First there were robot dogs. Then robot cats. Now Japan's third-largest toymaker is betting that the craze for cyber-pets will take to the water.

At a Tokyo toy fair on Thursday, Takara Co. showed off a school of robot fish it says will swim into Japanese stores this fall.

In addition to finned fish, the Aquaroid Fish line includes a jellyfish and a crab. Fins, tentacles and pincers are all solar powered, and a computer brain keeps collisions with other marine life and aquarium walls to a minimum.

But these toys won't be an easy catch for younger shoppers: Takara said they will carry a price tag of 15,000 yen - about $140. The company hopes the line will appeal to mechanically-minded twenty- and thirtysomethings.

Sony Corp. started a ``virtual pet'' boom here when it introduced a robot dog called AIBO in May. Though priced at about $2,380 in Japan and $2,500 in the United States, all 5,000 AIBO dogs worldwide sold out in a matter of days. Sony then made 10,000 more and sold every one during a weeklong ``adoption program'' in November.

Information on whether the robot fish would be sold outside Japan was not available late Thursday.

[Updated 3/20//2000]