Rui CarmoFish is an aquarium simulator for Mac OS X that supports Rendezvous sharing of... fish. It also uses Growl for some notifications, and lets you tweak every little aspect of your virtual aquarium:
Fish is an aquarium simulator for Mac OS X that supports Rendezvous sharing of... fish. It also uses Growl for some notifications, and lets you tweak every little aspect of your virtual aquarium: