the koi adapt and stay calm.

While changing the koi pond water, you also need to make sure that it is properly dechlorinated, as the presence of chlorine can cause chemical burns on the koi’s skin, which can result in flashing.

Chemical and Pesticides Runoff

Chemicals applied in your garden or lawn, like insecticides and pesticides, are likely to run off into the pond as soon as it starts raining.

Similarly, grass clippings and fertilizers can also end up in the pond, leading to nutrient overload and creating the ideal breeding ground for algae, fungi, and bacteria.

This can negatively affect the water quality and cause severe health issues for the koi, such as flashing and ich developing.

Is Koi Flashing a Serious Problem? When Should I Be Worried?

Flashing is a normal behavioral change as the koi starts to grow accustomed to the new environment. The stress of living with other fishes and the new environment can cause the koi to act out.

However, this type of flashing only lasts a couple of days. On the other hand, if your koi fish is flashing persistently, it can be a symptom of skin irritation, serious health issues, or poor water quality.

If one of two koi fish is flashing, and it isn’t consistent, then there is nothing to worry about. Flashing is a form of communication between the fish to attract males or to ward off predators.

How Do I Treat Koi Fish Flashing?

No matter what the cause of koi flashing, here are some tips to prevent it from happening again:

  • Make sure that your koi fish lives in a pond with good water quality.
  • Install a new filtration system.
  • Add plants and rocks to the pond.
  • Quarantine the infected fish as soon as you see it flashing.
  • Increase the pond’s oxygen levels.
  • Improve nutrition.
  • Reduce stress factors like bright lights, loud noises, and overcrowding.
  • Conduct regular health check-ups for the koi.
  • Frequently change the pond water in small quantities.

Final Thoughts

Now that we have gone through the main reasons that might cause your koi fish to flash. You should be able to distinguish between normal and serious flashing. 

Understanding the koi’s behavioral changes helps you know exactly when you need to react and how to find the root cause of the problem.

At the end of the day, koi fish are playful creatures and so flashing or jumping out of happiness is normal.

However, if your koi fish is flashing consistently, it could indicate an underlying problem.

So before all the koi fish in the pond start to flash, look for the aforementioned causes and treat the issue accordingly.

Other articles you may also like: