I tried clicker conditioning a goldfish today. It seemed remarkably easy. There are 3 goldfish in the tank but one is very efficient at mopping up food so he's responded very well to clicker conditioning and I can basically ignore the other fish until they get jealous. Within about 15 minutes he was responding to a click by swimming to where the current would carry the food when I released it... smart fish. Another day of this and I'll probably give him an object to interact with... There are lots of videos on youtube of goldfish doing tricks. Does anyone else on here have a goldfish and if so would you like to try an informal challenge to teach it a trick or two? The clicker does not need to be under water.