Q : Could you explain what Columnaris disease is?

A : This disease is an infection caused by the bacterium Flavobacterium columnare. It occurs at water temperatures above 18°C, and symptoms appear on the gills, fins, skin, and mouth. Symptoms include fins that become torn or eroded. There is excessive mucus secretion in the gills, and parts of the gills may be missing. Redness may appear around the mouth, and tissue loss may occur in severe cases.
Redness first appears around the affected area when the disease affects the body’s surface. Gradually, the mucus membrane peels away, causing uneven discolouration of the body. Since the symptoms appear different depending on the affected area, when the gills are affected, it is referred to as “gill rot”or “gill disease.” If the mouth is affected, it is called “mouth rot,” and if the fins are affected, it is known as “fin rot” or “tail rot.” As the condition progresses in all cases, there is a decrease in feeding behaviour, and swimming becomes sluggish.
Especially when symptoms are observed in the gills, the risk of death becomes high, so prompt treatment is essential. As a measure, administering medications that contain antibiotics is effective. The bacterium Flavobacterium columnare prefers low salinity environments, so using a 0.5% salt water bath in conjunction with antibiotic treatment is considered effective.

Q : When giving mash to Kego (a very early stage right after hatching), there is often a lot of leftover mash. Can this leftover mash be used as food for water fleas? Also, can rice bran be used for Kego and water fleas?

A : Water fleas feed on phytoplankton and rotifers. Phytoplankton are microorganisms that can cause green water. Therefore, mash and rice bran are unsuitable foods for water fleas. However, by scattering these substances, it is possible to stimulate the growth of phytoplankton and rotifers, which are foods for water fleas, thereby promoting their increase. Chicken manure is often used to grow water fleas. However, the manure itself isn’t food for them; instead, it helps increase the availability of their food sources. This operates on the same principle as described earlier. Kego eat rice bran, but because it is deficient in several essential nutrients, using organisms like water fleas as feed would result in higher yield rates. Nutritionally, mash may be superior to rice bran, but such organisms are often the better choice as feed.

Q : Do Koi sleep at night? Since the water temperature during the day in the summer is too high, I would like to feed them during the cooler hours. However, if they sleep at night, would it be a bad idea to feed them then? The water is from the tap, so the temperature doesn’t drop much, even if I add more water.

A : As I mentioned before regarding fish sleep, they don’t lie down to sleep like humans do. For fish, sleep behaviour can vary by species, but they generally sleep by swimming slowly or hiding in sheltered spots. Additionally, since they lack eyelids, their eyes stay open while they sleep. Koi are active during the day, becoming slower and less active at night. Like humans, fish can digest food while sleeping, so that’s not a problem. However, the water temperature might decrease at night. A fish’s digestive system is greatly influenced by water temperature. For Koi, they become more active at higher temperatures and less active at lower temperatures.
Water temperature significantly affects a fish’s digestive system. It becomes more active at higher temperatures and less active at lower temperatures. A common problem is feeding a lot of food in the evening when the water temperature is still high (since higher temperatures increase their activity and appetite). If the temperature then drops sharply at night, the fish may not be able to digest the large amount of food and can become unwell. Particularly in spring and autumn, where temperature fluctuations between day and night can be severe, it is vital to be cautious. However, since the water temperature does not drop in your case, this should not be a concern.