Displayed in this tank is a Western mosquito fish.

As the name suggests, they eat mosquito larva. Japanese name means eradicating all mosquitos. They were introduced to Japan about 100 years ago from overseas to exterminate mosquitos. These types are from North America. Until about 1970, they were only spotted in certain areas, but they have spread and now they can be found in waters south of Fukushima. They can grow up to be 5 cm in length.

Similar to a Japanese rice fish, they are omnivorous but are said to be highly aggressive. Also, while MinamiMedaka lays eggs, they are ovoviviparous. They are also known for having high reproductive powers, giving birth up to 300 babies at once.

The Ministry of Environment classifies them as invasive species. Along with largemouth bass, they are listed in the “100 worst invasive species of the world” category. Western mosquito fish brought to the areas by humans are causing problems in many locations around the world.