The visionary of Phish has a very specific user interface in mind. He sketches out some pictures for us to get us started thinking about what this product will look like:
The quality of the user interface specification will range from the very crude (as you see here) to a polished and detailed specification provided by graphic artists. Even the most crude UI visualizaiton, however, can provide useful information at this stage of the analysis.
We can see that we need to keep track of elapsed time, the maximum and minimum numbers of each species of fish in the entire game etc. This diagram doesn't act as a specification, so much as a starting point for discussion. A more complete visualization will provide details on where the information is displayed, in what size font, how large the playing board is and so forth.