Because I'm feeling stressed.

The behavior of medaka swimming in circles in the tank is considered a sign of stress. They may feel stressed due to various factors such as poor tank conditions, changes in water quality, lack of proper hiding places, or overcrowding. It’s important to observe this behavior carefully and make environmental improvements and provide care to reduce the medaka’s stress.

Because the eyes are positioned high

The name “medaka” originates from the fact that their eyes are positioned high on the head. Inspired by this characteristic—eyes that are “high”—they were named “medaka.” Owing to their distinctive appearance, medaka are popular among enthusiasts and are also used for learning about and observing ecosystems.

Niigata Prefecture

The answer is Niigata Prefecture. In some areas of Niigata, there is a custom of eating medaka (Japanese rice fish). This region’s unique food culture may not be widely known in other prefectures. Because medaka are very small, they are seldom regarded as a common ingredient.

About 10 to 30 items

It is common for medaka (Japanese rice fish) to lay about 10 to 30 eggs in a single spawning. This number can vary somewhat depending on the fish’s environment and health, but it usually falls within this range. The medaka’s ability to produce so many eggs despite its small body highlights the wonders of nature and the mystery of life.

Siebold

The first person to introduce the Japanese rice fish (Nihon-medaka) to the world was Philipp Franz von Siebold. Siebold was a Dutch physician and naturalist active in Japan in the 19th century. He worked at the Dutch trading post in Nagasaki and collected a wide variety of natural specimens, including Japanese plants and animals, which he brought back to Europe and introduced there. Thanks to his achievements, Japan’s natural world became widely known in the West, and among it was the Japanese rice fish.

renal function

Among the bodily functions of medaka, the renal function is particularly well developed. Because the kidneys of medaka can efficiently expel excess water and waste products from the body, they are highly resilient to changes in water quality and possess strong survival capabilities. Thanks to this advanced kidney function, medaka can survive in a variety of environments.

saltwater bath

One way to revitalize medaka (Japanese rice fish) is a salt bath. A salt bath at an appropriate concentration is said to help reduce stress and prevent disease in medaka. This method is especially effective when external injuries or early symptoms of illness are observed. However, it is important to maintain the proper salinity, as excessive concentrations can adversely affect the fish, so caution is necessary. For details such as concentration and immersion time, it is best to consult specialized resources.