[Translated from French, so might not be completely accurate...]
Calypso is at the same time a game of memory and deduction. In the center of the table, 6 tiles show fish of different colors, with another colored fish on the reverse. There are 4 colors in total. When the die roll shows a blue fish, you must turn over a plate to reveal a blue fish. It is thus useful to remember the movements of the fish. But when your memory fails, your powers of deduction can take over.
Imagine that you must turn over a red fish and that the situation on the table is as follows:
Purple fish, Yellow fish, Yellow fish, Blue fish, Blue fish, Blue fish
You can deduce that a red fish is under purple fish. Indeed, the three blue fish are blue/red, blue/yellow and blue/purple. The two yellow fish are thus yellow/red and yellow/purple. The last fish is thus purple/red, the only missing combination.
This combination of reasoning and memory allows kids and adults to play each other. Whilst the adults can play the reasoning game, kids are generally much better at memory games!