My son has Robo Fish desired (yes yes, the television advertising works). Very nice set incl. Plastic bowl and clown fish (Nemo). The tub is certainly not last forever, but our son had fun with it and wanted to directly have a Fish companions.
It is good that you do not have to feed the Robo-fish - let's see how long do the batteries :-)
Oh, and when you lift the fish out of the water, he soon ceases to fidget - already sure the batteries.