Good water is a vital ingredient of koi keeping and one that must never be compromised. Water quality is most likely to be variable in spring, when the ambient temperature is rising and daylight hours are increasing.
As the temperature rises, so does the bacterial count in the water. The parasitic population within the pond also increases as the water temperature rises above 10 degree Celsius. However, the koi, coming out of what may have been a long and stressful winter, are by implication weak.
Their immune system may have been almost completely shut down for six months or more and this, coupled with a lack of food, makes koi much more susceptible to bacterial and parasitic attack in spring.
At this time it is important to offer koi the correct diet in the right quantities. An unsuitable food supply can cause internal problems. Once the immune system is functioning at or near normal in summer, koi are able to cope with these problems without too much difficulty, but in spring, it is up to you to take steps to minimize any potential risks.
Once a systemic infection becomes established, causing severe swelling of the abdomen, swimming becomes difficult and a treasured life is lost. A solitary fish is always of concern for the koi keeper. If an established fish suddenly takes up this sort of behavior, or a new fish does this from day one, then you need to investigate the cause at once.
What is anchor worm or Lernaea? This is a small crustacean known as a copepod. With her head as an anchor embedded in the skin of the host fish, the female lays her eggs.
Lernaea looks like light colored sticks protruding from scales. To prevent anchor worm from multiplying, target the newly hatched, free swimming young with an appropriate water treatment.