Tokyo Sea Life Park has begun exhibiting fry of the unique ocellated icefish, after successfully hatching eggs from a pair of the rare creatures for the first time in the world earlier this month.
Put on display Thursday at the aquarium in Edogawa Ward are three larvae of the Antarctic Ocean-dwelling fish, the only vertebrate whose blood is transparent. The larvae are 2.2 to 2.5 cm in length, according to sea life spokesman Satoshi Tada.
On Tuesday, the aquarium announced it had managed to hatch the occellated icefish eggs May 7. As of Monday, about 20 larval fish had emerged from several hundred eggs, according to the facility, which in 2011 also became the first in the world to exhibit the unusual creatures.
Tada explained that a pair of ocellated icefish were brought to the aquarium in August 2011 after being caught in Antarctic waters by a fishing boat operated by Nippon Suisan Kaisha Ltd.
The ocellated icefish's blood is transparent because the creature "doesn't have hemoglobins in its red blood cells," Tada said, adding the reasons for this remain a mystery.
He noted that water temperature is the most important factor in keeping the larval fish alive, saying: "We try to keep the water temperature of the tank at 1 to 2 degrees. We have lots of ice made from seawater ready to inject whenever the temperature rises."