This is demo of a simple "avoid hitting the cave walls with your spaceship"-thing, except the spaceship is a fish. Apparently it was intended for a (budget?) release in the eighties, but that never happened. There's not a whole lot to say about this one. It was done by Richard Taylor, with music by Steve Barrett. Since the entry bar for making Commodore 64 games was quite low, there were a lot of abandoned projects like this, many of which are featured on C64 Games that Weren't. Here's their section on Richard Taylor: https://www.gamesthatwerent.com/gtw64/results/gy/0/gh/0/gc/0/gco/Richard+Taylor/ga/0/gs/0/go/0/