Tokyo Sea Life Park Tokyo has put the giant rock crab on display for the first time in its "Ogasawara (Tide Pool)" tank in the marine area. The giant rock crab is a crab that inhabits rocky areas south of Amami Oshima, and when fully grown, its carapace can reach a width of about 6 centimeters. It had not been exhibited before because it was unclear whether it could coexist with the blenny fish that are in the same tank.

The blenny lives in rocky areas where waves come in and splashes, and it moves by leaping on the rocks rather than swimming in the water, feeding on algae and small animals. Because their habitat and food sources overlap with those of the giant rock crab, there was a risk that the giant rock crab could injure the blenny in the limited space of an aquarium.

Previously, we conducted a cohabitation experiment between the Japanese giant rock crab and the Japanese blenny, and the results showed that in a tank of a certain size, the problems we had been worried about were less likely to occur between the two species.
However, it was discovered that the giant rock crabs would steal the finely chopped shrimp and polychaete worms that were being given as food to the blenny. So, when shelled sweet shrimp were given to the giant rock crabs first, it was confirmed that the giant rock crabs would slowly eat only that food over the course of a day. This way, the blenny could also get some food.

We determined that cohabitation was possible if we could ensure that the giant rock crabs were fed reliably in a tank with sufficient space, and in late March 2014, we put two giant rock crabs on display in the exhibit tank.

However, perhaps due to the change in environment and the increase in hiding places, they immediately hide behind rocks when we approach to offer them food. Therefore, we are currently training the giant rock crabs to accept food by slowly approaching them without startling them.

They may be hiding in the shadows of rocks, but try looking for the giant rock crabs in the tank. If you see one holding something, it might be food given to it by animal keeper. You'll be able to watch it eat, holding onto the food tightly and tearing off small pieces with its claws.

Photo above: A giant rock crab holding a sweet shrimp.
Photo below: A blenny living together

[Tokyo Sea Life Park]

(April 11, 2014)