Phish is loosely based on Wator, which was invented by A. K. Dewdney, in his Computer Recreations article in the December, 1984 issue of Scientific American and on John Conway's famous simulation game, Life. The original vision statement set the tone for the project but doesn't supply a lot of detail:
In Phish, the world starts out populated by a variety of fish of many different species. Each species has rules about reproduction, movement, food supply, life span and size. These rules can change through spontaneous mutations, producing new animals with different characteristics. This game has no 'point', but it is interesting and it makes pretty patterns. The game will be given away as a promotional device.
Phish will allow us to focus on a number of important issues, including the transition between different states in an object, interactions among objects and the separation of the user interface from the underlying Phish mechanism.